Computational Characterization of 

2-Azidocycloalkanamines: Notional Variations on the 

Hypergol 2-Azido-N,N-Dimethylethanamine (DMAZ) 

by Michael J. McQuaid 

ARL-TR-2806 September 2002 

Approved for public release; distribution is unlimited. 
NOTICES 

Disclaimers 

The findings in this report are not to be construed as an official Department of the Army position 

unless so designated by other authorized documents. 

Citation of manufacturer’s or trade names does not constitute an official endorsement or approval 

of the use thereof. 

Destroy this report when it is no longer needed. Do not return it to the originator. 
Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5066 

ARL-TR-2806 September 2002 

Computational Characterization of 

2-Azidocycloalkanamines: Notional Variations on the 

Hypergol 2-Azido-N,N-Dimethylethanamine (DMAZ) 

Michael J. McQuaid 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited.
ii

Abstract 

The fuel 2-azido-N,N-dimethylethanamine (DMAZ) has shown considerable promise as a 

replacement for hydrazine-based fuels in hypergolic propulsion systems, but the ignition delays 

observed for DMAZ-inhibited red fuming nitric acid (IRFNA) systems are longer than those for 

monomethylhydrazine-IRFNA systems. This report considers the potential of 

2-azidodocycloalkanamine-based fuels for addressing this issue. Such molecules have two 

stereochemically distinct isomers, one of which prevents the azide group from “shielding” the 

amine lone pair electrons from proton attack. The other promotes such shielding. Since 

shielding likely influences the manner in which nitric acid reacts with amine-azide fuels, the 

ignition delays for the isomers may be different, and it is possible that one of the isomers will 

yield shorter ignition delays than DMAZ. To support consideration of the synthesis and 

development of 2-azido-N,N-dimethylcyclopropanamine (ADMCPA) equilibrium structures are 

identified and their gas-phase heats of formations estimated via density functional theory-based 

calculations. In addition, ADMCPA isomer condensed-phase densities and heats of vaporization 

are estimated via molecular dynamics simulations performed with halogen analogs. Combined 

and employed to predict ballistic properties, the computational results indicate that the 

ADMCPA isomers merit further investigation as hypergols. A suggestion for synthesizing 

cis-ADMCPA is also proffered. 
iii

Acknowledgments 

Mr. D. Thompson (U.S. Army Aviation and Missile Command [AMCOM]) proposed proton 

attack of 2-azido-N,N-dimethylethanamine’s (DMAZ’s) amine lone pair electrons as an 

important step in the ignition of a DMAZ-inhibited red fuming nitric acid (IRFNA) system, 

raising steric shielding as an issue to be examined. The general idea of introducing a cyclic or 

bridging structure into DMAZ to prevent shielding was suggested by Dr. C. Chabalowski (U.S. 

Army Research Laboratory [ARL]) during one of our many discussions over the theoretical 

results obtained for DMAZ. Dr. N. Reynolds (Accelrys, Inc.) wrote the “script” employed to run 

the molecular dynamics simulations. Dr. S. Bunte (ARL) offered many helpful suggestions with 

respect to running the Accelrys polymer software codes. Dr. A. Kotlar (ARL) performed the ISP

calculations presented. The vast majority of the calculations reported were performed at the 

Department of Defense Major Shared Resource Center at Aberdeen Proving Ground. 
iv

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v

Contents 

Acknowledgments iii

List of Figures vii

List of Tables ix

1. Introduction 1

2. Computational Quantum Chemistry Methods 3

3. Computational Quantum Chemistry Results 4

3.1 ADMCPA........................................................................................................................4 

3.2 AMCBA and ACPA......................................................................................................11 

3.3 Gas-Phase Heats of Formation......................................................................................13 

4. Molecular Mechanics Methods and Results 14

5. Ballistic Properties 17

6. Synthesis Possibilities 17

7. Discussion 17

8. Summary 20

9. References 21

Appendix. Details From 2-Azido-N-methylcyclobutanamine (AMCBA) and 

2-Azidocyclopentanamine (ACPA) Theoretical Characterizations 25

Report Documentation Page 31 
vi

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vii

List of Figures 

Figure 1. The lowest energy DMAZ structure and a mapping of the electrostatic potential 

on its 0.004 atomic unit (a.u.) electron isodensity surface. Dark blue regions of the 

potential correspond to nucleophilic (lone pair electron) sites. .................................................2 

Figure 2. Equilibrium trans-ADMCPA conformers.......................................................................5 

Figure 3. Equilibrium cis-ADMCPA conformers. (H8 of conformers c-B and c-C is 

hidden in the perspectives shown.) ............................................................................................6

Figure 4. Simulated mid-IR absorption spectra for low energy trans-ADMCPA and 

cis-ADMCPA structures. .........................................................................................................11 

Figure 5. Equilibrium AMCBA conformers. (Arrows point to atoms hidden in the 

perspective shown.)..................................................................................................................12 

Figure 6. An equilibrium ACPA conformer. (Arrow points to atom hidden in the 

perspective shown.)..................................................................................................................13 

Figure 7. An equilibrium 3-azido-2-dimethylaminoaziridine conformer.....................................20 
viii

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ix

List of Tables 

Table 1. Geometric parameters for equilibrium ADMCPA conformers as computed via 

B3LYP/6-311++G(d, p).............................................................................................................7 

Table 2. Relative zero-point corrected energies, dipole moments, and rotational constants 

of equilibrium ADMCPA conformers as computed via B3LYP/6-311++G(d,p). ....................8 

Table 3. Harmonic vibrational frequencies and integrated IR intensities for transADMCPA conformers. ..............................................................................................................9 

Table 4. Harmonic vibrational frequencies and integrated IR intensities for cisADMCPA conformers. ............................................................................................................10 

Table 5. Gas-phase ∆Hf(298) estimates........................................................................................14 

Table 6. Condensed-phase property estimates..............................................................................16 

Table 7. NASA-Lewis thermochemical code ISP and D*ISP predictions for various fuels.a........18 

Table A-1. Geometric parameters for equilibrium AMCBA conformers as computed via 

B3LYP/6-311++G(d,p)............................................................................................................26 

Table A-2. Relative zero-point corrected energies, dipole moments, and rotational 

constants for equilibrium AMCBA conformers as computed via 

B3LYP/6-311++G(d,p)............................................................................................................27 

Table A-3. Harmonic vibrational frequencies and integrated IR intensities for 

equilibrium AMCBA conformers............................................................................................28 

Table A-4. Geometric parameters for an equilibrium ACPA conformer as computed via 

B3LYP/6-311++G(d,p)............................................................................................................29 

Table A-5. Harmonic vibrational frequencies and integrated IR intensities for an ACPA 

conformer as computed via B3LYP/6-311++G(d,p). ..............................................................30 
x

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1

1. Introduction 

Providing an extremely reliable basis on which to design intermittent and/or variable thrust 

propulsion systems, hypergolic liquid (or gel) fuel-oxidizer combinations—i.e., those that react 

spontaneously upon mixing—are employed throughout the Department of Defense (DOD) and 

National Aeronautics and Space Administration (NASA) for aviation and missile applications. 

One of the drawbacks to many “standard” hypergolic fuel-oxidizer combinations, however, is 

that the fuels are derived from hydrazine, monomethylhydrazine (MMH), and/or unsymmetrical 

dimethylhydrazine (UDMH)—all of which are acutely toxic and suspected carcinogens [1]. 

Searching for alternatives to hydrazine-based fuels, the Army (via the U.S. Army Aviation and 

Missile Command [AMCOM] and in collaboration with other DOD and NASA organizations) is 

investigating the use of various 2-azidoethanamines in such applications. Collectively referred 

to as Competitive Impulse Non-Carcinogenic Hypergols (CINCH) [2], the formulation within 

this class of compounds receiving the most attention is 2-azido-N,N-dimethylethanamine 

((CH3)2NCH2CH2N3). Also referred to as DMAZ, this fuel has been found to yield performance 

competitive with Aerozine 50 (a 50/50 mixture of hydrazine and UDMH) in inhibited red fuming 

nitric acid (IRFNA) oxidized experimental systems. DMAZ-IRFNA systems do not, however, 

meet “ignition delay” standards set by MMH-IRFNA systems, and this shortcoming may 

negatively impact the Army’s ability to field this alternative. 

Based on traditional chemical knowledge and testing performed for AMCOM, it was concluded 

that a rate-limiting step in DMAZ-IRFNA ignition might be associated with an initial chemical 

reactionnamely, proton transfer from nitric acid to DMAZ’s amine nitrogen [3]. As a result, 

one of the approaches to addressing the ignition delay issue has been to synthesize differently 

substituted 2-azidoethanamines with the hope of enhancing the amine’s reactivity/basicity. Two 

compounds synthesized subsequent to the identification of DMAZ as a promising hypergol are 

2-azido-N-methylethanamine (MMAZ) and 2-azido-N-cyclopropylethanamine (CPAZ), and a 

comparison of their attributes is instructive. MMAZ, which has a hydrogen atom in lieu of one 

of the methyl groups in DMAZ, is not hypergolic, while CPAZ, which has a cyclopropyl group 

in lieu of the methyl group in MMAZ, is. However, the hypothesis that the ignition delays for 

these fuels are, in fact, due to differences in the basicity of their amine nitrogen remains to be 

proven. 

In support of the experimentally based research being pursued through AMCOM, the U.S. Army 

Research Laboratory (ARL) is employing computational quantum chemistry in an attempt to 

identify the differences between fuels that correlate with ignition delay, the initial focus of this 

effort being the characterization of fuel-nitric acid proton transfer reactions. Toward 

characterizing DMAZ-nitric acid reactions, a study to establish the nature of DMAZ equilibrium 

structures was conducted [4], with 12 conformers being identified via density functional theory 
2

(DFT). One of the interesting findings of that study was that in DMAZ’s lowest energy structure 

(Figure 1), the azido group will shield the amine lone pair electrons from proton attack. Given 

the importance of proton transfer reactions inferred from experiments, this finding raised the 

possibility of molecular geometry having an influence in the ignition process. 

