bluuebunny/crossref_metadata_2025 huggingface dataset:
Proximity and the heteroatom effects on the carbon‐13 chemical shifts of methyl‐substituted phenols, anilines and thiophenols
Authors: Netzel Daniel A.
Published: May 2005

Upfield substituent‐induced 13C chemical shifts for aryl carbons of polymethyl substituted benzenes, phenols, anilines and thiophenols were investigated as a function of the proximity between substituents X and CH3 (X = CH3, NH2, OH and SH). The results indicate that the induced shifts of the substituted aryl carbons are, in general, independent of the polar substituent but depend on the number of adjacent substituted aryl carbons. A −2.0 ppm upfield shift was found for a substituted aryl carbon adjacent to one substituted aryl carbon and a −3.8 ppm upfield shift for a substituted aryl carbon bound by two substituted aryl carbons. It is suggested that the near additivity of the upfield shifts is the result of changes in the bond order between the aromatic ring carbons in the region of the substituted aryl carbons due to distortion of the ring. The 13C chemical shifts of the methyl substituents for methyl substituted phenols, anilines and thiophenols were determined, and it was found that the values could be predicted from the additivity parameters reported for the analogous methylbenzenes plus an additional pair‐interaction term associated with the through‐space electronic influence of the heteroatom.
ESR study of N‐acyl‐N‐alkyl nitroxide radicals from photolysis of N‐nitrosoamides
Authors: Flesia Elio , Surzur Jean‐Marie , Tordo Paul
Published: May 2005

A new method of generation of N‐acyl‐N‐alkyl nitroxide radicals by photolysis of N‐nitrosoamides is described. ESR parameters are reported for 17 radicals of the general formula RCON(R′)O.; the high resolution obtained allows conformational analysis which shows a preferred trans conformation around the CON bond and hindered rotation around the NR′ σ‐bond.
Long range substituent‐induced chemical shifts in the 13C NMR spectra of N‐benzylidenebenzylamines
Authors: Arrowsmith John E. , Cook Michael J. , Hardstone David J.
Published: May 2005

Carbon‐13 chemical shifts for N‐benzylidenebenzylamines are affected by substituents up to eleven bonds away from the substituent group. The data correlate well with Hammett constants.
Dynamic proton magnetic resonance studies on complex spin systems. Non‐mutual three‐spin exchange in four 1‐substituted cyclohexanes‐2,2,3,3,4,4,5,5‐d8 and mutual four‐spin exchange in cyclohexane‐1,1,2,2,3,3,4,4‐d8
Authors: Höfner Dieter , Lesko Susan A. , Binsch Gerhard
Published: May 2005

The intrinsic advantage proffered by coupled three‐proton spin systems in the quantitative study of conformational equilibria and equilibrations, as elaborated and exemplified in the preceding publication, is exploited for the determination of precise thermodynamic and dynamic parameters for octadeuteriocyclohexanes containing a cyano, chloro, bromo or deuteriomethoxy substituent and hydrogen atoms on the substituted and on one contiguous carbon. Dynamic quantities for the ring reversal of cyclohexane‐1,1,2,2,3,3,4,4‐d8, obtained by bandshape analysis of the deuterium‐decoupled proton NMR spectra broadened by mutual four‐spin exchange, are also reported. The measured standard entropy differences between the axial and equatorial conformational isomers of the monosubstituted cyclohexanes show that, in addition to the rotational entropy, there must be a significant contribution from the vibrational partition functions. The experimental activation entropies for the cyclohexane chair‐to‐twist‐boat conversion are at variance with conclusions drawn from naive symmetry considerations, but agree with the more sophisticated treatment of Pickett and Strauss; the data establish that there is virtually free pseudorotation in the transition states of the ring reversal for cyclohexane itself as well as for the monosubstituted derivatives studied in this investigation.
High resolution 13C NMR spectroscopy. IV—stereochemical assignments in butenedioic acids and 3‐pentene‐2‐ones
Authors: Braun S.
Published: May 2005

Vicinal 13C, H coupling constants 3J(CO, H) for butenedioic acids and 3J(CH3, H) for 3‐pentene‐2‐ones have been determined and are correlated with the configuration of the corresponding CC double bond. For both types the relationship 3J(CH) trans > 3J(CH)cis holds; in the case of the CH3, H couplings, however, the 3J(CH3, H) trans values are reduced because of steric reasons, so that configurational assignments seem possible only when both isomers are present. Additionally, the coupling constants 3J(COCH3,H) and the chemical shifts δ have been evaluated for the pentenones and it is shown that these parameters give information about the predominating conformation of α, β‐unsaturated methyl ketones.
Carbon‐13 NMR studies of substituted naphthalenes. I—complete assignments of the 13C chemical shifts with the aid of deuterated derivatives
Authors: Seita José , Sandström Jan , Drakenberg Torbjörn
Published: May 2005

Proton‐coupled as well as noise‐decoupled 13C NMR spectra of several substituted naphthalenes have been studied. Complete assignments of the 13C signals based on selectively deuterated derivatives and on the 13C1H coupling pattern have been made. For the methoxynaphthalenes, acetylnaphthalenes and naphthaldehydes the dominant conformations of the substituents have been deduced from the 13C chemical shifts.
Methyl substituent effects in the 13C spectra of cyclohexanone O‐methyl oximes and N,N‐dimethylhydrazones
Authors: Fraser Robert R. , Dhawan Kasturi L. , Taymaz Kevser
Published: May 2005

The 13C NMR spectra of a series of 4‐t‐butylcyclohexane‐O‐methyl oximes and N,N‐dimethylhydrazones containing α‐methyl substituents have been measured. The effects of α‐methyl substitution (syn‐axial, anti‐axial and anti‐equatorial) on the carbons α, β and γ to the substitution site are similar to those previously found in cyclohexanones. Use has been made of these substituent parameters to determine the conformational equilibria of the mobile 2‐methylcyclohexanone derivatives.
Ring conformations of 2‐substituted 2‐oxo‐4‐methyl‐1,3,2‐dioxaphosphorinanes. Evidence for a boat conformation in equilibrium with two interconverting chairs
Authors: Mosbo John A.
Published: May 2005

