bluuebunny/crossref_metadata_2025 huggingface dataset:
An EPR study of the thermal decomposition of molten 2,4,6‐trinitrotoluene and its isotopic analogs
Authors: Swanson Jon T. , Davis Larry P. , Dorey R. Cameron , Carper W. Robert
Published: May 2005

Electron paramagnetic resonance spectroscopy has been used to probe the decomposition pathway of neat molten 2,4,6‐trinitrotoluene (TNT). The analogs of TNT labelled in the 2‐, 2,6‐, 4‐ and 2,4,6‐positions with 15N, and labelled in the α‐, 3,5‐ and α,3,5‐position with 2H have been studied, and their spectra recorded at 240°C. The results indicate that the earliest observable radical produces a spectrum resulting from coupling with a para‐N (aN = 10.8G), five equivalent hydrogens (aH = 2.7G) and two benzylic hydrogens (aH = 10.7G).
Natural abundance 15N chemical shifts in substituted benzamides and thiobenzamides
Authors: Brownlee R. T. C. , Sadek M.
Published: May 2005

15N Substituent chemical shifts (measured at natural abundantc at 0.4 M concentration) and calculated (ab initio, STO‐3G) electron densities at the nitrogen and oxygen (or sulphur) are reported for series of para and meta‐substituted benzamides and thiobenzamides with NMe2, NH2, OMe, NHCOMe, F, Cl, Br, I, Me, H, COMe, COOMe, CF3, CN, NO2, CONH2 and CSNH2 substituents. The 15N shift are very sensitive to the substituent effects. The dual substituent parameter method shows excellent correlations of 15N shifts against substituent field and resonance effects, with the sensitivity in the thiobenzamides being double that in the benzamides. In contrast, calculated π‐electron densities at the nitrogen show the same sensitivity to substituents in both series. The 15N shifts correlate well with the calculated π‐electron densities at the nitrogen; however, estimates of the shielding based on local electron densities (described in Pople's independent electron model) cannot account for the increased sensitivity to the substituent effects observed for 15N chemical shifts of thiobenzamides. It is suggested that non‐local shielding from sulphur and oxygen are responsible for the chemical shift trends.
Microcomputer‐based 13C NMR spectral simulation of substituted alkanes
Authors: Hearmon R. Angus
Published: May 2005

The empirical prediction of 13C NMR chemical shifts using the Lindeman‐Adams rules and substituent chemical shift parameters is a useful aid for the chemist in the interpretation of spectra. The program Alkanes, written in Basic for a desk‐top microcomputer, automates the chemical shift estimation.
Investigation of prototropic equilibria by carbon‐13 relaxation time analysis
Authors: Elst L. Vander , Van Haverbeke Y. , Maquestiau A. , Muller R. N.
Published: May 2005

Quaternary 13C dipole–dipole spin–lattice relaxation times are used to analyse prototropic equilibria of 2‐acetylbenzimidazole (1) and 4‐azabenzimidazole in DMSO‐d6 solutions. For the first compound, fast exchange between the two chelated structures prevails for 13C relaxation times, whereas proton and 13C chemical shifts characterize a slow exchange. For 4‐azabenzimidazole, 13C and 1H spectra do not exhibit absorptions from structures in slow exchange. Analysis of the T1 values of carbons 8 and 9 before and after isotopic exchange of the labile amino hydrogen clearly show that the major component of the equilibrium is the 3H structure.
13C NMR studies of polyaminocarboxylate complexes of Tl(III)
Authors: Anderegg G. , Popov K. , Pregosin P. S.
Published: May 2005

The 13C NMR characteristics of the polyaminocarboxylate ligands EDTA [(HO2CCH2)2NCH2CH2N(CH2CO2H)2],DTPA (HO2CCH2)2NCH2CH2N(CH2CO2H)CH2CH2N(CH2CO2H)2 and NTA [N(CH2CO2H)3] and their Tl(III) complexes are reported. The pH dependence of the 13C shifts of the ligands is helpful in understanding the 13C coordination chemical shifts, Δδ, but not the thallium‐carbon coupling constants J(205TI, 13C), which vary markedly for no apparent reason. The anion Tl(DTPA‐5H)2‐ contains three non‐equivalent coordinated carboxyl functions and a suggestion is made to account for this lower symmetry.
Rotational dynamics of molecules containing phenyl groups. A 13C spin‐lattice relaxation study
Authors: Dais Photis
Published: May 2005

13C nuclear magnetic resonance spin‐lattice relaxation times (T1) have been used to probe the motional behavior of diphenyl compounds of the type PhXPh (X = heteroatom or group of atoms). Analysis of the relaxation data by employing Woessnier's formalism has permitted an investigation of the influence of the bridge on the rotation of the phenyl groups and the calculation of potential barriers to phenyl rotation in solution, which otherwise are inaccessible.
Multinuclear NMR study of variously substituted sulphonamides and sulphinamides
Authors: Ruostesuo P. , Häkkinen A.‐M. , Mattila T.
Published: May 2005

13C, 15N and 17O NMR chemical shifts, and also 1J(CH) and 1J(NH) values, have been determined for variously substituted sulphonamides and some sulphinamides, either neat or in acetone or dimethyl sulphoxide solution.

The effect of benzene ring substituents on the chemical shifts of nitrogen and oxygen nuclei is slight, but N‐substitution changes the shielding of both nuclei. Generally, an N‐methyl substituent shields an amide nitrogen and an N,N‐dimethyl substituent gives further slight shielding. On the other hand, an N‐phenyl substituent deshields the nitrogen strongly, but the deshielding effect of an N,N‐diphenyl substituent is markedly smaller. The sulphonyl oxygens are deshielded relative to the sulphinyl oxygens, and N‐methyl and N,N‐dimethyl substituents shield the oxygen nucleus. The effect of N‐phenyl and N,N‐diphenyl substituents on the shielding of the oxygen atoms of the sulphonyl group is slight.