Figure 1. The lowest energy DMAZ structure and a mapping of the 

electrostatic potential on its 0.004 atomic unit (a.u.) electron 

isodensity surface. Dark blue regions of the potential 

correspond to nucleophilic (lone pair electron) sites. 

While considering means to explore this possibility, doubts about the value of a computational 

study arose, the concern being that even if a deleterious relationship between shielding and 

ignition delay could be established, an inability to prevent shielding would make the knowledge 

moot. This prompted the author to consider alternatives to 2-azidoethanamines. Informed that 

the introduction of a cyclic structure can “lock in” a preferred orientation between functional 

groups, the author sketched out a number of notional molecules based on the approach. Of the 

molecules sketched, 2-azidocycloalkanamines, the trans form of which prevents the azide group 

from coming in close proximity to the amine lone pair, were intuitively appealing. 

Stoichiometrically, 2-azido-N,N-dimethylcyclopropanamine (ADMCPA), 2-azido-Nmethylcyclobutanamine (AMCBA), and 2-azidocyclopentanamine (ACPA) differ from DMAZ 

by only one carbon atom, (C5H10N4 vs. C4H10N4), and, like DMAZ, the amine and azide groups 

are separated by two carbon atoms. Moreover, like CPAZ, which also has C5H10N4

stoichiometry, the cycloalkyl group should increase the reactivity of the amine lone pair. 

Therefore, if shielding of these electrons by the azido group is indeed a rate-determining 

mechanism in the ignition process, the cis and trans forms of a given azidocycloalkanamine will 

have different ignition delays, and it is possible that one of the forms will yield shorter ignition 

delays than DMAZ or CPAZ. AMCBA and ACPA will presumably be less reactive than 

ADMCPA, but might be worth synthesizing if ADMCPA proves to react too violently—a 

problem encountered in CINCH molecules synthesized with more than one azide functional 

group [2, 3]. 
3

It is, of course, a nontrivial exercise to experimentally synthesize and characterize a new 

compound, and the intuition of a computational chemist is hardly adequate justification for 

undertaking such a project. Therefore, computationally based property predictions were 

obtained to support consideration of 2-azidocycloalkanamine synthesis. Included are DFT-based 

characterizations of trans and cis ADMCPA equilibrium structures and their gas-phase heat of 

formation. A limited set of equilibrium AMCBA and ACPA conformers is also characterized. 

In addition, an approach to estimating the condensed-phase densities and heats of vaporization 

for azide-functionalized compounds based on molecular dynamics (MD) simulations with 

halogen analogs is proposed and validated, then employed to predict condensed-phase properties 

for the ADMCPA isomers. The property predictions are subsequently employed in ballistic 

performance calculations that provide a comparison of ADMCPA isomer specific impulses (ISP) 

and density specific impulses (D*ISP) relative to those for the CINCH fuels and MMH. Finally, 

a suggestion for synthesizing cis-ADMCPA is proffered. 

2. Computational Quantum Chemistry Methods 

The Gaussian98 (G98) suite of quantum chemistry codes [5] was employed to identify 

equilibrium ADMCPA, AMCBA, and ACPA structures and characterize their normal modes. 

The level of theory employed—DFT utilizing the B3LYP exchange-correlation functionals [6–8] 

and 6-311++G(d,p) atomic orbital basis set [9–11] on a G98-defined “ultrafine” grid—was 

chosen based on the success achieved with it in characterizing DMAZ [4]. In addition to the 

structural characterizations, estimates of gas-phase heats of formation at 298 K (∆Hf (298)) were 

sought for use in predicting ballistic performance. Unfortunately, the well-established approach 

for obtaining ∆Hf(298) estimates via the G2 method [12] proved computationally intractable, 

necessitating the implementation of an alternate method. The results presented in this report are 

derived from the heats of reaction (∆Hr(0)) calculated for “isodesmic” reactions at 0 K. 

(Isodesmic reactions are those in which the total number of each type of bond are equal in 

reactants and products; the success of the method assumed to be associated with the cancellation 

of errors achieved through equating product and reactant bonds [13].) In an attempt to identify if 

the method generated systematic errors, a variety of reactions involving the formation of 

molecules of interest and xH2 (x = 1 or 2) from reactants with accepted ∆Hf(298) values were 

constructed and their ∆Hf(298) predictions compared. The zero-point corrected energies and 

enthalpy differences at 298 and 0 K (H(298)-H(0)) for the reactants and reference elements 

needed to derive ∆Hf(298) from ∆Hr(0) were completed at the same level of theory as that 

employed to characterize the aliphatic amine azides of interest. The author also notes that 

though “accepted” H(298)-H(0) values are reported in the Joint Army-Navy-NASA-Air Force 

(JANNAF) thermochemical tables [14] for the reference elements (N2, H2, and C(=solid)) and a 

small subset of the reactants (NH3 and CH4), for internal consistency, the H(298)-H(0) values 
4

determined via the quantum chemical calculations are employed in all cases except C(solid). 

(H(298)-H(0) values for C(solid) are not calculable via the theoretical methods employed.) 

3. Computational Quantum Chemistry Results 

3.1 ADMCPA 

Figures 2 and 3 show, respectively, the equilibrium trans-ADMCPA and cis-ADMCPA 

structures identified through this study. The geometric parameters for these conformers are 

provided in Table 1, and Table 2 presents their zero-point corrected energies, dipole moments, 

and rotational constants. Beyond their classification as trans and cis forms, the conformers are 

distinguished by the (dihedral angle) orientations of the (CH3)2N- and -N3 groups about 

(CH3)2N-(C3H4) and (C3H4)-N3 bonds, and the labeling scheme was chosen such that 

alphabetically adjacent conformers are nominally transformed into one another by a dihedral 

angle rotation about one of these bonds. The scheme also groups conformers based on their 

H10-C9-N11-C12 angle’s proximity to one of three values. For trans-ADMCPA, these angles 

are !67° (t-A and t-B), 61° (t-C and t-D), and –165° (t-E and t-F). Conformers t-A and t-B are 

observed to be more than 4 kcal/mol lower in energy than the other conformers, indicating that 

the !67° H10-C9-N11-C12 angle is energetically favored. (In this configuration, the amine lone 

pair points toward and directly over the -(C3H4)- group.) Two different N2-N3-C4-C6 dihedral 

angles are also observed, 87° (t-A, t-D, and t-E) and !165° (t-B, t-C, and t-F), but for conformer 

pairs where this is the only primary difference—(t-A, t-B), (t-C, t-D), and (t-E, t-F)—the energy 

differences are small (≤0.2 kcal/mol). The six trans conformers identified are all of the 

structures that can be constructed from combinations of the geometric preferences observed. 

Based on a Boltzmann distribution calculated from trans conformer zero-point corrected 

energies, it is expected that t-A (58%) and t-B (41%) populations will dominate a gas-phase 

trans-ADMCPA sample at room temperature. 

The cis-ADMCPA conformers have energetically favored H10-C9-N11-C12 and N2-N3-C4-C6 

angles similar to those seen in the trans-ADMCPA conformers, but the correspondences between 

conformer energies and these angles are slightly different. Perhaps the most noteworthy 

difference is the 1.0 kcal/mol difference between conformers c-A and c-B. This difference is 

presumably related to the fact that c-A has a (stabilizing) azide-amine interaction similar to that 

observed in the lowest energy DMAZ conformer (Figure 1). In DMAZ, the conformer with this 

configuration is also lower in energy than otherwise similar conformers by 1.0–1.3 kcal/mol. 

Therefore, it is expected that c-A will prove to be the lowest energy cis-ADMCPA conformer. 

The six cis conformers identified are all of the structures that can be constructed from 

combinations of the geometric preferences observed. Based on a Boltzmann distribution 

calculated from cis conformer zero-point corrected energies, it is expected that c-A (82%) and 

c-B (18%) populations will dominate a gas-phase cis-ADMCPA sample at room temperature. 
5

Figure 2. Equilibrium trans-ADMCPA conformers. 
6

Figure 3. Equilibrium cis-ADMCPA conformers. (H8 of conformers c-B and c-C is hidden in the 

perspectives shown.) 
7

Table 1. Geometric parameters for equilibrium ADMCPA conformers as computed via B3LYP/6-311++G(d, p). 

trans conformers cis conformers 

Parametera t-A t-B t-C t-D t-E t-F c-A c-B c-C c-D c-E c-F 

Bond Length (in Angstroms) 

N1-N2 1.134 1.135 1.136 1.135 1.134 1.134 1.135 1.136 1.136 1.135 1.134 1.135 

N2-N3 1.232 1.232 1.231 1.233 1.233 1.233 1.228 1.230 1.230 1.231 1.234 1.231 

N3-C4 1.456 1.456 1.456 1.457 1.458 1.458 1.450 1.451 1.453 1.455 1.453 1.455 

H5-C4 1.086 1.086 1.086 1.086 1.085 1.085 1.082 1.087 1.087 1.087 1.087 1.087 

C6-C4 1.515 1.498 1.504 1.521 1.521 1.504 1.506 1.498 1.503 1.518 1.507 1.524 

H7-C6 1.083 1.083 1.082 1.083 1.084 1.083 1.084 1.083 1.083 1.082 1.083 1.083 

H8-C6 1.083 1.083 1.083 1.083 1.083 1.083 1.083 1.083 1.083 1.084 1.084 1.084 

C9-C6 1.510 1.510 1.503 1.504 1.526 1.528 1.513 1.509 1.502 1.504 1.519 1.500 

C9-C4 1.495 1.513 1.531 1.510 1.487 1.504 1.517 1.524 1.544 1.522 1.517 1.500 

H10-C9 1.095 1.095 1.086 1.087 1.086 1.085 1.096 1.097 1.088 1.088 1.084 1.085 

N11-C9 1.436 1.436 1.439 1.440 1.441 1.442 1.432 1.432 1.432 1.436 1.445 1.442 

C12-N11 1.460 1.461 1.459 1.459 1.455 1.456 1.460 1.460 1.458 1.459 1.459 1.460 

H13-C12 1.092 1.092 1.093 1.093 1.090 1.091 1.092 1.091 1.093 1.094 1.090 1.088 

H14-C12 1.093 1.093 1.093 1.093 1.092 1.092 1.093 1.093 1.093 1.093 1.092 1.093 

H15-C12 1.105 1.105 1.105 1.104 1.104 1.105 1.105 1.105 1.103 1.101 1.104 1.105 

C16-N11 1.460 1.460 1.455 1.455 1.460 1.460 1.461 1.460 1.456 1.456 1.460 1.461 

H17-C16 1.092 1.092 1.090 1.091 1.093 1.093 1.091 1.091 1.091 1.091 1.092 1.093 

H18-C16 1.093 1.093 1.092 1.092 1.093 1.093 1.093 1.092 1.093 1.093 1.092 1.092 

H19-C16 1.105 1.105 1.105 1.106 1.105 1.104 1.105 1.106 1.101 1.101 1.105 1.105 

Simple Angle (in Degrees) 