The 220 MHz proton NMR spectra of three isomeric pairs of 2‐R‐2‐oxo‐4‐methyl‐1,3,2‐dioxaphosphorinanes, where R = methoxy (1a, b), methyl (2a, b) and dimethylamino (3a, b) (a represents the trans and b the cis arrangement of R and the 4‐methyl group) were analyzed by iterative computer techniques. Ten ring conformations, two chairs, two half‐chairs and six boats were initially considered as being possible contributors to the overall solution conformations. Compounds 1a, 2a, 2b and 3b were all concluded to exist as single chair conformations with the 4‐methyl group equatorially oriented (eqch). In addition to 68% of compound 3a being in that eqch conformation, however, significant concentrations of the chair form containing an axially oriented 4‐methyl group (axch, 16%) and a boat conformation containing an equatorially oriented 4‐methyl group with phosphorus and C‐5 serving as the bow and stern (eq25, 16%) were also postulated. Similarly, it was suggested that 1b contained 60% eqch, 20% axch and 20% of the boat eq25. From the data for compounds 2a and b it was concluded that in the chair conformations of 2‐oxo species the phosphorus substituent orientation has little effect upon the 3J(POCH) coupling constants.
An application of 1H nuclear magnetic resonance to the determination of hydrophobic interactions in peptides
Authors: Kumar N. G. , Roeske R. W.
Published: May 2005

Intermolecular hydrophobic interactions between the indole or phenyl moieties of the peptides containing L‐tryptophan (L‐Trp) or L‐phenylalanine (L‐Phe) residues and the apolar isopropyl groups of the peptides containing L‐leucine (L‐Leu) or L‐valine (L‐Val) in aqueous solutions have been detected by 1H NMR by monitoring the observed changes in the proton magnetic resonance parameters of the methyl resonances of the peptides containing L‐Leu or L‐Val residues. The 1H NMR data indicate that intermolecular hydrophobic interactions are responsible for the observed changes in the proton magnetic resonance parameters of the methyl resonances. For example, when a solution of glycylglycylleucine (Gly‐Gly‐L‐Leu) in deuterium oxide was mixed with glycylglycyltryptophan (Gly‐Gly‐L‐Trp), the methyl protons of Gly‐Gly‐L‐Leu exhibited large diamagnetic ring current shifts. However, when glycylglycylglycine (Gly‐Gly‐Gly) was substituted for Gly‐Gly‐L‐Trp in the NMR experiment, the methyl resonances did not show any upfield or downfield shift, thereby demonstrating that the observed upfield shifts are not due to bulk susceptibility differences between solutions. The C‐terminus peptides containing L‐Leu or L‐Val residues bind to the aromatic L‐Trp or L‐Phe peptides better than the N‐terminus L‐Leu or L‐Val peptides. The C‐terminus Gly‐Gly‐L‐Leu binds better than the C‐terminus glycylglycylvaline (Gly‐Gly‐L‐Val). The strength and specificity of hydrophobic interactions in several small peptides are discussed.
Etudes Conformationnelles par Résonance Magnétique Nucléaire d'Ethanes Disubstitués par un Hétéroatome appartenant aux Colonnes IV, V et VI et par un Groupement Fonctionnel
Authors: Greiner J. , Rouvier E. , Pastor R. , Cambon A.
Published: May 2005

Dans ce travail, nous présentons les résultats obtenus dans l'analyse conformationnelle d'ethers, de sulfures, de sélénoéthers, d'amines, d'arsine, de germanes et de stannanes du type RXCH2CH2Y. La partie AA′BB′ (–CH2CH2–) des spectres a été analysée par une méthode basée sur les déplacements chimiques. Nous avons pu d'abord relier l'électronégativité de l'hétéroatome à la différence des déplacements chimiques des protons AA′BB′. Ensuite, une analyse conformationnelle par variation de température nous a permis de montrer que, dans le domaine étudié (230 K à 320 K), le triphénylstannyl‐3 propionitrile possède une structure ‘bloquée’.
Effect of paramagnetic anions on cations possessing stereochemically non‐equivalent methylene groups
Authors: Rosenthal Leslie , Walker Ian M. , Wiggins Don
Published: May 2005

A series of cations based on substituted pyrrolidines and piperidines has been investigated by NMR in low dielectric solvents. Non‐equivalent cation methylene protons are selectively shifted by paramagnetic anions; the size of the shift depends directly on the ability of the anion to approach closely the group in question. The assignments resulting from the shift data have been compared with the work of other authors.
A carbon‐13 NMR study of benzonorbornene isomers
Authors: Burn Peter K. , Crooks Peter A. , Meth‐Cohn Otto
Published: May 2005

The carbon‐13 NMR spectra of a series of exo‐and endo‐epimers of 2‐substituted benzonorbornene (2‐substituent = OH, OCHO, Br, NH2, NHMe or NMe2) have been examined. The spectra are readily assigned by comparison with the coupled and off‐resonance proton decoupled spectra as well as by the use of shift reagents. Interesting and diagnostic features of the spectra allow the distinction between epimers.
The carbon‐13 nuclear magnetic resonance spectra of anthraquinone, eight polyhydroxyanthraquinones and eight polymethoxyanthraquinones
Authors: Berger Y. , Castonguay A.
Published: May 2005

The 13C NMR spectra of anthraquinone, eight hydroxyanthraquinones and eight methoxyanthraquinones are reported. Peak assignment for the carbon atoms of these compounds is achieved by using decoupling techniques and by intercomparison of the variously‐substituted derivatives. Carbonyl chemical shifts in the hydroxyanthraquinones can be rationalized in terms of cross conjugation and intramolecular hydrogen bonding and in terms of cross conjugation in the methoxyanthraquinones. Hydroxy and methoxy substituent chemical shifts are also reported.
Elektronenstruktur und NMR‐Parameter von substituierten 5‐Phenyl‐2,4‐pentadiensäuren
Authors: Radeglia R. , Wolff R. , Spassov S. L. , Anghelova Y. , Ivanov Ch.
Published: May 2005