The direct 1J(CH) coupling constants are similar, but they are characteristic of different type of sulphur amides. The 1J(NH) values are of the same order of magnitude for sulphonamides and sulphinamides, but are clearly smaller for N‐unsubstituted amides than for N‐substituted compounds.
NMR studies of intramolecular proton exchange in alkylated naphthazarins
Authors: Elöve Gülnur A. , Schauble J. Herman
Published: May 2005

Three groups of alkyl‐substituted naphthazarins were studied by 1H and 13C NMR in chloroform‐d at ambient temperature. Preliminary 1H NMR studies were carried out on selected members of each group at low temperatures (down to –120 °C) in dichloromethane‐d2 solution. Monoalkylnaphthazarins were found to exist predominantly as the 2‐alkyl tautomers (I) and the dimethylalkyl species as the 2,3‐dimethyl‐6‐alkyl tautomers (I). However, both symmetrically and unsymmetrically substituted 2,6‐ and 2,7‐dialkylnaphthazarins exhibited averaged chemical shifts and coupling constants indicating rapid proton exchange between the two minimum energy 1,4‐dione tautomers (I and II). 13C NMR shifts were utilized to calculate tautomer populations of the unsymmetrical 2,6‐ and 2,7‐(methyl,alkyl)naphthazarins.
Two‐dimensional NMR analysis of the phytohormone gibberellin A3
Authors: Preiss A. , Adam G. , Šaman D. , Buděšinsky M.
Published: May 2005

The complete analysis of the 1H NMR spectra of the phytohormone gibberellin A3 and its 3,13‐diacetyl derivative has been performed. ASIS and 2D J‐resolved spectroscopy were used to disentangle the complex spin systems, which were further analysed by 1H‐1H homocorrelated spectroscopy and spin decoupling. 2D 1H‐13C shift correlated spectra not only supported the identification of individual protons but also allowed the clarification of some controversial 13C assignments.
Assignment of carbonyl groups and sequence analysis in peptides by inverse correlation using long‐range couplings
Authors: Bermel Wolfgang , Griesinger Christian , Kessler Horst , Wagner Klaus
Published: May 2005

Inverse heteronuclear shift correlation via long‐range coupling to the carbonyl carbons of the cyclic hexapeptide cyclo(‐Phe11‐Thr10‐Aia9‐Trp8‐Phe/‐D‐Pro6‐) allows the sequential assignment of the amino acids. This experiment has a higher sensitivity than the conventional COLOC sequence.
Carbon‐13 chemical shifts and carbon‐proton coupling constants in 4H‐ and 9aH‐quinolizine esters and some of their methyl derivatives
Authors: Kamieńska‐Trela Krystyna , Raynes W. T. , Taylor B. F.
Published: May 2005

The proton coupled and decoupled 13C NMR spectra of 4H‐quinolizine 1,2,3,4‐tetracarboxylate and its less stable tautomer 9aH‐quinolizine 1,2,3,4‐tetracarboxylate have been investigated. All 13C resonances have been assigned, and a number of the one‐, two‐ and three‐bond carbon‐proton coupling constants obtained for these compounds and some of their methyl derivatives. The principal conclusion from the data is that the nitrogen atom is positively charged as a result of extensive conjugation.
NMR spectra of the porphyrins. 30—Calibration and application of a ring current model for cobalt(III) meso‐tetraphenylporphyrin (CoTPP) complexes
Authors: Abraham Raymond J. , Medforth Craig J.
Published: May 2005

The geometry of metalloporphyrin‐ligand complexes [mono‐(1:1) and bis‐(1:2)] produced by cobalt(III) meso‐tetraphenylporphyrin (CoTPP) with amine ligands has been investigated using the diamagnetic ring current shifts of the porphyrin on the ligand nuclei.

The observed ring current shifts are corrected for complexation effects by the use of cobalt(III) dimethylglyoxime (DMG) complexes. Significant changes in ligand chemical shifts are observed on formation of a DMG complex, although saturated ligands only show changes at points close to the site of complexation.

Crystallographic data and corrected ring current shifts for pyridine and N1‐methylimidazole are used to parameterize a double‐dipole model of the CoTPP ring current. For 4‐methylpiperidine a geometry calculated from corrected ring current shifts is in reasonable agreement with that observed in the solid state. The geometry calculated for a cyclohexylamine CoTPP complex can be rationalized in terms of a minimization of steric interactions with the porphyrin.

Corrected 13C ring current shifts are still in poor agreement with calculated values, although there is a considerable improvement compared with uncorrected values.
Natural abundance 17O NMR spectra of coumarins, furocoumarins and related compounds
Authors: Duddeck Helmut , Rosenbaum Doris , Elgamal M. Hani A. , Shalaby Nagwa M. M.
Published: May 2005

The 54.2 MHz 17O NMR spectra of a series of naturally occurring coumarins and furocoumarins and those of a number of related model compounds are described. The 17O chemical shifts of the furocoumarins can be predicted by the evaluation of the data of substructures in model compounds. syn‐Periplanar γ‐ and long‐range interaction effects can be interpreted in terms of steric and electronic effects.
A 13C NMR study of hindered rotation in N1,N1‐penta‐ and N1, N1‐hexa‐methylene‐N2‐substituted‐phenylformamidines
Authors: Wawer Iwona
Published: May 2005

Rates of rotations about the C‐N1 partial double bond in a series of six N1,N1 penta‐ and six N1,N1‐hexa‐methylene‐N2‐substituted‐phenyformamidines were determined from 13C DNMR line shape analysis.