N1-N2-N3 172.9 172.9 173.2 173.1 173.0 172.9 172.2 172.7 173.1 173.0 172.3 173.1 

N2-N3-C4 116.0 116.1 116.3 115.9 115.8 116.0 118.8 116.6 116.4 116.1 115.9 115.7 

N3-C4-H5 115.1 115.4 100.6 102.5 102.8 101.9 109.1 114.4 114.6 114.4 114.0 113.3 

N3-C4-C6 119.9 116.3 116.6 120.1 120.2 116.7 123.6 116.0 115.4 118.5 116.4 120.1 

C4-C6-H7 116.7 117.1 117.0 116.6 116.2 116.5 117.2 114.9 114.8 115.7 115.4 115.4 

C4-C6-H8 117.8 116.9 117.1 118.0 118.3 117.5 118.3 119.0 119.1 118.8 118.7 119.0 

C4-C6-C9 59.3 60.4 61.2 59.9 58.4 59.5 60.3 60.9 61.8 60.5 60.2 58.9 

C4-C9-H10 114.7 115.4 113.1 112.5 112.9 113.4 115.6 113.9 111.8 112.3 112.9 111.8 

H10-C9-N11 117.2 117.2 111.5 111.5 111.3 111.2 116.8 116.2 111.3 111.3 111.2 109.8 

C9-N11-C12 112.2 112.2 111.6 111.4 116.8 116.8 112.8 112.3 112.9 112.6 116.5 117.0 

N11-C12-H13 109.8 109.8 109.7 109.7 99.7 110.6 109.9 109.9 109.6 109.5 110.6 110.5 

N11-C12-H14 109.5 109.5 109.6 109.5 146.6 108.6 109.5 109.4 109.5 109.4 108.6 108.5 

N11-C12-H15 112.8 112.8 113.1 113.1 102.5 113.9 112.7 112.9 113.8 113.3 112.8 112.8 

C9-N11-C16 112.0 112.2 117.3 117.1 110.9 110.9 111.9 112.2 118.9 119.2 111.9 111.1 

N11-C16-H17 109.8 109.9 110.5 110.5 109.7 109.7 109.6 110.2 110.1 110.1 110.1 110.1 

N11-C16-H18 109.5 109.6 108.6 108.6 109.5 109.5 109.5 109.5 108.3 108.1 109.2 109.1 

N11-C16-H19 112.8 112.8 114.0 114.0 27.6 113.0 112.6 112.7 114.1 114.3 113.2 113.1 

Dihedral Angle (in Degrees) 

N1-N2-N3-C4 174.8 !172.6 !172.0 173.1 175.9 !173.5 !172.0 171.7 173.9 !169.1 168.7 !172.2 

N2-N3-C4-H5 !60.9 50.6 50.9 !57.6 !59.1 55.8 157.0 !49.7 !47.6 51.7 !59.9 51.6 

N2-N3-C4-C6 87.5 !165.8 !167.0 89.4 86.6 !163.3 37.0 167.4 169.2 -96.1 157.0 !94.4 

N3-C4-C6-H7 !146.8 !141.2 !138.0 !143.8 !144.9 !139.6 !4.7 !5.6 !2.0 2.9 !2.9 !2.3 

N3-C4-C6-H8 !2.0 2.7 3.4 !1.5 !1.6 2.9 139.7 137.8 138.9 145.0 138.8 140.3 

N3-C4-C6-C9 105.3 110.7 110.4 105.0 105.0 110.2 !110.7 !112.5 !111.8 !106.3 !111.5 !109.7 

N3-C4-C9-H10 !4.5 1.0 !0.1 !5.5 !7.1 !2.0 !139.3 !149.0 !150.2 !144.8 !148.4 !143.7 

C6-H10-C9-N11 !144.9 !145.6 147.9 !146.1 !145.5 !146.1 !145.3 !146.8 147.8 !146.7 !143.4 !145.2 

H10-C9-N11-C12 !66.6 !67.4 60.8 61.7 169.0 169.0 !68.1 !69.5 65.4 68.9 !154.9 !168.7 

C9-N11-C12-H13 !55.6 !55.5 !51.1 !51.1 !58.6 !58.8 !55.6 !56.0 !47.1 !48.0 !54.2 !53.9 

C9-N11-C12-H14 !174.4 !174.2 !169.6 !169.6 !172.4 !176.3 !174.4 !174.7 !165.3 !166.0 !172.4 !172.2 

C9-N11-C12-H15 65.1 65.3 69.6 69.4 65.7 64.0 65.2 64.9 73.8 72.8 67.8 68.4 

H10-C9-N11-C16 60.3 59.6 !167.6 !167.2 !61.1 !61.3 59.4 57.4 !157.5 !154.1 !25.5 !40.1 

C9-N11-C16-H17 55.5 56.4 56.1 56.8 52.4 52.5 55.5 56.3 54.7 53.3 53.5 53.7 

C9-N11-C16-H18 174.3 175.0 173.7 174.4 170.8 170.9 174.2 175.0 171.8 170.2 171.6 171.9 

C9-N11-C16-H19 !65.2 !64.4 !66.6 !66.0 !68.1 !68.2 !65.4 !64.6 !67.7 !69.5 !68.1 !67.7 a

 Labels refer to Figures 1 and 2. 
8

Table 2. Relative zero-point corrected energies, dipole moments, and rotational constants of 

equilibrium ADMCPA conformers as computed via B3LYP/6-311++G(d,p). 

Conformer Designation ∆E 

(kcal/mol) 

μ 

(Debye) 

Rotational Constants 

(GHz) 

trans conformers

t-A —a 2.56 4.81 0.76 0.68 

t-B 0.2 2.53 3.21 0.93 0.76 

t-C 4.4 2.53 2.85 0.99 0.81 

t-D 4.4 2.40 4.07 0.79 0.73 

t-E 4.8 2.88 5.03 0.73 0.71 

t-F 5.0 2.98 3.31 0.85 0.79 

cis conformers 

c-A —b 2.95 2.32 1.31 1.15 

c-B 1.0 2.87 2.69 1.14 0.88 

c-C 4.3 1.94 2.28 1.28 1.02 

c-D 4.7 1.74 2.92 0.99 0.92 

c-E 5.4 2.87 2.50 1.14 0.96 

c-F 6.2 2.64 4.09 0.86 0.78 a

 Zero-point corrected energy is –415.401984 Hartrees. 

b

 Zero-point corrected energy is –415.399113 Hartrees. 

The relative energies of the lowest energy trans- and cis-ADMCPA conformers also deserve 

note. That is, despite c-A having the stabilizing amine-azide interaction found in DMAZ, it is 

still 1.8 kcal/mol higher in energy than the lowest energy trans-ADMCPA structure (where this 

interaction is precluded). The accuracy of the energy calculations is assumed to be from 1 to 

3 kcal/mol, so the true energy ordering is uncertain. But it may be found that the two isomers 

yield different (overall) reaction exothermicities in an otherwise similar system. 

With 19 atoms and Cs symmetry, all ADMCPA conformers have 51 normal modes. Frequency 

values and (integrated) infrared (IR) intensities for transitions to all modes of each conformer are 

provided in Tables 3 and 4. Lacking experimental mid-IR absorption spectra with which to 

compare, the results are considered to have limited value at this time, and so are not discussed in 

detail. However, they do indicate that if ADMCPA molecules are synthesized, the acquisition of 

mid-IR absorption spectra in the range from 400 to 900 cm–1 will reveal which structures are 

present in the sample. Simulating mid-IR absorption spectra (I(v)) by modeling vibrational band 

contours (due to rotational line structure) with a Lorentzian lineshape, 

( )2 2

/ ( )

ν ν γ

γ π

− + = ∑

j j

Aj I v , (1) 

where Aj is the integrated absorption for a transition to the j

th normal mode and γ (equal 10 cm–1) 

is the lineshape width at half-maximum, Figure 4 shows that the presence of cis-ADMCPA will 

be identifiable by the presence of a feature at about 590 cm–1, and that c-A and c-B will be 

identified/distinguished by the concomitant appearance of features near either 650 cm–1 or 700 

cm

–1. The presence of a feature at 447 cm–1, on the other hand, will identify the presence of 

trans-ADMCPA. 
9

Table 3. Harmonic vibrational frequencies and integrated IR intensities for trans-ADMCPA conformers. 