1H‐ und 13C‐NMR‐chemische Verschiebungen sowie vicinale HH‐Kopplungskonstanten von verschieden substituierten 5‐Phenyl‐2,4‐pentadiensäuren ArCHCHCRCRCOOH werden mitgeteilt und im Zusammenhang mit der Molekülstruktur diskutiert. Die entlang der Molekülkette alternierenden 13C‐chemischen Verschiebungen können linear mit den entsprechenden in PPP‐Näherung berechneten π‐Elektronenladungsdichten korreliert werden. Die ebenfalls alternierenden Einflüsse der paraständigen Substituenten bzw. der Lösungsmittel auf die 13C‐chemischen Verschiebungen sind mittels Atom–Atom‐Polarisierbarkeiten beschreibbar.
Carbon‐13 NMR spectra of some 8,13‐diazasteroids and related model isoquinolines
Authors: Verchère Catherine , Rousselle Dominique , Viel Claude
Published: May 2005

Carbon‐13 NMR spectra of some dihydro‐ and tetrahydro‐isoquinolines were studied and applied to the assignments of 13C NMR signals of some 8,13‐diazasteroids related to the estrone series. Some deuterated compounds were also examined. All signals could be assigned and an important long‐range isotopic effect was observed which seems to be due to an interaction between the CH(D) bond and the nitrogen lone pairs.
Lanthanide shift reagents. IX. Proton and carbon magnetic resonance study of specific contact interactions of a bifunctional oxazole amide with fluorinated lanthanide shift reagents
Authors: Rackham David M. , Cockerill Anthony F. , Harrison Roger G.
Published: May 2005

Highly specific proton line‐broadening and paramagnetic 13C shifts observed for N‐butyl‐N(4‐methyloxazol‐2‐yl)‐2‐methylpropionamide in the presence of fluorinated lanthanide shift reagents, are absent when non‐fluorinated reagents are used. This unusual behaviour is rationalized in terms of possible chelation of the N‐butyl‐N(4‐methyloxazol‐2‐yl)‐2‐methylpropionamide to the lanthanide reagent, causing transfer of the unpaired electron into the heterocyclic ring.
The 13C NMR spectrum of abietic acid and its methyl ester
Authors: Smith William B.
Published: May 2005

The assignment of lines in the 13C NMR spectrum of abietic acid and its methyl ester have been made using carbon T1 values and lanthanide induced shift effects. Structure–NMR parameter values are briefly discussed.
1H and 13C NMR spectra of new 2‐thiabicyclo[3.2.0]hept‐3‐enes
Authors: Kalabin G. A. , Trofimov B. A.
Published: May 2005

Three new compounds, one with the molecular formula C6H8S and two corresponding to C7H10S have been isolated together with the main product, divinyl sulphide, from the reaction products of acetylene with sodium sulphide. Structure determination through 1H and 13C NMR with selective 13C{1H} decoupling, showed C6H8S to be a new heterocyclic compound, 2‐thiabicyclo[3.2.0]hept‐3‐ene, and the two C7H10S compounds its exo‐ and endo‐6‐methyl derivatives. Since the spectral parameters of these heterocycles were not known, all possible structures corresponding to the molecular formulae were considered.
The torsional barrier in aromatic carbonyl compounds. VI. Carbon‐13 and 1H DNMR study of protonated alkyl and haloalkyl p‐tolyl ketones
Authors: Barthelemy Jean‐Françlois , Jost Roland , Sommer Jean
Published: May 2005

The free energy of activation of the torsional barrier around the phenyl–carbonyl bond in a series of stable protonated α‐substituted p‐methylacetophenones (p‐tolyl‐ where R = CH3, C2H5, i‐C3H7, t‐C4H9, CH2Cl, CHCl2, CCl3, CH2F, CHF2, CF3 and CH2Br) has been evaluated by complete lineshape analysis of 13C or proton low temperature NMR spectra. α‐Substitution by an alkyl group leads to a decrease of the barrier height due to both steric and electronic effects. For the halo compounds, steric and electronic effects of the substituents are in competition, leading to a very high ΔG≠ value in protonated α,α,α‐trifluoro‐p‐methylacetophenone (63.2 kJ mol−1). In addition, the twist angle of the protonated carbonyl group has been tentatively evaluated by the use of the (modified) Stothers's method.
Application of selective 13C{1H} nuclear overhauser effects with low‐power 1H irradiation in carbon‐13 NMR spectroscopy
Authors: Uzawa Jun , Takeuchi Setsuo
Published: May 2005

The feasibility of the application of selective 13C{1H} nuclear Overhauser effect (NOE) measurements to organic structural analysis in 13C NMR spectroscopy has been investigated at 25 MHz using citraconic anhydride and the methyl ester of pentalenolactone as model compounds. This selective 13C{1H} NOE technique with single frequency low‐power 1H irradiation should find wide application in the structural elucidation of organic compounds, especially for the reliable assignment of quaternary carbon signals.
INDO/S parameterized calculations of some 13C nuclear screening data
Authors: Jallali‐Heravi M. , Webb G. A.
Published: May 2005

Nuclear screening tensors, their anisotropies and 13C chemical shifts are calculated for a number of carbon environments and compared with the corresponding experimental data. The agreement found with the experimental results is an improvement over that obtained from CNDO/S parameterized calculations. The improvement stems from the inclusion of the one‐centre exchange integrals, which results in smaller values for the excitation energies from the INDO/S calculations. It is demonstrated that a linear relationship between 13C chemical shift and the lowest energy transition is not to be expected. The average values of the excitation energies of the various transitions contributing to the 13C screening are found to have significant variations.
Carbon‐13 NMR spectra of some chlorinated polycyclodiene pesticides
Authors: Cox Richard H. , McKinney James D.
Published: May 2005

Carbon‐13 NMR spectra have been obtained for aldrin, dieldrin, isodrin, endrin, heptachlor, heptachlor oxide and 24 of their degradation/conversion products. Chemical shifts were assigned on the basis of (1) comparison among the spectra, (2) single frequency, off‐resonance decoupling experiments, (3) substituent effects derived for norbornanes and (4) spectra obtained with an added lanthanide shift reagent. The substituent effects previously reported for norbornanes were found to be applicable for establishing trends in the chemical shifts for many of the compounds studied.
Stereochemical assignment at the C‐13 carbon of pimaradienes by 13C NMR. A reassessment
Authors: Beier Ross
Published: May 2005