Electron accepting substituents at the phenyl ring increase the barrier to rotation, and electron donating substituents decrease the barrier, compared with the nonsubstituted compound. Linear relationships are shown to exist between ΔG≠ and the 13C chemical shifts of the functional carbon or the pKa of formamidines.
Carbon‐13 NMR spectra of some c‐6 methylated steroids
Authors: Iida Takashi , Tamura Toshitake , Matsumoto Taro
Published: May 2005

13C NMR signals were assigned for a series of C‐6 rnethylated steroids related to 5α‐cholestane, and the substituent effect of methyl groups at C‐6 on the shielding data is discussed.
13C, 17O and 1H NMR study of the protonation of acetone in water
Authors: Shen Lian‐fang , Du You‐Ru , Shao Qian‐fen , Mao Shi‐zhen
Published: May 2005

The protonation of acetone in water for a wide range of compositions of the binary mixture was studied by multinuclear NMR spectroscopy. Formation constants (K1 and K2) and 13C, 17O and 1H chemical shifts of the 1:1 and 1:2 complexes were evaluated. The correlation of the 1H chemical shift of uncombined water with its concentration, Δ
= A + B In [H2O]eq, recently derived for the trimethyl phosphate‐water system, was verified. A measure of the fraction of monomer species existing in the uncombined water at each composition was obtained. The results are discussed with respect to the structure of water.
High‐field proton NMR study of the liquid solution structure of monomeric bacteriochlorophyll a and chlorophyll a
Authors: Lötjönen S. , Michalski T. J. , Norris J. R. , Hynninen P. H.
Published: May 2005

The 500 MHz proton spectra of monomeric bacteriochlorophyll a and chlorophyll a were recorded and assigned. The proton chemical shifts and proton‐proton coupling constants were all determined except for the P‐5 to P‐15 phytyl side‐chain protons. The conformational structures of the reduced rings and associated side‐chains in these compounds were deduced from vicinal coupling constants. The reduced ring IV and the propionic ester side‐chain in bacteriochlorophyll a and chlorophyll a have identical conformations which, in addition, are very similar to those reported previously for methyl pheophorbide a and pheophytin a. The reduced ring IV of bacteriochlorophyll a, which is attached to the phytyl side‐chain, is more buckled than the other reduced ring (ring II).
Ring A conformation in steroids. 2—NMR study of C‐2 monomethyl‐ and dimethyl‐substituted 5α‐androstan‐3‐ones
Authors: Marat Kirk , Templeton John F. , Gupta R. K. , Kumar V. P. Sashi
Published: May 2005

Ring A proton shifts and couplings and 13C shifts of all carbons are given for 17β‐acetoxy‐2α‐methyl‐ and 17β‐methoxy‐2β‐methyl‐5α‐androstan‐3‐one and 2,2‐dimethyl‐17β‐methoxy‐5α‐androstan‐3‐one. It was concluded that the 2β‐methyl derivative exists with ring A in a regular chair conformation while the 2β‐methyl derivative exists with ring A in an inverted boat conformation with C‐2 and C‐5 at the bow/stern positions. The data for 2,2‐dimethyl‐17β‐methoxy‐5α‐androstan‐3‐one suggest an equilibrium of these two conformers.
NMR studies in the heterocyclic series XXX—Carbon‐13 NMR study of 5‐nitrofurfural derivatives
Authors: Mester B. , Claramunt R. M. , Elguero J.
Published: May 2005

Fifteen 5‐nitrofurfural imino derivatives with antitrypanosomiasic activity have been studied by 13C NMR spectroscopy. Chemical shifts have been assigned and 13C1H coupling constants have been measured.
13C, 31P and 1H NMR studies of chiral bis[(4R,6R)‐4,6‐dimethyl‐1, 3, 2‐dioxaphosphorinan‐2‐yloxy]alkane derivatives. Coupling between phosphorus atoms six bonds apart
Authors: Szalontai G. , Bakos J. , Tóth I. , Heil B.
Published: May 2005

13C, 1H and 31P NMR investigations were carried out to confirm the stereochemistry of novel bis[(4R,6R)‐4,6‐dimethyl‐1,3,2‐dioxaphosphorinan‐2‐yloxy]alkanes. The 13C NMR spectra exhibited second‐order features at room temperature. Substantial coupling was found between P atoms six bonds apart. The possibility of a through‐space contribution was tested. Spatially close P atoms and the strongly electronegative P substituents (oxygen atoms) are thought to be responsible for the enhanced P… P coupling.
1H and 13C nuclear magnetic resonance of phenyldibenzophosphole and derivatives: Complete assignment using two‐dimensional J‐resolved and shift correlation methods
Authors: Nelson John H. , Affandi Salina , Gray George A. , Alyea Elmer C.
Published: May 2005

Proton and 13C NMR parameters have been determined for phenyldibenzophosphole and its oxide, sulfide, selenide and W(CO)5 complex from high‐resolution one‐ and two‐dimensional (COSY, HETCOR and 2DJ) experiments at 4.7, 7.1 and 9.4 tesla. Assignments of chemical shifts and coupling constants have been made and verified by computer simulation of the proton spectra. The data are discussed in relation to the geometry and electron density at phosphorus and the diamagnetic anisotropy of the W(CO)5 group.
A one‐dimensional selective version of the INADEQUATE experiment for determining carbon—carbon connectivities. Analysis of multi‐pulse experiments by a vectorial representation
Authors: Canet D. , Brondeau J. , Boubel J. C. , Retournard A.
Published: May 2005

The simple pulse sequence (π/2)x‐τ‐(π/2)‐x(π/2)φ(Acq)ψ allows selective polarization transfer from a nucleus A (on resonance) towards any nucleus X, J coupled to A, provided that τ is properly varied around ½J with coaddition of the relevant FIDs. With an appropriate phase cycling, parent signals in a natural abundance 13C spectrum are eliminated. This consequently leads to the unambiguous determination of all carbons coupled to A. A universal vectorial representation aimed at multi‐pulse sequence analysis is proposed and applied to the present experiment.
13C NMR chemical shifts, in some N‐chloro‐2,6‐diarylpiperidin‐4‐ones
Authors: Ul Hasan Misbah , Arab M.
Published: May 2005