Mode Conformer 

t-A t-B t-C t-D t-E t-F 

ν A ν A ν A ν A ν A ν A 

1 33 0.0 34 0.2 35 0.0 31 0.0 33 0.1 30 0.1 

2 85 0.4 89 0.5 56 0.5 56 0.5 43 0.2 49 0.3 

3 136 1.1 107 0.4 103 1.3 121 0.6 124 0.3 108 0.0 

4 159 0.8 192 1.2 194 0.1 154 3.1 179 0.6 209 2.3 

5 225 1.2 222 1.2 227 0.9 230 1.4 234 0.7 225 0.2 

6 242 0.3 243 0.0 249 0.3 245 0.8 249 0.4 252 0.3 

7 278 4.7 270 1.2 266 2.4 279 0.6 268 1.5 258 1.4 

8 308 1.5 328 1.0 327 5.1 327 3.1 292 3.0 323 2.9 

9 389 3.6 389 10.6 391 12.8 391 8.0 379 9.8 381 11.2 

10 406 4.9 401 5.6 400 1.8 400 4.1 426 1.9 424 3.6 

11 447 2.1 446 1.7 459 2.1 460 1.3 464 1.8 458 1.6 

12 490 0.4 492 1.9 506 5.5 508 2.2 505 5.9 504 4.3 

13 554 9.1 549 8.4 544 5.8 555 8.9 556 8.4 552 7.4 

14 654 14.2 645 13.5 642 20.4 645 14.3 659 15.6 639 13.9 

15 774 8.5 785 6.3 762 8.2 756 14.8 740 4.9 753 10.5 

16 839 1.3 829 7.1 816 6.7 832 7.9 825 15.9 818 3.1 

17 929 36.4 929 25.1 863 34.5 903 15.6 901 12.9 892 35.3 

18 952 9.9 934 17.4 931 3.8 932 8.4 915 6.4 918 8.4 

19 969 6.5 977 9.4 961 12.1 942 5.5 966 19.4 975 10.4 

20 1031 18.0 1032 15.3 1027 13.5 1024 21.8 1012 19.6 1016 16.7 

21 1056 6.8 1055 9.8 1061 16.0 1059 14.5 1040 22.9 1057 22.2 

22 1062 16.7 1079 11.5 1081 5.8 1070 11.1 1061 15.3 1060 9.8 

23 1094 0.8 1094 10.2 1100 33.0 1087 11.9 1094 10.2 1103 5.4 

24 1106 10.2 1111 2.3 1113 7.5 1111 28.6 1109 24.1 1110 23.2 

25 1117 4.3 1116 4.2 1121 5.8 1114 6.8 1115 5.2 1119 10.1 

26 1145 1.4 1146 2.4 1147 4.7 1147 1.3 1151 5.9 1155 12.2 

27 1186 17.5 1184 16.0 1174 10.5 1175 8.8 1175 10.6 1175 9.0 

28 1223 4.5 1224 5.2 1219 15.3 1219 18.7 1215 20.8 1209 7.5 

29 1243 20.3 1241 20.8 1243 10.8 1243 13.8 1241 10.1 1238 10.6 

30 1311 6.9 1309 8.4 1319 13.3 1314 10.4 1309 34.8 1310 28.1 

31 1314 38.4 1314 12.1 1331 113.8 1325 195.5 1325 172.7 1326 129.0 

32 1331 210.2 1331 164.0 1350 40.6 1347 21.1 1354 39.3 1354 51.9 

33 1413 4.1 1406 28.3 1416 17.0 1420 4.0 1425 1.6 1419 13.2 

34 1441 0.0 1440 0.0 1442 0.6 1442 0.7 1441 0.4 1441 0.3 

35 1463 4.9 1465 6.1 1473 0.3 1472 0.8 1471 2.3 1472 2.5 

36 1483 7.4 1483 7.1 1484 5.4 1484 13.6 1484 10.6 1483 21.1 

37 1488 9.7 1485 21.4 1485 28.2 1486 10.4 1493 13.7 1488 19.4 

38 1498 6.2 1497 9.6 1500 5.1 1500 7.1 1499 11.6 1499 8.1 

39 1499 21.3 1498 20.4 1502 25.0 1502 22.6 1501 15.6 1501 15.6 

40 1515 10.4 1514 10.5 1517 16.6 1518 17.3 1517 15.2 1516 14.8 

41 2234 699.9 2232 626.8 2228 648.9 2229 686.9 2232 676.5 2232 645.5 

42 2922 49.3 2922 43.8 2914 64.4 2911 75.0 2916 62.8 2918 63.0 

43 2929 149.3 2929 145.1 2927 98.3 2931 97.8 2929 116.8 2931 120.4 

44 3024 48.2 3025 51.2 3056 31.8 3056 34.1 3056 33.6 3056 32.4 

45 3059 21.8 3058 22.2 3065 33.6 3065 33.8 3067 26.0 3067 25.3 

46 3061 39.9 3061 38.6 3098 25.2 3098 25.0 3098 22.5 3098 22.7 

47 3103 14.6 3101 21.2 3111 17.5 3109 20.0 3107 33.8 3107 31.7 

48 3105 37.9 3105 31.1 3124 3.3 3122 2.9 3127 5.6 3130 5.8 

49 3129 8.9 3132 8.1 3130 22.7 3128 27.2 3136 4.9 3135 4.2 

50 3134 8.5 3135 8.6 3136 11.7 3134 9.2 3141 16.2 3139 19.3 

51 3222 4.2 3225 3.5 3219 5.1 3218 5.6 3215 6.6 3218 5.6 

Notes: ν = cm!1; A = kilometers per mole.

 
10

Table 4. Harmonic vibrational frequencies and integrated IR intensities for cis-ADMCPA conformers. 

Mode Conformer 

c-A c-B c-C c-D c-E c-F 

ν A ν A ν A ν A ν A ν A 

1 50 0.1 32 0.0 40 0.1 27 0.1 26 0.1 28 0.3 

2 85 0.0 77 0.3 69 0.8 75 1.5 60 0.1 56 0.4 

3 135 2.2 149 1.1 151 3.9 102 0.9 158 1.5 114 0.5 

4 191 1.0 166 1.4 172 1.4 189 5.9 183 1.7 213 3.8 

5 227 1.9 227 0.2 214 1.1 213 0.8 240 1.1 233 2.7 

6 241 0.2 240 0.4 228 0.5 225 1.2 263 2.4 257 0.9 

7 257 0.4 259 0.7 282 7.7 280 2.5 288 1.1 265 1.5 

8 334 5.6 329 5.1 297 1.5 291 5.3 322 3.8 311 1.2 

9 386 1.3 373 5.0 384 7.6 382 2.2 378 2.2 372 1.5 

10 409 1.6 398 3.1 403 1.0 402 3.2 419 1.1 420 1.9 

11 496 2.8 494 1.1 501 1.5 500 3.2 498 4.9 500 4.2 

12 537 11.2 545 8.2 535 7.5 548 7.9 553 8.5 551 9.5 

13 592 3.8 589 5.4 588 21.9 605 0.7 574 9.2 592 1.7 

14 701 17.0 656 18.4 656 6.7 628 39.0 662 20.1 637 13.5 

15 750 5.0 753 5.8 712 2.7 718 2.9 737 7.5 724 9.3 

16 788 14.5 808 0.8 782 7.8 808 10.9 781 4.4 794 33.0 

17 838 12.6 839 14.3 827 6.7 831 7.4 829 3.7 840 1.3 

18 938 39.7 938 36.3 909 13.6 918 12.0 933 15.9 931 24.3 

19 976 1.7 987 6.0 965 26.2 990 21.1 955 18.2 964 6.0 

20 1042 9.1 1049 7.9 1054 2.8 1029 3.6 1038 5.1 1023 6.5 

21 1056 7.1 1058 7.1 1065 12.7 1060 5.0 1062 30.7 1039 18.1 

22 1066 20.5 1074 10.8 1074 4.4 1069 14.7 1073 7.4 1061 28.8 

23 1096 6.5 1102 4.3 1105 19.0 1103 9.3 1092 19.2 1093 9.8 

24 1117 4.0 1116 4.2 1116 3.3 1109 3.8 1115 3.3 1115 5.4 

25 1130 1.0 1129 0.5 1126 7.7 1115 4.1 1119 6.1 1125 1.4 

26 1137 2.5 1149 4.9 1154 1.7 1159 1.8 1147 12.8 1158 14.8 

27 1186 16.1 1183 14.4 1171 8.5 1173 5.7 1174 11.1 1177 12.6 

28 1201 2.1 1213 11.3 1212 8.1 1214 23.0 1214 11.7 1228 27.6 

29 1242 20.9 1242 21.5 1252 19.4 1251 19.6 1237 13.6 1234 12.4 

30 1314 6.1 1314 5.2 1329 33.6 1324 52.3 1316 41.0 1320 70.8 

31 1361 98.4 1337 44.3 1349 31.1 1350 34.8 1327 45.1 1338 28.8 

32 1389 38.8 1373 137.8 1370 108.3 1368 124.6 1366 111.3 1378 141.5 

33 1397 7.0 1397 24.7 1404 13.2 1406 10.7 1418 9.2 1425 2.7 

34 1441 0.5 1441 0.2 1443 0.7 1440 0.6 1442 1.2 1442 2.3 

35 1467 3.5 1467 9.0 1474 2.6 1472 3.2 1474 8.5 1471 6.6 

36 1482 8.4 1482 5.7 1483 10.2 1480 13.9 1485 6.9 1485 10.7 

37 1485 10.2 1484 16.9 1485 18.1 1483 9.9 1489 21.5 1490 19.5 

38 1497 6.1 1497 10.4 1497 8.0 1497 9.6 1500 7.0 1501 3.8 

39 1500 15.8 1498 11.3 1507 3.5 1509 1.9 1507 2.6 1505 8.7 

40 1514 10.2 1514 10.0 1523 17.9 1525 18.6 1518 17.1 1518 15.8 

41 2239 518.1 2229 628.6 2231 636.2 2233 731.5 2233 628.4 2234 753.1 

42 2922 45.2 2914 45.0 2940 65.4 2961 59.6 2920 63.6 2918 43.3 

43 2929 157.9 2922 159.0 2959 74.8 2967 77.8 2928 154.6 2926 156.4 

44 3008 73.3 2994 72.1 3050 36.9 3049 42.6 3058 29.0 3056 33.0 

45 3061 20.6 3059 27.5 3060 37.8 3057 38.3 3068 28.5 3068 34.7 

46 3064 30.8 3064 30.4 3091 24.3 3086 30.1 3099 27.4 3098 29.9 

47 3105 21.8 3105 20.0 3096 16.7 3096 14.5 3105 15.5 3106 12.2 

48 3113 18.1 3110 27.9 3102 22.6 3100 24.8 3121 10.8 3122 8.5 

49 3123 5.8 3117 18.4 3112 29.9 3112 33.1 3128 11.1 3141 3.4 

50 3183 9.2 3130 9.7 3133 14.1 3131 11.9 3148 15.2 3143 18.5 

51 3210 7.8 3220 5.8 3218 5.9 3218 5.8 3217 6.9 3213 7.7 

Notes: ν = cm!1; A = kilometers per mole.
11

Figure 4. Simulated mid-IR absorption spectra for low energy trans-ADMCPA 

and cis-ADMCPA structures. 