According to reported results by Kato et al. in their 1977 paper, 13C data can not be used for assignment of stereochemistry at carbon‐13 in pimaradiene‐type compounds. By comparing well established 13C trends to the appropriate conformations, one can indeed predict the correct stereochemistry at C‐13 of pimaradienes. The result by this method correlates exactly with crystal structure data. 13C NMR is reliable for determination of C‐13 stereochemistry in the pimaradienes.
Additivity of proton and carbon nmr chemical shifts in protonated benzene carboxylic acids
Authors: Bruck Daniel , Rabinovitz Mordecai
Published: May 2005

The additivity of the proton and carbon chemical shift increments due to structural changes in a series of conjugate acids derived from benzene polycarboxylic acids is reported. In the acids, two sets of increments had been applied, one to the ortho diacids and one to acids which do not bear ortho substituents. In the conjugate acids only one set of increments is required. The disappearance of the ‘ortho’ effect may be the outcome of properties inherent to these conjugate acids.
Nitrogen‐15 nuclear magnetic resonance spectroscopy. Pyridine N‐oxides and quinoline N‐oxides
Authors: Yavari Issa , Roberts John D.
Published: May 2005

The noise‐decoupled nitrogen‐15 NMR spectra of ten pyridine N‐oxides and two quinoline N‐oxides have been obtained at the natural‐abundance level by high‐resolution NMR spectroscopy. Substituents at the 4‐ring position of pyridine N‐oxide, capable of resonance interaction with the N‐O moiety, give fairly large shifts in the expected directions. Spectra taken in dimethyl sulfoxide solution give 5–20 ppm and 33–55 ppm downfield shifts with respect to the solutions of the same substances in 2,2,2‐trifluoroethanol and trifluoroacetic acid. Solvent influences are discussed in terms of hydrogen bonding and protonation of the N‐oxide oxygen. Carbon‐13 chemical shifts and one‐bond carbon‐hydrogen coupling constants of some substituted pyridine N‐oxides are reported and discussed.
Detection of halogen bond formation by correlation of proton solvent shifts. 1. Haloforms in n‐electron donor solvents
Authors: Bertrán José Fernández , Rodríguez Mario
Published: May 2005

The solvent shifts of haloformic protons, (Cl3CH, Br3CH, I3CH), have been measured in 24 n‐electron donor solvents consisting of halogenated hydrocarbons, esters, ketones, ethers and amines. Deviations of ΔBr and Δ1 from linear dependence with ΔCl are indicative of the presence of halogen bond formation competitive with hydrogen bonding interactions. Bromoform interacts predominantly by hydrogen bonding, halogen bonding being detected to a small extent in chlorinated hydrocarbons and amines. Iodoform shows halogen bonding interactions which increase in relative importance to hydrogen bonding with solvent basicity. Halogen bonding is predominant for solutions of iodoform in amines.
Über Zuordnungsprobleme von 13C‐Signalen in den NMR‐Spektren von Benzheteroazolen
Authors: Gründemann E. , Martin D. , Wenzel A.
Published: May 2005

Für verschiedene Benzimidazol‐ und Benzoxazolderivate wurden die chemischen Verschiebungen im 13C‐NMR‐Spektrum bestimmt. Mit Hilfe von Additivitätsparametern lassen sich die 13C‐Signale der Benzokohlenstoffatome in unsymmetrischen Benzheteroazolen bestimmen. Die Struktur der Reaktionsprodukte aus Benzimidazolin‐ und Benzoxazolin‐thion‐(2) und Arylcyanaten werden abgeleitet.
Substituent Conformational effects in vicinal 13C13C spin–spin coupling constants
Authors: Marshall James L. , Faehl Larry G. , Kattner Richard , Hansen Poul Erik
Published: May 2005

A series of 7‐13C‐labeled o‐substituted toluene derivatives and carboxyl‐13C‐isocrotonic and crotonic acid were synthesized and studied by 13C NMR spectroscopy to obtain 13C13C spin‐spin coupling constants involving the labeled carbon. The cis 3J(CC) values were different from those in previous studies in that these J(CC) values were relatively small and the usual dependence of 3J(CC) on the s‐character of the terminal carbon was reversed. Further, a strong dependence of 3J(CC) on the conformational orientation of a terminal carbonyl group was shown to exist. Through‐space interactions of the two coupling carbons were shown to contribute to these ‘anomalous’ results, and thus it was shown the cis carbon‐carbon couplings may not be directly related to geometrically equivalent proton‐proton couplings, as are other carbon‐carbon couplings.
A study of the use of MINDO/3 parameters in calculations of carbon and nitrogen screening constants
Authors: Jallali‐Heravi M. , Webb G. A.
Published: May 2005

The calculation of some carbon and nitrogen screening constants and chemical shifts is reported. The independent electron theory developed by Pople is used as the basis of the calculations. Within this framework the MINDO/3 parameterization scheme is employed and shown to provide quantitatively unreliable results. Improved agreement with the experimental data is found when the electronic excitation energies are taken from INDO/S parameterized calculations. The relative lack of success achieved by the MINDO/3 calculations is probably a reflection on the inability to reproduce the electronic excited states satisfactorily.
Comparison of steric effects on 31P chemical shifts in some 7‐norbornyl, 7‐norbornenyl and cyclohexyl phosphorus compounds
Authors: Littlefield Lory B. , Quin Louis D.
Published: May 2005

Phosphorus‐31 NMR spectra were obtained on both syn and anti isomers of norbornenes with the 7‐position bearing Cl2P‐, Me2P‐, Me2(S)P‐ and Me3P as substituents. Norbornanes with 7‐Cl2P‐ and 7‐Me2P‐ were also studied. Just as is true for 13C shifts for 7‐Me in these bicyclo[2.2.1]heptane derivatives, the 31P shifts all fall noticeably upfield of published values for comparable cyclohexane derivatives. Consistent also with the 13C effect, a slight shielding of 31P in Me2P‐ (1.1 ppm) was noted when this group was syn to the double bond of the norbornene system, relative to the value for the anti compound, suggesting the sensitivity of 31P to a diamagnetic effect from the double bond. However, the more space‐demanding Cl2P group when moved from the crowded anti to the less crowded syn position experienced a strong deshielding effect, as did the Me2(S)P‐ and Me3P‐ groups. The opposite is seen when these same groups are moved from the crowded axial to the less crowded equatorial position of cyclohexane, and a new structural influence appears to be operating in this system. A recent proposal that steric compression causes bond angles about phosphorus to increase and that this is the cause of the γ‐shielding effect is not supported by published NMR and X‐ray structural data for cis‐ and trans‐1‐methyl‐4‐tert‐butyl‐4‐phosphorinanol. Bond angles about phosphorus are virtually identical in these isomers, yet 31P shifts differ by 6.9 ppm.
Specific deuteration effects on carbon‐13 NMR relaxation data of amido‐type systems
Authors: Shapiro M. J. , Kahle A. D.
Published: May 2005