The 13C shifts in several N‐chloro‐2,6‐diarylpiperidin‐4‐ones have been measured and compared with previously reported sifts in the corresponding 2,6‐diarylpiperidones. The shifts of the α‐carbons in these compounds move downfield by 12–13 ppm, which can be attributed to the increased electronegativity of the nitrogen atoms. The changes in the chemical shifts of the β‐carbons are minimal. Surprisingly, the absorptions of the carbonyl carbons move upfield by as much as 4.0 ppm. The magnitude of the shift in the resonance of the carbonyl carbon indicates the possibility of a transannular interaction between the nitrogen and the carbonyl group, which has not previously been observed in these systems. A preferred conformation for the aryl group in these compounds is also proposed.
NMR study of substituent effects in 4‐substituted and 4,4′‐disubstituted diphenyl sulphides
Authors: Chandrasekaran R. , Perumal S. , Wilson D. A.
Published: May 2005

The proton and carbon NMR spectra of nine 4‐X‐diphenyl sulphides (series 1), seven 4‐X‐4′‐NO2‐diphenyl sulphides (series 2) and eight 4,4′‐X2‐diphenyl sulphides (series 3) have been obtained. Correlation of the 13C chemical shifts with the appropriate substituent chemical shifts (SCS) for monosubstituted benzenes (Lynch plots) show an enhancement of substituent effect at C‐1 (carbon para to the substituent) in series 1 and 2, but not in series 3. The carbons of the unsubstituted ring in series 1 also correlate with Cp‐SCS, with slopes of less than unity; correlation for C‐1′ has a negative slope. Dual substituent parameter (DSP) correlations of the 13C chemical shifts with σI/σoR are good to excellent for all the carbons of series 1 compounds, except those ortho to the substituent X. The carbons meta to the substituent X correlate well, but with negative values for ρI and ρR, although showing a scattered Lynch plot. Similar correlations are found with some carbon shifts in series 2, and with C‐1 shifts in series 3.

It is concluded that (a) reverse resonance effects are operative at the position meta to the variable substituent by virtue of the sulphur substituent ortho to that carbon; (b) there is transmission of inductive (field) and resonance effects from one aryl ring to the other, except when both rings carry substituents of the same electronic character (series 3); (c) there is some evidence for π‐polarization in the unsubstituted phenyl ring of series 1 compounds.
Study of the monomer‐dimer equilibrium of nitrosobenzene using multinuclear one‐ and two‐dimensional NMR techniques
Authors: Orrell Keith G. , Šik Vladimir , Stephenson David
Published: May 2005

The monomer‐dimer equilibrium of nitrosobenzene in CDCI3 solution was studied in the temperature range ‐50 to 30 °C using 13C, 15N and 17O NMR spectroscopy. Decreasing temperature favours the dimeric azodioxy species, and below ca 10 °C both cis and trans dimers were detected in addition to the monomer. The relative abundance of the trans dimer is low (⩽6%) at all temperatures and this is the first report of its existence in solution. The monomer and dimer species were characterized by their 13C and 15N shifts, and exchange between them was measured quantitatively by 13C 2D‐EXSY spectra. Exchange occurred exclusively between the cis‐dimer and monomer and between the trans‐dimer and monomer, activation energies, ΔG≠(298.15 K) being 65.8±0.1 and 70.0±0.3 kJ mol−1, respectively.
Carbon‐13 and phosphorus‐31 NMR spectroscopy of phenoxychlorocyclotriphosphazenes, N3P3Cl6‐n(OC6H5)n
Authors: Reuben Jacques
Published: May 2005

The 31P and 13C NMR spectra of all twelve phenoxychlorocyclotriphosphazenes of general formula N3P3Cl6‐n(OC6H5)n (n = 1‐6) were assigned in detail. With samples abundant in one homolog, but with a disparity between geometrical isomers, the signals due to the cis and trans isomers of N3P3Cl4(OC6H5)2 and N3P3Cl2(OC6H5)4 were also assigned. The 31P chemical shifts and coupling constants correlate linearly with the level of substitution, n. The 13C NMR spectra exhibit complex multiplets for the ipso‐ and ortho‐carbons. It is shown that each of these is the X part of one of the spin systems XAM2, XAA′M, XAA2′, XAB2 and XAA′B. The 13C chemical shifts of the ipso‐ and para‐carbons also exhibit correlations with n. The 13C‐31P coupling constants, both 2J(POC) and 3J(POCC), are larger for the PCl(OC6H5) than for the P(OC6H5)2 moieties.
13C NMR spectra of eudesmanolides. II. Eudesman‐12,8‐olides
Authors: Marco J. A. , Carda M.
Published: May 2005

The 13C NMR spectra of 20 natural and synthetic eudesmanolides, including the naturally occurring sesquiterpene factones 1‐deoxy‐8‐epiivangustin, yomogin, 1‐deoxyivangustin and isoalloalantolactone, and of nine related eudesmane derivatives have been measured and interpreted. Substitutent effects are briefly discussed.
13C NMR chemical shift substituent effects. 4–α‐monosubstituted acetones
Authors: Rittner Roberto , Vanin José A. , Wladislaw Blanka
Published: May 2005