3.2 AMCBA and ACPA 

The equilibrium AMCBA and ACPA structures identified through this study are shown in 

Figures 5 and 6, respectively. The conformers in these limited sets were obtained via geometry 

optimizations started with structures expected (based on the ADMCPA characterizations) to be 

energetically favored. Shielding configurations in trans isomers were also sought. Complete 

geometric parameters and normal mode details for the structures in these figures are provided in 

the Appendix. Briefly, as in DMAZ and cis-ADMCPA, the cis isomers of AMCBA and ACPA 

have configurations with interacting amine and azide groups that are 1.0 kcal/mol lower in 

energy than otherwise similar conformers. Thus, a population dominated by a shielded 

configuration is expected for the cis forms. As for trans-AMCBA and trans-ACPA, the 

increasing flexibility of their rings allows closer proximity of the azide and amine groups than 

in trans-ADMCPA; the N2-N(amine) distance measuring their separation decreases from 

4.29 Å in trans-ADMCPA [t-B] to 3.71 Å in trans-AMCBA and 3.16 Å in trans-ACPA. The 

N2-N(amine) separation in trans-ACPA is very close to the 3.07-Å N2-N(amine) separation in 

the lowest energy DMAZ structure, limiting the author’s interest in further characterization of 

this molecule. 
12

 c-A c-B 

 t-A t-B 

N1

N2 

N3 

C4 H5

C6 

N1

C9 

C12 

C16 

C1

C12

C4

C9 

C6 

C4 

C6 

C12 C9 

C16 

C6

C4

C12

C9 

C16 

N3 

N2 

N1

N1

N2

N3

N1 N13 

H7

H1

H11 

H8

H1

H1

H1

H17 

H1

H17

H18 H19 

H1

H1

H5

H5

H7

H8

H5

N1

N2

N3

N14

H8 

H5

H15 

H18 

H11 H10 

H13 

H19 

H17 

H19

H18 

H17

H13

H8

H7

H10 

H11 

H15

H5

H7 

Figure 5. Equilibrium AMCBA conformers. (Arrows point to atoms hidden in the perspective shown.) 
13

N1 N2 

N3 

N17

C6 

C9 C4 

C12

C15

H5 

H8 H7 

H11 

H10 

H13 H14 

H16

H18

H19

Figure 6. An equilibrium ACPA conformer. (Arrow points to 

atom hidden in the perspective shown.) 

3.3 Gas-Phase Heats of Formation 

Table 5 shows the gas-phase ∆Hf(298) estimates obtained for various alkanes, aliphatic amines, 

CINCH compounds, and the ADMCPA isomers based on calculated ∆Hr(0) values for isodesmic 

reactions. However, one of the concerns with such estimates, i.e., an inability to identify and 

correct systematic error [13], raises a question about their reliability and requires comment. The 

author attempted to address this issue by constructing isodesmic reactions in a consistent manner, 

i.e., forming the molecule of interest and H2 from reactants with accepted ∆Hf(298) values. For 

alkanes and aliphatic amines with accepted ∆Hf(298) values, this method yields reasonably 

accurate, but systematically high (0–3.5 kcal/mol), estimates. This suggests that the method’s 

values can, in fact, be rationalized and was the basis for extending the method to obtain ∆Hf(298)

estimates for the azide-functionalized molecules in the table. 

Another general concern in predicting ∆Hf(298) via theoretical results for isodesmic reaction 

schemes—namely, the necessity of good experimental heat of formation values for all (assumed) 

knowns—proves to be an issue for the azide-functionalized fuels and also requires comment. 

First, the bonds in the azido group are unique in nature—i.e., they are not reliably represented as 

single, double, or triple bonds, or by other “common” bonds—and thus the isodesmic schemes 

must include an azido compound as a reactant. Unfortunately, the only simple azide compound 

with a reliable heat of formation value is hydrozoic acid (HN3). Heats of formation for methyl 

azide and ethyl azide would have been valuable, but published experimental values could not be 

found, and there are indications that values obtained with the G2 method are from 2 to 

3 kcal/mol too low [15]. Thus the ability to compare values from different isodesmic schemes 

and identify systematic errors is limited. Based on the author’s “best estimates” for the 

∆Hf(298)’s of methylazide and ethylazide and an experimentally obtained ∆Hf(298) for 
14

Table 5. Gas-phase ∆Hf(298) estimates. 

Compound ZPE H(298)-H(0) ∆Hf(0) ∆Hf(298) Diff. Isodesmic Reaction Scheme 

 

(a.u.) 

JANNAF 

(kcal/mol) 

Calc 

(kcal/mol)

Expa 

(kcal/mol)

Calc 

(kcal/mol)

Expb 

(kcal/mol)

Calc 

(kcal/mol)

 

C(solid) 0.25 0.0 0.00 

H2 !1.169506 2.02 2.07 0.0 0.00 

N2 !109.554124 2.07 2.07 0.0 0.00 

Ammonia !56.548462 2.40 2.40 !9.3 !10.97 

Methane !40.489427 2.40 2.39 !16.0 !17.90 

Cyclopropane !117.850067 2.71 17.0 12.75 

Hydrazoic acid !164.814684 2.62 71.8 70.30 

Ethane !79.782286 2.78 !16.3 !15.0 !20.23 !18.9 1.3 CH4+CH4→Ethane+H2

Butane !158.374256 4.23 !23.0 !19.5 !30.14 !26.7 3.5 2 Ethane→Butane+H2

Methylamine !95.830097 2.75 !1.8 !1.3 !5.49 !5.0 0.5 CH4+NH3→MeNH2+H2

Ethylamine !135.129229 3.37 !5.6 !4.7 !11.00 !10.1 0.9 CH4+MeNH2→EtNH2+H2

 !5.5 !10.9 0.1 Ethane+NH3→EtNH2+H2

Cyclopropylamine !173.202101 3.39 24.1 24.6 18.42 19.0 0.5 (CH2) 3+NH3→CpNH2+H2

Dimethylamine !135.117679 3.37 0.9 2.5 !4.50 !2.9 1.6 CH4+MeNH2→Me2NH+H2

Diethylamine !213.715623 4.95 !8.8 !5.3 !17.30 !13.8 3.5 Ethane+EtNH2→Et2NH+H2

Trimethylamine !174.408125 4.02 1.4 3.4 !5.70 !3.7 2.0 CH4+Me2NH→Me3N+H2

Methyl azide !204.103331 3.40 75.5 75.5 (73) 72.4 (!0.6) CH4+HN3→MeN3+H2

Ethyl azide !243.402659 4.07 71.1 71.1 (68) 66.4 (!1.6) Ethane+HN3→EtN3+H2

1-azidobutane !321.995173 5.28 64.0 59.9 55.9 !4.0 Butane+HN3→BuN3+H2

MMAZ !338.036614 5.56 86.5 78.8 CH4+EtNH2+HN3→MMAZ+2H2

DMAZ !377.325354 6.33 88.0 75.6 78.8 3.2 Me2NH+Ethane+HN3→DMAZ+2H2

CPAZ !415.40821 6.53 112.6 103.4 (CH2)3+EtNH2+HN3→CPAZ+2H2

trans-ADMCPA !415.401984 6.66 115.7 106.7 Me2NH+(CH2)3+HN3→ADMCPA+2H2

cis-ADMCPA !415.399113 6.56 117.5 108.4 Me2NH+(CH2)3+HN3→ADMCPA+2H2

a

 “Experimental” ∆Hf(0) values are the sum of experimental (exp) ∆Hf(298) values and calculated (calc) H(298)-H(0) values. b

 Values in parentheses are estimates proposed by the author based on consideration of results published by Rogers and McCafferty [15] and Lee et al. [16]. 

1-azidobutane [16], the aliphatic azide ∆Hf(298) values appear to be underpredicted. But since 

these underpredictions are coupled with (expected) slight overpredictions for the (isodesmic) 

formation of secondary and tertiary amines from primary and secondary amines, the author 

expects that the Table 5 ∆Hf(298) estimates for the aliphatic amine azides from these schemes 

will prove to be reasonably accurate. An experimental value for DMAZ has been established 

[2, 3] and indicates that the theoretically based prediction is approximately 3 kcal/mol (5%) too 

high. However, given the lack of corroborating evidence for the experimental value, this issue is 

considered an open one. 

4. Molecular Mechanics Methods and Results 

In addition to the gas-phase properties characterized, the author was interested in estimating 

condensed-phase densities and heats of vaporization for each ADMCPA isomer. Coupled with 

the gas-phase heats of formation determined, such property predictions can be employed in 
15

calculations to predict a fuel’s performance in a propulsion system. Having been employed 

successfully by Bunte and Sun for predicting/estimating the density of nitrate esters [17], an 

approach for obtaining condensed-phase properties based on the Molecular Simulations, Inc. 