The effect of deuterium substitution in amido‐systems is explored. For benzamide, both positive and negative changes in TDD1 are observed. A method for structure elucidation of these and related systems is presented.
A 13C{1H} double resonance study of the signs of 1H19F and 13C19F spin coupling constants in fluorobenzenes and 2‐fluoropyridine
Authors: Brey W. S. , Jaques L. W. , Jakobsen H. J.
Published: May 2005

The signs of all 13C19F and 1H–19F coupling constants in fluorobenzene, some substituted derivatives, and in 2‐fluoropyridine have been related using single‐frequency 13C{1H} double resonance techniques. All 13C19F couplings in these compounds are shown to be positive. Direct experimental proof is given for a positive sign for the small five‐bond 1H19F coupling constant (=0.2—0.3 Hz) in fluorobenzene. The positive sign for 4J(C‐4, F) in fluorobenzene is in accord with a positive π‐electron contribution to this coupling.
13C nuclear magnetic resonance spectroscopy of selected adenine nucleosides: Structural correlation and conformation about the glycosidic bond
Authors: Akhrem A. A. , Mikhailopulo I. A. , Abramov A. F.
Published: May 2005

Structural correlations have been carried out from 13C chemical shifts (δ) and by analysis of 1J(CH) coupling constants, and the conformation about the glycosidic bond has been studied by means of the 3J(CH) vicinal coupling constants between C‐8 and H‐1′ of some adenine nucleosides such as adenosine (Ado), N(7)‐β‐D‐ribofuranosyladenine (N(7)‐Ado), N(9)‐ and N(7)‐β‐D‐xylofuranosyladenine (N(9)‐xylAde and N(7)‐xylAde), N(9)‐(3‐chloro‐3‐deoxy‐β‐D‐xylofuranosyl)adenine (3′‐Cl‐xylAde) and N(9)‐(2‐chloro‐2‐deoxy‐β‐D‐arabinofuranosyl)adenine (2′‐Cl‐araAde). The analysis of the influence on δ13C of the nature and configuration of the substituent in the carbohydrate fragment of the molecule has revealed two types of effects, namely, 1,2‐cis and 1,2‐trans. This approach, as well as the 3J(CH) values and the analysis of the C‐3′‐endo⇌C‐2′‐endo equilibrium of the carbohydrate fragment of nucleosides, and circular dichroism (CD) data, provides important information on the conformation about the glycosidic bond. The magnitudes of 3J(C‐4, H) are indicative of the position of attachment of the carbohydrate fragment to the heterocyclic base.
Quantitative analysis of a mixture of cresols by carbon‐13 NMR spectroscopy
Authors: Chiang Hung‐Cheh , Lin Long‐Jin
Published: May 2005

The suitability of 13C NMR as a technique for determining o‐, m, and p‐cresols in their mixtures was investigated. Spectra were determined in methanol, containing o‐toluidine as an internal standard, without nuclear Overhauser suppression. Ratios of peak areas of each cresol isomer to o‐toluidine were determined by means of the standard calibration method, and then mixtures of cresol isomers were prepared and quantified in varying concentrations from 8.30 to 66.84 mol% for each isomer, with an average absolute error of 0.78% for all isomers. The method described was convenient and the results were generally satisfactory.
NMR Studies of ortho and meta‐ fluorocinnamate‐α‐chymotrypsin complexes
Authors: Gerig J. T. , Halley B. A. , Loehr D. T. , Reimer J. A.
Published: May 2005

Fluorine magnetic resonance spectroscopy has been used to examine the complexes formed between o‐ and m‐fluorocinnamate ions and the enzyme α‐chymotrypsin. Study of the frequency dependence of fluorine spin‐lattice and spin‐spin relaxation rates suggests that, like the p‐isomer, both the o‐ and m‐fluorocinnamates bind equally well to monomeric, dimeric and trimeric forms of the protein. Dipole‐dipole interactions with protons of the enzyme play an important role in relaxing the protein‐bound fluorine nucleus. Various deuterated forms of the ortho isomer were used to obtain evidence suggesting that the conformation of this molecule bound to the enzyme is similar if not identical to the conformation found in free solution. NMR methods were used to estimate the rates of dissociation of the complexes and the chemical shifts of the bound fluorine atoms were determined to be substantially downfield of their positions in the absence of enzyme.
A 13C NMR study of pyridoxal‐5′‐phosphate oxime
Authors: Korpela Timo , Lundell Juhani , Mäkinen Eila
Published: May 2005

Pyridoxal‐5′‐phosphate amino‐oxy acetate oxime was titrated in water, over the pH range 4–12, and the changes followed using 13C NMR. The results were compared to those of analogous Schiff's bases presented in the literature. The chemical shifts and titration curves of the oxime were appreciably different from those of the Schiff's bases, and the differences are explained as being due to the absence of ketoenamine‐enolimine tautomerism in the oxime. The low chemical shift value and the large changes of the oxime azomethine carbon during titration, as compared to the Schiff's bases, are discussed. The high stability of the oximes in water makes them suitable as model compounds for some tautomeric forms of the Iess stable Schiff's bases.
Selenium‐77 chemical shifts of cyclodiphosphazane selenides
Authors: Keat R. , Rycroft D. S. , Thompson D. G.
Published: May 2005

Isomeric cyclodiphosphazane selenides, R(X)P(NBu1)2P(Y)R (R=OMe or NMe2, X=Se, Y=lone pair; R=OMe or NMe2, X=Y=Se) display large differences (34–122 ppm) in 77Se chemical shift. The 77Se shifts of these and related amino derivatives are well to low field of the 77Se shifts of analogous acyclic phosphorus selenides.
Effets de Solvant Aromatique en Résonance Magnétique Protonique des Stéroïdes Hydroxylés
Authors: Genard P.
Published: May 2005

L'hydroxylation de stéroïdes saturés tels que l'androstane et le prégnane entraîne un effet de solvant aromatique appréciable au niveau des protons des méthyles angularies 18‐H et 19‐H.