13C NMR chemical shifts for some α‐heterosubstituted acetones were recorded. The carbonyl carbon shieldings are discussed in the light of the substituent electronic effects and were also empirically estimated by Tanaka et al.'s equation. An approximate linear relationship was observed between the 13C and 17O chemical shifts. A nonadditivity of substituent chemical shifts was observed for the α‐methylene carbon, and attributed to intramolecular interactions between the α‐heteroatom and the carbonyl group.
Configuration of cross‐conjugated caroten‐20‐als: 2D NMR study on four isomers of renierapurpurin‐20‐al
Authors: Englert Gerhard , Glinz Ernst , Liaaen‐Jensen Synnøve
Published: May 2005

The 400 MHz 1H NMR spectra of four cis isomers of synthetic renierapurpurin‐20‐al (χ,χ‐caroten‐20‐al) were completely assigned by application of two‐dimensional proton‐proton chemical shift correlated spectroscopy (2D COSY) with high digital resolution of ca 0.4 Hz per point by acquisition of only the olefinic part of the spectra. Connectivities to the methyl and aldehyde protons absorbing outside the measured range were also obtained owing to the folding of their cross‐peaks along the F1 axis. Nuclear Overhauser difference experiments and consideration of chemical shift changes were applied to derive unequivocally the 13‐cis (13E), 7,13‐di‐cis (7Z), 13,7′‐di‐cis (7′Z) and 13,9′‐di‐cis (9′Z) configuration of the isomers. The 1H‐detected one‐bond 1J(CH) and long‐range 2,3J(CH) multiple quantum coherence heterocorrelated 2D spectra of 1.2 mg of the main 13‐cis isomer were acquired and the 13C signals partly assigned. The structural consequences with respect to other cross‐conjugated caroten‐20‐als are discussed.
1H, 2H, 19F, 14N ENDOR and TRIPLE resonance investigations of substituted flavin radicals in their different protonation states
Authors: Weilbacher E. , Helle N. , Elsner M. , Kurreck H. , Müller F. , Allendoerfer R. D.
Published: May 2005

A variety of isotopically labelled and/or substituted flavins have been converted into their corresponding radical states. Cation and neutral radicals were generated chemically and anion radicals were obtained electrochemically. By performing ENDOR and TRIPLE resonance experiments, complete sets of hyperfine coupling constants including their signs were accessible. The hyperfine data allowed (a) identification of the radical state present, (b) information to be obtained about the preferred conformational arrangements of the substituents and (c) conclusions to be drawn about the influences of the substituents on the spin density distributions of the different radical states.
Heteronuclear directed site‐selective NOESY spectroscopy by polarization transfer or multiple quantum filtering
Authors: Volk A. , Mispelter J. , Dimicoli J. L. , Papamichael E. , Sakarellos C.
Published: May 2005

Two methods are examined which allow a NOESY experiment to be performed involving only a specific site of the molecule labelled by a heteronucleus. They involve the merging of a classical phase‐sensitive NOESY experiment with either an INEPT sequence, which transfers 1H magnetization to a coupled heteronucles, or a multiple quantum filtering sequence which allows the selection of only the 1H resonances which are coupled to the heteronucles. The two methods are first compared on two small molecules, non‐labelled alanine and [U‐13C]alanine, particularly with respect to the signal‐to‐noise ratio. An example of the application of these methods on a 25000 molecular weight protein system (elastase‐peptide complex) is also given. The limitations of the methods, in particular in terms of T2, are discussed.
A 13C study of hydroxymethyl derivatives of five‐membered ring heterocycles
Authors: Katritzky Alan R. , Law Kam Wah
Published: May 2005

The 13C spectra of the hydroxymethyl derivatives of pyrrole, furan, 5,5‐dimethylhydantoin, imidazole, thiophene, pyrazole, and phenol have been studied and assigned. The substituent parameters for the hydroxymethyl group in pyrrole, thiophene, furan, and imidazole were determined.
Complete 1H and 13C spectroscopic assignments for the antibiotic novobiocin and NOE evidence for multiple conformations
Authors: Pearce C. M. , Sanders Jeremy K. M.
Published: May 2005

The 1H and 13C NMR spectra of the antibiotic novobiocin have been fully assigned by a combination of homonuclear and heteronuclear two‐dimensional techniques. One‐dimensional NOE difference spectra provide evidence for multiple conformations of the carbohydrate moiety with respect to the coumarin group. Mobile parts of the molecule gave positive NOEs whereas all other parts gave negative NOEs.
Proton and carbon‐13 NMR study ofN‐(β‐benzoylethyl)‐β‐alanine ethyl esters and their hydrochlorides
Authors: Avrsa Maria Chiara , Ferlazzo Alida , Giannetto Placido
Published: May 2005

1H and13C NMR chemical shifts and coupling constants ofN‐(β‐benzoylethyl)‐β‐alanine ethyl esters and their hydrochlorides are reported; the assignments of the13C resonances are based on chemical shift arguments, analysis of the splittings and comparison with model compounds.
Stereochemical analysis and complete 1H/13C NMR chemical shift assignments of matrine. Application of NOE and two‐dimensional NMR techniques
Authors: Gonnella Nina C. , Chen Jen
Published: May 2005

The stereochemical and structural analysis of matrine was carried out using nuclear magnetic resonance spectroscopy. Several methods, including 13C1H two‐dimensional shift correlation spectroscopy, 1H1H two‐dimensional correlated spectroscopy and measurements of vicinal 1H1H coupling constants were used for chemical shift assignments and configurational analysis. Nuclear Overhauser effect difference spectroscopy was used to establish the sterochemistry. This investigation demonstrates the power of two‐dimensional NMR techniques and the nuclear Overhauser effect (NOE) in the structural determination of natural products.
13C NMR chemical shift trends and conformational changes in alkali metal cation complexes of a series of naphthalene crown ethers
Authors: Johnson Mark R. , Colburn Christopher A. , Ganion Susan J. , Son Byungki , Mosbo John A. , Sousa Lynn R.
Published: May 2005