(MSI, now Accelrys, Inc.) suite of molecular modeling codes and its COMPASS force field [18] 

was desired. However, COMPASS force field parameters for azide atom types had not been 

developed at the time of the study, so the use of “azide analogs” in the simulation routines had to 

be considered. The properties of notional azide compounds are commonly predicted based on 

their halogen analogs, and a specific approach for predicting densities was suggested by the work 

of Lee et al. [16], who found that the (experimentally determined) densities of ω-azidoalkanes 

are nearly identical to those of their monochloride analogs. In addition, these researchers found 

that the heats of vaporization of ω-azidoalkanes are close to those of their monobromide analogs. 

To establish that the correspondences observed by Lee et al. would be found computationally, 

MD simulations with the monochloride and monobromide analogs of DMAZ, CPAZ, MMAZ, 

and 1-azidobutane were set up and run. The simulations were performed on cubic threedimensional periodic cells containing 1080–1100 atoms (56–72 molecules) constructed by the 

Amorphous Cell module of Insight II. (Amorphous Cell builds cells according to a modified 

Markov process, incorporating rotational isomeric state probabilities modified to account for 

nonlocal [long-range] interactions [19, 20].) Eight different cells with an initial target density of 

0.9 g/cm3

 were built for each compound, the length of cube edges being ~25 Å for monochloride 

compounds and ~23 Å for monobromide compounds. A group-based cut-off method with tail 

correction was employed to evaluate nonbond interactions. The cut-off method assumes that the 

radial distribution functions converge to unity beyond the cut-off distance. The cut-off distance 

was specified to be 10 Å for all compounds except the CPAZ analogs, where a 10.5-Å cutoff was 

employed. 

The simulations consisted of three stages, the dynamics in all cases being modeled with Verlet 

velocity integration [21] and Andersen temperature control [22]. Berendsen pressure control 

[23] was employed for constant pressure simulations. The first stage was a 30,000-step, 

1-fs/step, constant volume and temperature (NVT) “pre-equilibration” simulation run to relieve 

large stresses (inadvertently) introduced by the cell packing procedure. The second stage of the 

procedure was a 30,000-step, 1-fs/step constant pressure and temperature (NPT) simulation that 

allowed the cell to equilibrate. The final stage was a 50,000-step, 1-fs/step NPT simulation 

during which data was recorded. 

Table 6 compares the densities of the monochloride analogs of DMAZ, CPAZ, MMAZ, and 

1-azidobutane vs. experimentally determined values for the corresponding azides. The 

computationally determined density for 1-chlorobutane is observed to be nearly identical to its 

experimentally determined value and that of 1-azidobutane. (Given that the COMPASS force 

field parameters for the atom types relevant to 1-chlorobutane were probably developed with a 
16

Table 6. Condensed-phase property estimates. 

Compound Density ∆Hv(298) ∆Hf(298) 

 MD Exp MD Exp Calc Exp Calc Exp 

 (g/cm3) (g/cm3) (kcal/mol) (kcal/mol) (kcal/mol) (kcal/mol) (cal/g) (cal/g)

1-azidobutanea 0.883 9.17 46.5 50.7 470 510 

1-chlorobutanea 0.882 ± 0.003 0.886 7.8 8.01 

1-bromobutanea 7.5 8.79 

2-azido-N-methylethanamine (MMAZ)b 0.970 69 690 

2-chloro-N-methylethanamine 0.980 ± 0.003 9.6 

2-bromo-N-methylethanamine 9.2 

2-azido-N,N dimethylethanamine (DMAZ)b 0.933 9.4 69 66 610 580 

2-chloro-N,N dimethylethanamine 0.955 ± 0.004 9.5 

2-bromo-N,N dimethylethanamine 8.8 

2-azido-N-cyclopropylethanamine (CPAZ)b 0.993 94 750 

2-chloro-N-cyclopropylethanamine 0.981 ± 0.006 9.1 

2-bromo-N-cyclopropylethanamine 9.7 

trans-2-chloro-N,N-dimethylcyclopropanamine (trans-ADMCPA analog)  

 1 enantiomer only 0.946 ± 0.006 

 Racemic mixture 0.953 ± 0.005 9.5 97 770 

cis-2-azido-N,N-dimethylcyclopropanamine (cis-ADMCPA analog)  

 1 enantiomer only 0.992 ± 0.006 

 Racemic mixture 1.000 ± 0.005 10.6 98 790 

Monomethylhydrazine (MMH)c 0.883 9.6 13.1 284 a

 Experimental data are from Lee et al. [16]. b

 Experimental data are from Thompson et al. [2, 3]. 

c

 Experimental data are as reported in the Schmidt [1] compendium. 

training set consisting of ω-alkylchlorides, the good agreement was expected.) The 

computationally determined densities for the monochloride analogs of MMAZ, DMAZ, and 

CPAZ are also observed to be in reasonable agreement with experimentally determined values 

for the corresponding azide. The approach predicts that the density of trans-ADMCPA will be 

0.945 g/cm3

, a value that is slightly lower than that predicted for DMAZ (0.955 g/cm3). The 

density of cis-ADMCPA is predicted to be 1.00 g/cm3

, a value that is even higher than that 

predicted for CPAZ (0.98 g/cm3

). 

Table 6 also presents estimates for the heats of vaporization of the monochloride and 

monobromide analogs of DMAZ, CPAZ, MMAZ, and 1-azidobutane. It is observed that the 

values for the monochloro and monobromo analogs of DMAZ and 1-azidobutane are similar to, 

but lower than, the values observed experimentally for the corresponding azides. Since the heats 

of vaporization determined for the monochloride and monobromide analogs are similar, the 

effort needed to perform a separate set of simulations with bromide analogs will not be 

undertaken in the future. Being a byproduct of simulations necessary to predict densities, the 

heats of vaporization derived from monochloride analogs are “free,” and thus provide an easily 

obtained reference point. In the present case, however, it is observed that most of the values in 

the table cluster near DMAZ’s experimentally determined value of 9.4 kcal/mol, and this value 
17

was employed by the author in calculating all of the condensed-phase heats of formation given in 

Table 6. The potential error associated with this approach is expected to be less than 

±2 kcal/mol. 

5. Ballistic Properties 

With estimates for condensed-phase heats of formation and densities, it is possible to calculate 

and compare the specific impulses (ISP) and density impulses (D*ISP) that MMAZ, DMAZ, 

CPAZ, and the ADMCPA isomers will produce when combined with an oxidizer. Table 7 

compares optimized ISP values from NASA-Lewis rocket calculations [24] for a system in which 

the oxidizer is an IRFNA “mixture.” (The oxidizer mixture is one employed by AMCOM for 

such comparisons.) It is observed that the optimized ISP values for the aliphatic amine azides are 

nearly identical to each other and less than 1% lower than the value obtained for MMH. 

Moreover, with higher densities than MMH, their D*ISP’s are predicted to be higher. 

6. Synthesis Possibilities 

The author has no (relevant) experience in the art of synthetic organic chemistry, but wanted to 

at least attempt to address the possibility of synthesizing ADMCPA. A literature search of 

synthesis routes for aliphatic amine azides revealed a large number of possibilities, with a 

relatively recent review of the preparation of azide compounds written by Schriven and Turnball 

being particularly instructive [25]. Of the approaches identified via this survey, the most 

intriguing to the author was suggested by the work of Benalil et al. [26]. Based on synthesizing 

desired 1,2 aminoazides by treating “appropriate” 1,2 aminoalcohols with triphenylphosphorous 

(PPh3), diethyl azodicarboxylate (DEAD), and HN3—i.e., the (modified) Mitsunobu reaction 

[27]—this approach should be readily testable because an appropriate 1,2 aminoalcohol for 

ADMCPA, namely trans-2-hydroxy-N,N-dimethylcyclopropanamine, has already been 

synthesized by Armstrong and Cannon [28]. Since the modified Mitsunobu reaction converts 

alcohols to azides through inversion of configuration, successful conversion of trans-2-hydroxyN,N-dimethylcyclopropanamine via this approach will probably produce cis-ADMCPA. 

7. Discussion 

The superior performance of hydrazine and its methylated derivatives compared to other 

hypergols can generally be attributed to three characteristics: short ignition delays, high 
18

Table 7. NASA-Lewis thermochemical code ISP and D*ISP predictions for 

various fuels.a

Compound O/F ISP %∆

 Throat Exit D*ISPb 

 (s) (s) (lbf · s/in3) 

2.0 112.9 284.8 

2.2 111.4 285.4 

2.4 109.9 284.4 10.1 +10 

2.6 108.5 281.0 

2.8 107.1 276.7 

MMAZ 

3.0 105.7 272.0 

2.0 113.7 281.1 

2.2 112.9 283.3 

2.4 111.7 284.4 9.8 +7 

2.6 110.4 284.4 

2.8 109.1 282.8 

DMAZ 

3.0 107.8 279.5 

2.0 113.9 281.3 

2.2 113.2 283.6 

2.4 112.0 284.8 

2.6 110.8 284.9 10.1 +10 

2.8 109.5 283.9 

CPAZ 

3.0 108.2 281.1 

2.0 114.3 282.5 

2.2 113.4 284.6 

2.4 112.3 285.6 

2.6 111.0 285.7 10.3 +12 

2.8 109.7 284.5 

cis-ADMCPA 

3.0 108.5 281.7 

2.0 114.2 282.1 

2.2 113.3 284.2 

2.4 112.2 285.3 

2.6 110.9 285.4 9.8 +7 

2.8 109.6 284.3 

trans-ADMCPA 

3.0 108.4 281.5 

2.0 115.6 284.7 

2.2 115.0 286.8 

2.4 113.9 288.0 

2.6 112.4 288.1 9.2 — 

2.8 110.9 285.7 

MMH 

3.0 109.5 280.8 a

 Results for “infinite-area” combustor problem with 2000-psia chamber pressure and 

equilibrium chemistry. The subsonic area ratio is 15.0, and the supersonic area ratio is 

14.175. 

b

 For consistency, in all cases (except MMH), the density predictions obtained via the 

molecular modeling computations are employed to calculate D*ISP. 
19

densities, and high specific impulses, the shortcoming of most alternatives being long ignition 

delays. Given that aliphatic azides are not hypergolic and that the ignition delays of aliphatic 

amines are much longer than those of hydrazine and its derivatives, the short ignition delays 

produced by (the aliphatic amine azide) DMAZ are surprising, and identifying the mechanisms 

that underlie this phenomenon could be useful in designing fuels with even shorter ignition 

delays. 