Les déplacements chimiques associés à plusieurs hydroxyles ou à des hydroxyles et des cétones, sont en général approximativement additifs.
Aziridines N‐Non substituées. Détermination des Paramètres Thermodynamiques ΔG°, ΔH°, ΔS° Liés à l'Equilibre Conformationnel à partir de Mesures RMN 1H à Haut Champ
Authors: Lopez A. , Gauthier M. M. , Martino R. , Lattes A.
Published: May 2005

Bien que le phénomène d'inversion de l'azote dans les aziridines secondaires ait pu être mis en évidence par RMN 1H, seule une étude systématique à 250 MHz a permis d'étudier quantitativement la répartion des deux invertomères et ainsi, de déterminer les paramètres thermodynamiques liés à l'équilibre conformationnel. Ces paramètres ont été déterminés pour 32 composés. Dans les aziridines C‐phénylées, une variation de l'encombrement du groupement aromatique en fonction des autres substituants du cycle aziridine peut être mis en évidence. Ces observations prouvent l'existence d'un phénomène de conjugaison entre système aromatique et petit cycle. phénomène préalablement mis en évidence par effet Faraday.
1H NMR studies of intramolecular hydrogen bonding in N‐(pyridyl)amides of 6‐methylpicolinic acid N‐oxide
Authors: Brzezinski Bogumil
Published: May 2005

The 1H NMR spectra of seven N‐(pyridyl)amides of 6‐methylpicolinic acid N‐oxide in chloroform were obtained. The influence on the chemical shifts of the NH protons of temperature, concentration and the CH3 substituent in the pyridine ring was studied. The NH protons were found to be shifted to low fields (∼14 ppm) owing to the formation of strong intramolecular hydrogen bonding. The influence of the pyridine ring on the chemical shift of the NH proton is comparable with the inductive effect of the p‐nitrophenyl group. The hindered rotation around the N‐pyridyl bond of N‐(α‐pyridyl)amides of 6‐methylpicolinic acid in solution is discussed.
A 1H NMR study of the tropylium ion, partially oriented in a lyotropic solvent
Authors: Diehl P. , Jokisaari J. , Dombi G.
Published: May 2005

The 1H NMR spectrum of tropylium fluoroborate dissolved and oriented in a lyotropic decyl sulphate phase has been recorded and analysed. Direct as well as indirect HH coupling constants have been obtained. The vibrationally uncorrected proton skeleton structure deviates slightly from a regular heptagon. The deviations are between two and three times larger than those of benzene from a hexagon, previously observed in the same solvent.
Analyse Conformationnelle par RMN du Proton des Oxo‐2 Oxathiazannes‐1,2,3 (Sulfinamates Cycliques) Diversement Substitués en 3, 4 et 6
Authors: Tisnès P. , Maroni P. , Cazaux L.
Published: May 2005

Cette étude menée sur seize composés montre qu'en l'absence des substituants sur les carbones en 4,5 et 6, la forme chaise à groupe SO axial (CA) est la plus stble d'au moins 8,4 kJ mole−1, comme dans le cas des sulfites cycliques correspondants. Lorsqu'il y a des substituants méthyles ou tertiobutyles en 4 et 6, la conformation dépend de leur orientation par rapport au groupe SO, ainsi que de la nature du substituant sur l'atome d'azote. Pour les configurations trans, la conformation reste chaise CA anancomère, sauf lorsqu'il existe des interactions gauches importantes: pour le tert‐butyl‐3 méthyl‐4‐t‐oxo‐2‐r oxathiazanne‐1,2,3 la forte interaction gauche Me/tBu conduit à une conformation croisée d'axe‐3,6 à SO axial (CNA). Lorsqu'un des substituants en 4 et 6 est cis, la conformation du sulfinamate peut être soit chaise à SO axial (CA) si c'est un méthyle en 4, même avec un tertiobutyle en 3 qui serait alors axial, soit croisée d'axe‐1,4 à SO axial (COA) si c'est un tertiobutyle. Contrairement aux sulfites cycliques, les formes chaises à SO équatorial (CE) et croisée d'axe‐2,5 à SO isoclinal (CS, CS′) sont l'exception et ne sont rencontrées qu'au sein d'équilibres conformationnels.
Etude des Dérivés de la Vitamine B6. Conformation des Complexes de Lanthanides avec le Pyridoxal‐5′‐phosphate et la Pyridoxamine‐5′‐phosphate en Phase Aqueuse à pD = 1,3
Authors: Asso M. , Asso L. , Mossoyan J. , Benlian D.
Published: May 2005

Une méthode de traitement de données de déplacements paramagnétiques des résonances 1H et 13C permet d'établir l'analyse conformationnelle de molécules flexibles coordinées aux cations de lanthanides. Les exemples du pyridoxal 5′‐phosphate (PLP) et de la pyridoxamine 5′‐phosphate (PMP) en solution aqueuse, à pD = 1,3, ont été traités. Dans les deux cas, la rotation autour de PO‐5′, est une rotation empéchée avec une distribution gaussienne autour de la valeur la plus probable. Les valeurs des angles et des distances entre la cation de terre rare et les noyaux du ligand sont déterminées.
On the assignments of carbon‐13 NMR spectra of cyclic nucleotides
Authors: Kainosho M.
Published: May 2005

Two conflicting assignments have been proposed for the 13C NMR signals of 3′,5′‐cyclic nucleotides. This communication describes selective decoupling experiments for several cyclic nucleotides which provide the correct assignment based on unambiguous experimental evidence.
RMN du 13C de Composés Méthylés Soufrés
Authors: Dauphin G. , Cuer A.
Published: May 2005