13C NMR studies of alkali metal cation complexation by six related crown ethers are described. The crown ethers (and ions studied) were 2,3‐naphtho‐20‐crown‐6 (Na+, K+, Rb+, Cs+), 2,3‐naphtho‐17‐crown‐5 (Na+, K+, Rb+, Cs+), 2,3‐naphtho‐14‐crown‐4 (Na+, K+, Rb+, Cs+), 1,8‐naphtho‐21‐crown‐6 (Na+, K+, Rb+, Cs+), 1,8‐naphtho‐18‐crown‐5 (Na+, K+, Rb+, Cs+) and 1,5‐naphtho‐22‐crown‐6 (K+, Rb+, Cs+). For each crown ethercation combination, 13C NMR spectra were obtained for a number of different ion concentrations in CD3OD. Data were analysed by a non‐linear least‐squares treatment to give complexation constants and chemical shifts that would result at the limit of complete 1:1 complexation. Analyses of the limiting chemical shifts for a number of carbons indicate regular, cation‐dependent trends (for Cs+ through Na+). Deviations from these trends are interpreted as reflecting differences in conformations of crown ether–cation complexes. Conformational differences between cation complexes that occur near the point of naphthalene attachment cause deviations from the trend in the aromatic carbon chemical shifts, while conformational differences further from the naphthalene cause trend deviations only in the crown ether carbon chemical shifts.
Accurate exchange rate constants from valley‐to‐peak intensity ratios of a two‐site system with equal populations
Authors: Perrin Charles L.
Published: May 2005

The valley‐to‐peak ratio of a 1:1 doublet undergoing chemical exchange can be calculated from the line shape equation. Numerical analysis provides a table that permits the evaluation of the rate constant from that ratio. This method is exact, without the approximations of previous equations that suffer from systematic errors. Statistical analysis shows how the experimental error depends on the rate constant and how to weight rate constants of unequal reliability for least‐squares analysis. From the tabulated errors it is possible to recognize conditions to optimize the evaluation of rate constants, so that it is realistic to obtain them with a precision of ± 1–2%.
31P nuclear magnetic resonance spectroscopy of the phosphorylated tetrapeptide GlyGlyAspAla
Authors: Schlemmer Heinz , Sontheimer Gerhard M. , Kalbitzer Hans Robert
Published: May 2005

The model peptide glycylglycylaspartylalanine was phosphorylated in the NMR sample tube and characterized by 31P NMR spectroscopy. The pKa2 value of the acyl phosphate group in glycylglycyl(β‐aspartyl phosphate)alanine was determined to be 4.6 and the chemical shift was −6.45 ppm at low pH (1.5) and −1.27 ppm at high pH (8.0).
Deuterium isotope effects as a conformational probe in cyclic and acyclic ketones
Authors: Berger Stefan , Diehl Bernd W. K.
Published: May 2005

Cyclic ketones from cyclobutanone to cyclohexadecanone were labelled with deuterium in the α‐position. The deuterium isotope effect on the 13C NMR spectra was measured and in some cases was indicative of perturbation of conformational equilibrium. Similar effects were observed with acyclic ketones. The results were confirmed by temperature‐dependent measurements and molecular mechanics calculations.
Magnetic properties in terms of localized quantities. VIII—Azines and azoles
Authors: Schindler Michael
Published: May 2005

Second‐order magnetic properties, i.e. magnetic susceptibility and chemical shift tensors, of some five‐ and six‐ membered heterocycles containing nitrogen were calculated by means of the IGLO method. The molecules studied were the azoles pyrrole, pyrazole, imidazole, 1,2,3‐triazole, 1,2,4‐triazole, and 1H‐ and 2H‐tetrazole, together with the corresponding N‐methyl‐substituted compounds, the azines pyridazine, pyrimidine, pyrazine, s‐triazine, 1,2,3‐triazine, s‐tetrazine, pyridine and borazine.

Confirming previous investigations, good agreement was found between calculation and experiment. Only the calculated NMR shifts of nitrogen atoms that are involved in NN multiple bonds are too paramagnetic (deshielded). This effect (probably due to the neglect of electron correlation) is much less pronounced for the partial NN double bonds in aromatic rings than for genuine NN multiple bonds studied previously.
13C NMR investigations of phenol–triethylamine complexes: Ion pair–molecular complex tautomerism
Authors: Ilczyszyn Marek , Ratajczak Henryk , Skowronek Krzysztof
Published: May 2005

The tautomeric equilibria in phenol–triethylamine complexes have been quantitatively investigated. A method of calculation of thermodynamic parameters based on reproducing the temperature dependences of 13C chemical shifts is described. The results are in agreement with UV and IR predictions for similar complexes. The chemical shifts characterizing molecular forms of the complexes depend on the type of phenol derivative.
Configurations and conformations of some methyl‐substituted 2,4‐dioxabicyclo[3.3.1]nonanes
Authors: Mattinen Jorma , Pihlaja Kalevi , Czombos Jószef , Bartók Mihály
Published: May 2005

Three dimethyl‐ and one trimethyl‐2,4‐dioxabicyclo[3.3.1]nonanes were prepared and their configurations and conformations were determined by means of multinuclear high‐field NMR spectroscopy. Even at 400 MHz the proton spectra were so degenerate that several 2D experiments and, also, deuterium NMR had to be used to make the spectral analysis possible. 13C and 17O NMR spectra are also reported. The information obtained shows that two of the dimethyl derivatives are in boat–chair conformations with 3α9syn and 3α6α configurations, whereas the third dimethyl and the trimethyl derivative exist in chair–chair conformations with 3β9syn and 3β9syn9anti configurations.
Carbon‐13 NMR relaxation studies of gluconate and manganese—gluconate interactions
Authors: Coffin David B. , Carper W. Robert
Published: May 2005