Since aliphatic azides are not hypergolic, but do undergo (explosive) exothermic unimolecular 

decomposition if raised to a sufficiently high temperature, and aliphatic amines are hypergolic 

but “slow,” in the absence of detailed knowledge about DMAZ’s molecular structure, a “working 

hypothesis” was suggested. That hypothesis was that exothermic proton transfer from nitric acid 

to the amine, which is more nucleophilic than the azide, was jump-starting the azide 

decomposition, and the azide decomposition was accelerating the otherwise slow secondary 

reactions involved in pure amine oxidation. This hypothesis was consistent with the observation 

of ammonium nitrate salts in combustion residue [3], and observed differences in the 

performance 2-azidoethanamines with different amine substituents, shorter ignition delays found 

for fuels whose amines would be expected to be stronger bases. Not surprisingly, this hypothesis 

led AMCOM to focus on synthesizing fuels with more a more nucleophilic amine. 

The genesis of this study was the finding that in DMAZ’s lowest energy configuration, the azide 

group sterically shields the lone pair electrons associated with the amine nitrogen [4]. Given the 

experimentally indicated importance of proton transfer to this site, the author initially assumed 

that shielding would reduce a compound’s reactivity and therefore contribute to increasing 

ignition delays. Thus, his interest was in identifying compounds that would prevent shielding. 

Through the course of this study, however, several observations led the author to consider the 

possibility that the amine-azide interaction in the shielding configuration is actually the enabling 

mechanism. First, given the fact that close to 50% of DMAZ’s amine sites will be shielded from 

proton attack at room temperature and that DMAZ is competitive with Aerozine 50, it would be 

imprudent to ignore this possibility. Second, though (aliphatic) azides are not known as 

hypergols, the azide group has two lone pair sites and nitric acid hydrogen bonds 

(exothermically) to these sites in the gas phase. Calculations for an as yet incomplete study to 

characterize DMAZ-nitric acid complexes indicate that hydrogen-bonding to azide sites is only 

slightly less than the exothermic than the hydrogen-bonding at amine sites. In addition, though 

enhancing the amine’s basicity would almost certainly reduce ignition delays, there is the 

potential that any increase in amine basicity will be offset by an enhancement of the amine-azide 

interaction and an increase in shielding. (Such an effect is suggested by preliminary results from 

ongoing theoretical characterizations of CPAZ and MMAZ.) If enhancement of the azide 

group’s basicity through the azide-amine interaction is the enabling mechanism, then cisADMCPA could yield very short ignition delays. The author hopes that the promise of the 

ADMCPA isomers that is indicated in the computational characterizations presented is sufficient 
20

to pursue their synthesis, as experimental testing with them should clarify the influence of the 

azide-amine interaction and the azide’s basicity on the ignition process. 

As a final note, the possibility of using a CH2 group to bridge the ethyl group carbons of DMAZ 

was investigated because of the obvious similarities between the 2-azidocycloalkanamines and 

DMAZ and CPAZ, but the bridge can presumably be made with groups other than CH2, NH and 

O being two possibilities. A stable structure based on the former—an aziridine—is shown in 

Figure 7. However, the author does not have enough knowledge of small heterocyclic organic 

compounds to even guess as to whether their properties will be similar to DMAZ or CPAZ, so he 

made no attempt to further characterize such alternatives. Certainly, property estimates for such 

alternatives could be calculated if considered warranted. 

Figure 7. An equilibrium 3-azido-2-dimethylaminoaziridine conformer. 

8. Summary 

Fuels based on 2-azidocycloalkanamines are proposed as means of obtaining hydrazinealternative hypergols with ignition delays shorter than those observed for DMAZ. The geometric 

parameters and normal modes for a number of 2-azidocycloalkanamines with C5H10N4

stoichiometry were characterized through the use of DFT, and MD simulations performed with 

the halogen analogs of ADMCPA, DMAZ, CPAZ, and MMAZ were employed to predict liquid 

densities and heats of vaporization. ISP and D*ISP values predicted based on the DFT and MD 

results, coupled with the possibility of shorter ignition delays, suggest that the ADMCPA 

isomers merit further consideration as alternatives to DMAZ or MMH in hypergolic propulsion 

system applications. 
21

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23

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Unsymmetrical Vicinal Diamines by Catalytic Hydrogenation or Reductive Alkylation With 

Dichloroboranes.” Tetrahedron, vol. 47, pp. 8177–8194, 1991. 

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24

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25

Appendix. Details From 2-Azido-N-methylcyclobutanamine (AMCBA) and 

2-Azidocyclopentanamine (ACPA) Theoretical Characterizations 

This Appendix provides tables summarizing the theoretical characterizations of cis and trans

forms of 2-azido-N-methyl-cyclobutanamine (AMCBA) and a trans isomer of 2-azidocyclopentanamine (ACPA). Table A-1 presents the geometric parameters for the AMCBA 

conformers shown in Figure 5, and Table A-2 presents their relative zero-point corrected 

energies, dipole moments, and rotational constants. Table A-3 presents the normal mode 

frequencies and integrated infrared (IR) intensities for transitions to these modes for the 

AMCBA structures. Table A-4 presents the geometric parameters for the ACPA conformer 

shown in Figure 6, and Table A-5 presents its normal mode frequencies and the integrated IR 

intensities for transitions to these modes. The dipole moment for the ACPA conformer is 

3.94 Debye, and its rotational constants are 3.07, 1.15, and 0.88 GHz. Its zero-point corrected 

energy is –415.448209 Hartrees. 
26

Table A-1. Geometric parameters for equilibrium AMCBA conformers as computed via 

B3LYP/6-311++G(d,p). 

 Conformersa

Parameter c-A c-B t-A t-D 

Bond Length (in Angstroms) 

N1-N2 1.136 1.135 1.135 1.136 

N2-N3 1.228 1.230 1.230 1.229 

N3-C4 1.475 1.471 1.469 1.474 

C4-C6 1.546 1.546 1.542 1.553 

H5-C4 1.095 1.095 1.097 1.095 

C6-C9 1.553 1.553 1.553 1.553 

H7-C6 1.089 1.089 1.090 1.090 

H8-C6 1.091 1.091 1.092 1.092 

C9-C12 1.550 1.546 1.570 1.549 

H10-C9 1.092 1.092 1.094 1.092 

H11-C9 1.091 1.091 1.090 1.090 

C12-C4 1.567 1.577 1.549 1.546 

H13-C12 1.105 1.103 1.094 1.103 

N14-C12 1.447 1.441 1.442 1.449 

H15-C14 1.016 1.012 1.015 1.015 

C16-C14 1.464 1.459 1.462 1.463 

H17-C16 1.093 1.094 1.094 1.092 

H18-C16 1.092 1.092 1.092 1.092 

H19-C16 1.103 1.103 1.102 1.102 

Simple Angles (in Degrees) 

N3-N2-N1 173.0 172.4 173.1 173.7 

C4-N3-N2 116.8 116.8 116.8 116.5 

H5-C4-N3 109.9 110.2 110.4 110.7 

C6-C4-N3 108.8 108.9 115.7 118.8 

H7-C6-C4 115.3 115.5 117.3 117.3 

H8-C6-C4 111.5 111.6 110.3 110.9 

C9-C6-C4 89.1 89.1 88.5 87.7 

H10-C9-C6 111.3 111.0 112.0 111.9 

H11-C9-C6 117.9 118.3 117.6 117.6 

C12-C9-C6 88.1 88.6 87.8 88.6 

H13-C12-C9 108.7 109.6 109.3 110.1 

N14-C12-C9 118.4 118.9 117.2 117.5 

H15-N14-C12 110.0 110.9 110.4 109.4 

C16-N14-C12 113.6 115.8 115.0 114.2 

H17-C16-N14 109.6 109.9 109.2 109.6 

H18-C16-N14 109.3 109.5 109.4 109.4 

H19-C16-N14 113.9 113.7 114.2 113.7 

Dihedral Angles (in Degrees) 

C4-N3-N2-N1 168.9 !166.3 174.4 !179.3 

H5-C4-N3-N2 !56.1 58.5 !36.8 42.4 

C6-C4-N3-N2 173.7 !171.1 164.2 !88.7 

H7-C6-C4-N3 24.2 !24.7 96.5 101.5 

H8-C6-C4-N3 149.7 !150.4 !29.2 !25.0 

C9-C6-C4-N3 !96.1 95.7 !142.0 !137.8 

H10-C9-C6-C4 92.1 !92.5 !92.1 !92.5 

H11-C9-C6-C4 !139.9 139.7 140.6 139.6 

C12-C9-C6-C4 !19.4 19.2 20.0 19.4 

H13-C12-C9-C6 !88.5 88.7 89.0 89.2 

N14-C12-C9-C6 140.9 !141.1 !141.5 !139.6 

H15-N14-C12-C9 !172.5 !30.2 49.2 !50.9 

C16-N14-C12-C9 64.5 !158.7 76.4 175.0 

H17-C16-N14-C12 !64.7 !65.2 !62.7 !64.4 

H18-C16-N14-C12 177.6 177.4 179.7 177.6 

H19-C16-N14-C12 56.2 55.8 58.2 56.0 

a

 Labels refer to Figure 5. 
27

Table A-2. Relative zero-point corrected energies, dipole moments, and rotational constants for 

equilibrium AMCBA conformers as computed via B3LYP/6-311++G(d,p). 