Une étude par spectroscopie 13C d'une série de composés méthylés soufrés est réalisée. Les effets des fonctions soufrées –SH, –SMe, –SSMe, –SSEt, –SSMe, –SC(O)Me, –SC(S)Me sur le déplacement chimique du carbone méthylique sont examinés. Les déplacements chimuques 13C d'une série de thio et dithioesters méthyliques aliphatiques sont comparés à ceux des esters correspondants et reliés aux propriétés chimiques.
Etude en Résonance Magnétique Nucléaire du Carbone‐13 de Quelques Aminopyrazoles. Sur le Problème de la Détermination des Constantes d'Equilibre Tautomère
Authors: Gonzalez Emmanuel , Faure Robert , Vincent Emile‐Jean , Espada Modesta , Elguero José
Published: May 2005

Les déplacements chimiques du 13C de trente‐deux pyrazoles ont été mesurés dans le diméthylsulfoxyde hexadeutérié et l'hexaméthylphosphorotriamide. Nous avons déterminé l'influence respective des différents substituants par régression multilinéaire (substitutions par un méthyle et un amino sur les carbones de l'hétérocycle, et par un méthyle, un n‐butyle et un phényle sur l'azote). Le problème de la détermination des constantes d'équilibre tautomère, à partir des résultats de la RMN du 13C est discuté et illustré avec le cas des amino‐3(5) pyrazoles.
Nuclear magnetic resonance of 1,4‐benzodiazepines. II Stereochemistry of 1,3‐dihydro‐2H‐1,4‐benzodiazepin‐2‐ones by lanthanide shift reagents
Authors: Romeo G. , Aversa M. C. , Giannetto P. , Vigorita M. G. , Ficarra P.
Published: May 2005

The sterochemistry of some 1,3‐dihydro‐2H‐1,4‐benxodiazepin‐2‐ones, employed as psychotherapeutic agents, is deduced by proton magnetic resonance using the paramagnetic shift reagent Eu(fod)3. the lanthanide induced shifts are computer simulated on the basis of the geometric parameters of the protons in different model structures, having intermediate conformations between a cycloheptadiene‐ and a cyclohepatatriene‐like system. N‐Desmethyldiazepam shows a conformational equilibrium between two pseudoboat forms, while the 1‐alkyl substituted derivatives exist, at room temperature, in olny one boat cycloheptatriene‐like conformation.
Some observations on the NOE effect in 1H NMR spectroscopy
Authors: Schilling Gerhard , Klosterhalfen Bernd
Published: May 2005

The NOE enhancement factor in 1H NMR spectroscopy is shown to be a function of dipole‐dipole interaction of the solute. The NOE increases with increasing concentration if a monomer‐dimer equilibrium exists in solution.
15N NMR spectroscopy 12:—steric effects in diastereomeric oligopeptides of alanine, phenylalanine and valine
Authors: Kricheldorf Hans R. , Hull William E.
Published: May 2005

Eight pairs of diastereomeric di‐, tri‐, and tetrapeptides were prepared from alamine, phenylalanine, valine and glycine. Their natural abundance 15N NMR spectra were measured in a 1:1 mixture of acetone/dimethyl sulphoxide and in all eight cases the diastereomers could be distinguished without the aid of shift reagents. The shift difference between the signals of diastereomers is dependent on the nature of the amino acid and on the solvent.
1H NMR studies of phenylazo‐alkenes. Proton shielding increment values for the s‐trans‐(E)‐phenylazo substituent
Authors: Schantl Joachim
Published: May 2005

The additive proton shielding increments for the s‐trans‐(E)‐phenylazo substituent have been evaluated from the 1H NMR spectra of a number of phenylazo‐alkenes. Deviations from additivity are indicative of a different stereochemistry of the azo‐ene system.
Calculation of some 13C chemical shifts for compounds containing cumulative double bonds. The allene, ketenimine and carbodiimide series
Authors: Collier C. , Webb G. A.
Published: May 2005

Calculations based on Pople's independent electron model, with CNDO/S and INDO/S parameterizations, are reported for some ketenimines and carbodiimides. The unusually large shielding of the central carbon uncleus is accounted for by means of the various electronic transitions which contribute to the paramagnetic shielding term. Changes in carbon charge densities tend to predict a chemical shift trend opposite to that observed.
1H‐ und 13C‐NMR‐Untersuchungen zur Struktur N‐substituierter Tetrazole—Die Strukturen des N‐Methoxycarbonyl‐, N‐Acetyl‐ und N‐(Tri‐n‐butylstannyl)‐tetrazols sowie Substituenteneffekte auf δ13C und 1J(CH)
Authors: Könnecke Andreas , Kleinpeter Erich
Published: May 2005

Die 1H‐ und 13C‐NMR‐Spektren einiger isomerer N‐substituierten Tetrazole wurden untersucht. Zur Unterscheidung der strukturisomeren N‐substituierten Tetrazole sind die 13C‐NMR‐Spektren besser geeignet, eine Ausnahme sind Derivate mit elektropositiven Substituenten wie SnBu3. Korrelationen von δC‐5 (invers) und 1J(C‐5,H) mit σ1 bei 1‐substituierten Tetrazolen erlaubten die Strukturzuodnung des N‐SnBu3‐ Derivates als 1‐(Tri‐n‐butylstannyl)tetrazol. Die chemische Verschiebungsdifferenz der Phenylkohlen‐stoffatome ΔC′ = δC‐3′—δC‐2′ ist kein signifikantes Struktur‐ und Konformationskriterium für N‐substituierte 5‐Phenyltetrazole; aussagekräftiger scheint ΔH′ der 1H‐NMR‐Spektren zu sein.
The alkali cation effect on the 1H NMR chemical shifts of the indenyl carbanion
Authors: Gooijer C. , Velthorst N. H.
Published: May 2005

The complex character of the temperature dependence of the 1H NMR chemical shifts of indenyl‐lithium and ‐sodium in dimethoxyethane is explained. It is shown that the cation causes a polarisation of the CH bonds and thus influences the proton shifts of the anion, both directly by its electric field along the bonds (the direct effect) and indirectly via its effect on the π‐electron distribution (the indirect effect). The indirect effect is inferred from 13C NMR chemical shift data. By subtracting the temperature dependent contribution of the indirect effect from the experimental 1H data, the direct effect is visualised. It appears that information on ion paris obtained by 1H and 13C NMR on the one hand and optical spectroscopy on the other hand is complementary. Apparently, aggregation of ion pairs does not seriously affect the chemical shift data.
13C‐NMR‐Spektren von Cyclopropenen und Benzocyclopropenen
Authors: Albert Karl‐Heinz , Dürr Heinz
Published: May 2005