The effect of temperature on the spin–lattice (R1) and spin–spin (R2) 13C relaxation rates of gluconate and manganese (II)–gluconate interactions was determined in D2O. An R2 vs T−1 minimum was observed for gluconate similar to that observed in solid‐liquid phase transitions. Nuclear Overhauser enhancement factors indicated predominately dipolar relaxation mechanisms for all atoms except the carbonyl carbon. Activation energies and chemical shifts indicated a molecular reorientation involving the carbonyl carbon which resulted in changes in solvation effects. Addition of manganese(II) to gluconate in D2O resulted in an observed minimum in the R1 vs T−1 plots for all carbon atoms except the carbonyl species. The activation energies further supported the concept of changes in solvent‐manganese‐gluconate interactions produced by variations in intramolecular structure.
1H and 13C NMR study of hindered rotation in N1,N1‐dimethyl‐N2‐substituted phenylacetamidines
Authors: Wawer Iwona
Published: May 2005

Barriers to rotation about the partial double CN1 bond were determined from line shape analysis of 1H and 13C dynamic NMR spectra of N1,N1‐dimethyl‐N2‐substituted phenylacetamidines with twelve different substituents on the phenyl ring. The values of ΔG are 51.2–58.7 kJ mol−1 and the correlation with Hammett's σ values indicates an important contribution from the substituent effects to the barrier height. The decrease of the rotational barrier of approximately 10 kJ mol−1 in acetamidines in comparison with the respective formamidines is probably mainly due to a steric interaction of the CCH3 group with aromatic protons; this leads to non‐planarity and a decrease of the conjugation of the aromatic ring with the acetamidine moiety.
Carbon‐13 to nitrogen‐14 coupling constants in some heterocyclic cations containing quaternary nitrogen atoms
Authors: Taylor Michael J. , Calvert David J. , Hobbis Catherine M.
Published: May 2005

Spin–spin coupling between 14N and 13C nuclei is observed in NMR spectra of some quaternary ammonium compounds, including a series of heterocyclic cations. 1J values are in the range 2.2–4.2 Hz. Instances of coupling through two and three bonds are also reported and these are correlated with 13C chemical shift data for the structures concerned.
Carbon‐13 NMR spectra of 1,6‐bis derivatives of hexa‐2,4‐diynes
Authors: Majumdar K. C. , De R. N. , Sen B. K. , Banerji A. , Mitra A. K.
Published: May 2005

13C NMR data for 1,6‐bis derivatives of hexa‐2,4‐diynes are reported. Introduction of a sulphone or sulphoxide moiety at C‐1, C‐6 in place of sulphide, ether or amino groups caused a 6–7 ppm upfield shift (β effect) for the C‐2, C‐5 carbons and a 3–4 ppm downfield shift (y effect) for the C‐3, C‐4 carbons.
Stereochemical factors determining the effects of glycosylation on the 13C chemical shifts in carbohydrates
Authors: Shashkov Alexander S. , Lipkind Grigory M. , Knirel Yuriy A. , Kochetkov Nikolay K.
Published: May 2005

Basic stereochemical factors have been revealed which affect the 13C chemical shifts in glycosides with a chiral cyclohexane‐type aglycone and in disaccharides with a pyranosidic aglycone. The effects of glycosylation depend on the configuration of the anomeric centre of the glycosylating sugar residue (glycone) and on the relative absolute configuration of the glycone and aglycone. When at least one of the carbons of the aglycone, adjacent to the glycosylated carbon, bears an equatorial proton, this dependence is well accounted for by a strengthening or weakening of the spatial interaction between the protons of the glycone and aglycone, caused by a change in the conformation around the glycosidic linkage. Regularities in the glycosylation effects for disaccharides are generalized for various modes of substitution and different general configurations of the pyranosidic aglycones. Simple rules have been formulated for the prediction of the magnitudes of the glycosylation effects which can be used for the determination of some unknown structural elements in glycosides and disaccharides, in particular the absolute configuration of one of the constituent sugars.
Compounds with bridgehead nitrogen. 57—NMR spectra and stereochemistry of protonated perhydrooxazolo [3,4‐a]pyridines, perhydropyrido[1,2‐c] [1,3] oxazine and perhydropyrido[1,2‐c] [1,3]oxazepine
Authors: Crabb Trevor A. , Trethewey Andrew N.
Published: May 2005

Protonation of perhydrooxazolo[3,4‐a]pyridine, perhydropyrido[1,2‐c][1,3]oxazine and perhydropyrido[1,2‐c][1,3]oxazepine by hydrogen chloride gas in diethyl ether gave mixtures of trans‐ and cis‐fused hydrochlorides containing 28, 75 and 79% of the trans‐fused salts, respectively, which compare with free base equilibria containing 68, 90 and 74% trans‐fused conformers. The cis‐fused salts from perhydrooxazolo[3,4‐a]pyridine existed in solution (CDCI3, 298 K) as an equilibrium containing 55% O‐inside cis‐ and 17% O‐outside cis‐fused conformers. Similar mixtures, but with smaller percentages of cis‐fused salts, were formed in D2ODCI.
Pseudohalogen chemistry. IX—Substituent constants (Z) for the isothiocyanato group in the estimation of the chemical shifts of vinyl protons inα,β‐unsaturated isothiocyanates
Authors: Guy Robert G.
Published: May 2005

Substituent constants for the isothiocyanato group (Z 0.92, Z 0.01 and Z −0.22) were derived by an additivity procedure, and shown to reproduce the chemical shifts of vinyl protons in a wide variety of α,β‐unsaturated isothiocyanates with an accuracy of ±0.30 ppm in 92% of the cases studied. Deviations are discussed in terms of the steric and field effects of the substituents involved.
Structural studies on some mesoionic compounds using nitrogen NMR
Authors: Jazwinski J. , Stefaniak L. , Webb G. A.
Published: May 2005