Conformer Designationa ∆E 

(kcal/mol) 

μ 

(Debye) 

Rotational Constants 

(GHz) 

trans conformers

t-A —b 3.54 2.24 1.15 0.80 

t-B 0.2 2.90 2.41 1.10 0.80 

cis conformers

c-A 1.2 3.25 2.10 1.43 0.92 

c-B —c 3.38 2.03 1.57 0.99 a

 See Figure 5. 

b

 Zero-point corrected energy is –415.414753 Hartrees. c

 Zero-point corrected energy is –415.410703 Hartrees. 
28

Table A-3. Harmonic vibrational frequencies and integrated IR intensities for equilibrium AMCBA 

conformers. 

Mode Conformera

c-A c-B t-A t-B 

ν A ν A ν A ν A 

1 58 0.2 64 0.1 35 0.2 27 0.0 

2 97 1.3 79 1.0 84 0.2 77 1.9 

3 105 0.5 104 1.0 106 0.7 116 1.7 

4 173 1.3 175 0.9 172 0.8 147 0.9 

5 192 0.4 183 0.6 197 0.4 190 0.1 

6 225 0.3 251 1.4 236 1.0 235 0.4 

7 298 1.7 273 2.9 278 4.2 332 1.9 

8 367 6.3 373 3.2 368 8.0 355 8.5 

9 439 5.7 417 4.0 449 3.1 419 5.5 

10 519 4.6 530 13.8 491 3.2 474 2.7 

11 559 12.0 559 16.0 548 5.1 547 8.8 

12 647 24.3 633 48.0 552 4.8 578 17.6 

13 699 2.0 667 21.1 680 39.8 672 7.9 

14 751 8.3 695 10.5 735 44.0 738 84.3 

15 777 59.0 755 1.0 818 19.5 811 3.0 

16 840 4.3 837 7.9 822 3.3 820 4.9 

17 905 5.7 903 3.1 909 5.5 924 3.1 

18 937 1.3 933 1.8 933 1.3 927 1.3 

19 950 8.4 962 2.8 991 12.0 997 38.2 

20 1004 6.4 996 4.3 1007 14.5 1007 0.1 

21 1041 18.1 1045 9.6 1050 16.3 1049 2.9 

22 1076 9.4 1078 8.6 1066 7.5 1078 11.9 

23 1116 5.6 1114 1.4 1102 12.4 1107 1.2 

24 1138 1.9 1143 4.0 1149 2.0 1146 2.0 

25 1173 13.3 1169 24.6 1162 38.2 1170 38.0 

26 1201 22.5 1187 11.4 1199 19.1 1207 1.8 

27 1212 1.1 1235 3.5 1211 2.9 1212 2.6 

28 1246 0.8 1248 0.7 1236 0.6 1242 0.2 

29 1266 1.1 1262 2.2 1252 0.3 1255 1.8 

30 1268 5.1 1272 9.8 1265 0.7 1263 2.0 

31 1294 6.4 1286 9.5 1280 15.3 1284 2.0 

32 1335 138.4 1332 123.6 1329 114.4 1329 135.3 

33 1344 65.9 1342 58.1 1356 64.1 1353 77.0 

34 1379 34.4 1383 22.3 1394 65.7 1402 55.0 

35 1459 2.0 1463 0.1 1458 1.9 1460 3.0 

36 1475 7.3 1472 4.3 1483 3.8 1474 3.1 

37 1480 2.6 1476 8.3 1491 14.6 1482 4.3 

38 1493 8.8 1493 8.4 1496 6.3 1493 5.1 

39 1496 6.4 1495 6.5 1506 9.1 1502 10.1 

40 1518 11.2 1517 12.7 1522 27.1 1518 13.4 

41 2231 609.7 2232 583.4 2233 684.5 2230 740.2 

42 2907 71.8 2935 36.2 2953 90.8 2937 41.4 

43 2938 114.2 2944 129.0 3009 19.0 2947 103.0 

44 3025 47.7 3026 45.3 3040 18.2 3041 14.6 

45 3059 7.7 3052 25.2 3050 23.3 3056 34.8 

46 3062 50.9 3053 34.4 3054 40.5 3062 35.5 

47 3068 31.2 3067 32.2 3065 25.3 3062 18.2 

48 3102 23.1 3100 24.7 3097 25.6 3102 29.7 

49 3111 16.3 3103 24.8 3102 26.2 3105 13.5 

50 3127 27.0 3126 24.7 3120 34.7 3120 34.3 

51 3506 0.2 3556 3.3 3516 0.4 3521 0.7 

a

 See Figure 5. 

Notes: ν = cm!1

; A = kilometers per mole.
29

Table A-4. Geometric parameters for an equilibrium ACPA 

conformer as computed via B3LYP/6-311++G(d,p). 

Parametera

Bond Length (in Angstroms) 

N1-N2 1.134 

N2-N3 1.230 

N3-C4 1.475 

H5-C4 1.010 

C6-C4 1.534 

H7-C6 1.091 

H8-C6 1.093 

C9-C6 1.557 

H10-C9 1.092 

H11-C9 1.092 

C12-C9 1.549 

H13-C12 1.097 

H14-C12 1.093 

C15-C12 1.543 

C15-C4 1.542 

H16-C15 1.096 

N17-C15 1.458 

H18-N17 1.013 

H19-N17 1.016 

Simple Angles (in Degrees) 

N3-N2-N1 172.2 

C4-N3-N2 117.0 

H5-C4-N3 109.4 

C6-C4-N3 110.4 

H7-C6-C4 111.9 

H8-C6-C4 108.2 

C9-C6-C4 105.6 

H10-C9-C6 111.8 

H11-C9-C6 110.3 

C12-C9-C6 105.9 

H13-C12-C9 110.5 

H14-C12-C9 113.2 

C15-C12-C9 105.1 

H16-C15-C4 112.0 

N17-C15-C4 111.9 

H18-N17-C15 111.6 

H19-N17-C15 112.8 

Dihedral Angles (in Degrees) 

C4-N3-N2-N1 168.3 

H5-C4-N3-N2 !38.2 

C6-C4-N3-N2 !160.0 

H7-C6-C4-N3 84.4 

H8-C6-C4-N3 !33.3 

C9-C6-C4-N3 !152.2 

H10-C9-C6-C4 !114.7 

H11-C9-C6-C4 126.9 

C12-C9-C6-C4 6.7 

H13-C12-C9-C6 !98.4 

H14-C12-C9-C6 141.7 

C15-C12-C9-C6 18.7 

H16-C15-C4-N3 46.4 

N17-C15-C4-N3 !70.7 

H18-N17-C15-C4 163.3 

H19-N17-C15-C4 !76.0 a

 See Figure 6. 
30

Table A-5. Harmonic vibrational frequencies and integrated IR 

intensities for an ACPA conformer as computed via 

B3LYP/6-311++G(d,p).a

Mode ν A 

1 40 0.2 

2 61 0.5 

3 114 0.3 

4 180 1.6 

5 231 29.0 

6 274 1.1 

7 354 7.4 

8 387 11.4 

9 469 4.0 

10 533 3.5 

11 556 9.3 

12 603 1.5 

13 691 11.8 

14 769 11.5 

15 796 75.4 

16 815 43.1 

17 910 4.4 

18 936 16.7 

19 956 3.6 

20 988 7.0 

21 1028 6.5 

22 1072 9.5 

23 1092 0.5 

24 1120 6.4 

25 1136 10.6 

26 1195 1.4 

27 1244 1.9 

28 1265 0.5 

29 1283 2.0 

30 1317 0.5 

31 1319 0.6 

32 1328 2.9 

33 1335 124.9 

34 1344 2.5 

35 1376 65.3 

36 1428 12.0 

37 1490 0.8 

38 1497 5.2 

39 1519 7.1 

40 1660 34.4 

41 2236 655.3 

42 2980 20.6 

43 3012 19.5 

44 3034 31.1 

45 3048 26.7 

46 3058 35.5 

47 3070 24.6 

48 3083 17.3 

49 3102 51.0 

50 3499 0.5 

51 3586 3.2 

a

 See Figure 6. 

Notes: ν = cu!1

; A = kilometers per mole.
31

hypergolic fuels, DMAZ, density functional theory, molecular dynamics, 36

 2-azidocycloalkanamines

The fuel 2-azido-N,N-dimethylethanamine (DMAZ) has shown considerable promise as a replacement for

hydrazine-based fuels in hypergolic propulsion systems, but the ignition delays observed for DMAZ-inhibited red

fuming nitric acid (IRFNA) systems are longer than those for monomethylhydrazine-IRFNA systems. This report

considers the potential of 2-azidodocycloalkanamine-based fuels for addressing this issue. Such molecules have two

stereochemically distinct isomers, one of which prevents the azide group from "shielding" the amine lone pair electrons

from proton attack. The other promotes such shielding. Since shielding likely influences the manner in which nitric

acid reacts with amine-azide fuels, the ignition delays for the isomers may be different, and it is possible that one of the

isomers will yield shorter ignition delays than DMAZ. To support consideration of the synthesis and development of

2-azido-N,N-dimethylcyclopropanamine (ADMCPA) equilibrium structures are identified and their gas-phase heats of

formations estimated via density functional theory-based calculations. In addition, ADMCPA isomer condensed-phase

densities and heats of vaporization are estimated via molecular dynamics simulations performed with halogen analogs. 

Combined and employed to predict ballistic properties, the computational results indicate that the ADMCPA isomers

merit further investigation as hypergols. A suggestion for synthesizing cis?ADMCPA is also proffered. 

ARL-TR-2806

U.S. Army Research Laboratory

ATTN: AMSRL-WM-BD

Aberdeen Proving Ground, MD 21005-5066

Michael J. McQuaid

Computational Characterization of 2-Azidocycloalkanamines: Notional Variations 611102.H43

on the Hypergol 2-Azido-N,N-Dimethylethanamine (DMAZ) 

September 2002 Final, May 2001–May 2002

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