Für Methyl‐, Halogen‐, Ester‐ und Phenylsubstituierte Cyclopropene und für Cyclopropenon und Diphenyl‐cyclopropenon werden aus den 13C‐chemischen Verschiebungen die Substituentenparameter bestimmt. Beiden Cyclopropenonen interessierte insbesonders der Einfluß der Carbonylgruppe auf die δ‐Werte und Ladungsdichten. Die Spektren von Di‐ und Tetraphenylsubstituierten Benzocyclopropendicarbonsäure‐Derivaten und des 1H‐Cyclopropa[a]naphthalin‐1,1 ‐dimethyl‐esters wurden in Hinsicht auf die Wechselwir‐kung zwischen Cyclopropenring und anelliertem Benzolring untersucht. Die J‐Werte erweisen sich dabei alsbessere Indikatoren für Strukturänderungen als die δ‐Werte, aus denen die Substituentenparameter bestimmt werden. α‐Effekte von Substituenten lassen sich mit den Hammett'schen σ1‐Werten korrelieren.
13C‐NMR‐Spektren isomerer Diazaphenanthrene
Authors: Könnecke Andreas , Lippmann Eberhard , Mlochowski Jacek , Sliwa Wanda
Published: May 2005

Die 13C‐chemischen Verschiebungen von elf isomeren Diazaphenanthrenen (1.5‐− 1.10‐, 2.7‐, 4.5‐− 4.7‐, und 5.6‐DAP) wurden bestimmt und iterativ durch Vergleiche mit geeigneten Modellverbindungen zugeordnet. Die erhaltenen Daten (132 Punkte) dienten zur Überprüfung der Beziehung zwischen 13C‐chemischen Verschiebungen und HMO‐Ladungsdichten. Die beste Korrelation mit einer Standardabweichung S(E) = 4.8 ppm ergaben die auf Phenanthren bezogenen chemischen Verschiebungen tertiärer Kohlenstoffatome. Die unterschiedlichen Steigungsfaktoren der Korrelationen für tertiäre und quartäre Kohlenstoffresonanzen (275–300 vs 540–550 ppm/Elektron) können auf verschiedene ΔE‐Werte für beide Typen von Kohlenstoffatomen zurückgeführt werden.
13C NMR chemical shifts of some highly‐branched acyclic compounds
Authors: Schwarz Richard M. , Rabjohn Norman
Published: May 2005

A study has been made of the 13C chemical shifts of a number of acyclic alkanes, alkenes, nitriles and ketones which contain quaternary carbon atoms. Similar data have also been obtained for the series of compounds involved in the synthesis of triisopropylacetic acid. Substituent effects and steric factors in these highly substituted compounds are discussed in relation to the chemical shifts.
Spectroscopic studies on olefins. VII–propene and 3‐methylbutene‐1; proton NMR coupling constants as a function of solvent and temperature in relation to molecular geometry
Authors: Rummens Frans H. A. , Simon Christian , Coupry Claude , Lumbroso‐Bader Nicole
Published: May 2005

The proton spectra of the compounds propene (1) and 3‐methylbutene‐1 (2) have been measured in various solvents and, as neat liquids, at variable temperature. The effects of solvent and temperature on 1 are found to be small, but not negligible. The effect of temperature on the coupling constants of 2 are more pronounced, which is explained in terms of an anti‐gauche equilibrium. To obtain a consistent ΔE° value from each temperature dependent coupling constant it is necessary to correct for the non‐conformational temperature effects (obtained from 1) as well as to correct for changes in the geometry of the entire molecule, which are concurrent with a conformational transition. Such geometry changes have been calculated by a consistent force field technique, which, when coupled with INDO‐MO calculated dependencies of coupling constants on valence (and torsional) angles, provided the changes in coupling constants. The observed temperature dependence of the coupling constants of the H2CCH— moiety of 2 could be satisfactorily explained in this fashion. The difference in energy between the anti and gauche forms of 2 were determined as ΔE° = 127 ± 14 cal mol−1.
Interproton coupling constant variations in 3‐membered ring heterocycles. Separation of lone pair and inductive effects
Authors: Crist Delanson R. , Borsetti Arnold P. , Jordan Guy J. , Hammer Charles F.
Published: May 2005

In order to separate inductive and lone pair effects on geminal and vicinal coupling constants in a stereochemically well‐defined system, the 1H NMR spectra of phenylcyclopropane (1), N‐methyl‐2‐phenylaziridine (2), styrene oxide (3) and 1,1‐dimethyl‐2‐phenylaziridinium fluorosulfonate (4) were compared. In D2O the heterocyclic ring protons of 4 were split into an ABX pattern which gave J(cis) = 8.5, J(trans) = 7.4 and J(gem) = −4.8 Hz (signs consistent with INDOR results). From the small solvent effects on J(vic) determined from 4‐d1, it was concluded that J(gem) is −5.0 ± 1.0 Hz in methylene chloride. The absolute values for the coupling constants for 1 and 4 provide a measure of the inductive effect of the ring hetero group on J. Values of J(gem) for 2 and 3 deviated from those predicted on the basis of the above inductive effect, suggesting lone pair contributions to J(gem) of c. +5.5 Hz per lone pair. With this estimate it was possible to predict accurately the J(gem) values for 2‐t‐butyloxaziridine and 1‐t‐butyldiaziridine. The values of J(cis) and J(trans) for 2 and 3 likewise suggested a contribution of −2.5 Hz to J(cis) and −2.7 Hz to J(trans) per lone pair. The present results suggest that the major factors causing positive J(gem) values in epoxides and aziridines are increased s character to the CH bonds and lone pair effects, while the so‐called electronegativity effect actually operates in the opposite direction to decrease J(gem). Also, the unusually low J(vic) values of epoxides relative to cyclopropanes are now seen to be due more to negative lone pair contributions than to the electron withdrawing ability of oxygen.