1H, 13C, 14N and 15N NMR data are reported for two 1,2,3,4‐oxatriazolium‐5‐thiolates and for two 1,2,3,4‐thiatriazolium‐5‐olates. It is demonstrated that nitrogen NMR is the most sensitive technique for determining the structures of these mesoionic compounds; of particular significance is the N‐2 chemical shift, which distinguishes between the presences of either oxygen or sulphur in position 1. Cyclic structures are confirmed for these compounds on the basis of the nitrogen chemical shifts.
13C1H shift correlation with full 1H1H decoupling. II—Further significant improvements in resolution and sensitivity
Authors: Reynolds William F. , McLean Stewart , Perpick‐Dumont Marion , Enríquez Raúl G.
Published: May 2005

In previous work a modified COLOC sequence combined with a selective BIRD pulse which allows one to obtain one‐bond 13C1H shift‐correlated spectra with full 1H1H decoupling and good (ca 15 Hz)f1 resolution, in addition to improved sensitivity over earlier sequences measured under the same conditions, was developed. In this paper it is demonstrated that a further modification of this sequence to allow the pair of 1H and 13C 180° pulses to traverse the entire fixed evolution period allows excellent (ca 7–8 Hz) f1 resolution plus a further increase in sensitivity (in the same time) of almost √2. Factors contributing to the sensitivity advantages relative to other sequences were examined. Whereas some artifacts are noted for tightly coupled CH2 groups, these may actually aid in the accurate determination of very small chemical shift differences. The precision of measurement of 1H chemical shifts is ca 1 Hz.
Relaxation of platinum‐195 in tetracyanoplatinate(II) and hexacyanoplatinate(IV) in aqueous solutions
Authors: Wasylishen Roderick E. , Britten James F.
Published: May 2005

The mechanism of 195Pt spin–lattice relaxation in aqueous solutions of Pt(CN)− and − has been elucidated from variable‐temperature T1 measurements at 4.70 and 8.48 T. For Pt(CN)− both the chemical shielding anisotropy and spin rotation mechanisms are important; for Pt(CN)− the spin rotation mechanism completely dominates. The value of Δσ obtained for Pt(CN)− is 2350 ppm, which is in excellent agreement with the value previously measured for the tetracyanoplatinate(II) ion in a variety of salts in the solid state.
Determination of the 18‐α/18‐β configuration of pentacyclic triterpenes. A multivariate data‐analytical approach
Authors: Grahn Hans , Masino Charles J. , Nordén Bo , Edlund Ulf
Published: May 2005

It is shown that by using a multivariate statistical approach the analysis of the 13C chemical shifts of variously substituted 18‐α/18‐β pentacyclic triterpenes can be significantly simplified. By examination of the components that result from a principal components data analysis, it is possible to separate configurational information from substituent induced changes. New structures can be predicted from the obtained model. The present approach minimizes the risk from incorrect assignments, or other errors, which are associated with large data tables.
13C NMR spectra of substituted carbazoles and azacarbazoles (β‐carbolines)
Authors: Erra‐Balsells Rosa
Published: May 2005

13C NMR spectra of a series of derivatives of carbazole and azacarbazole (norharmane or 9H‐Pyrido [3,4‐b]indole) are reported. The dependence of 1H and 13C shieldings on molecular geometry is discussed briefly.
1H and 13C NMR spectral studies of some biquinoline derivatives and a re‐investigation of the reaction of quinoline with sodium
Authors: Osborne Alan G. , Green Richard , Sadler Ian H. , Reed David
Published: May 2005

The 360 MHz 1H and 15 MHz 13C NMR spectra of 2, 2′‐biquinoline, 2,3′‐biquinoline and 6,6′‐dimethyl‐2,3′‐biquinoline are presented and assigned. The diamagnetic anisotropic effect of the neighbouring aromatic ring (Dc) and the electrostatic field effect of the nitrogen lone pair (DN) result in characteristic deshielding effects in the 1H NMR spectra of these compounds. The characteristic chemical shift differences (ΔH and Δc) between nuclei at the corresponding position but on different rings is proposed as an additional assignment aid for the 1H and 13C NMR spectra of unsymmetric biaryls and biheteroaryls. The reaction of quinoline and of 6‐methylquinoline with sodium gives the 2,3′‐biquinoline.
Investigation of hydrogen‐bonded compounds using high‐resolution NMR spectroscopy in solids. Part 3—1H chemical shifts in polycrystalline trihydrogen selenites
Authors: Rosenberger H. , Scheler G. , Moskvich Yu. N.
Published: May 2005

1H high‐resolution NMR spectra of polycrystalline alkali trihydrogen selenites were measured at 270 MHz using the combination of a multiple‐pulse sequence and magic angle sample spinning. Good resolution of the separate 1H NMR lines belonging to different hydrogen bonds in these crystals was obtained. Correlations between the measured average values of the chemical shift tensor and the parameters characterizing hydrogen bond [R(O…O) and R(H…O)] distances and the deuteron quadrupolar coupling constant e2qQ/h are presented. These correlations are found to be linear, with high correlation coefficients for the ordered protons. The possibilities of designating disordered protons on finding large deviations from the correlations for ordered protons are discussed.
DEPT‐related sequences for selective long‐range heteronuclear chemical shift correlation spectroscopy
Authors: Kövér Katalin E. , Batta Gy.
Published: May 2005

DEPT‐related sequences are proposed which suppress the generally unnecessary direct proton‐carbon correlations from the long‐range optimized heteronuclear chemical shift correlation spectra. One‐bond modulation of long‐range response intensities is removed through the use of a BIRD pulse train. It is demonstrated that these modified sequences are superior to the original 2D DEPT experiment for the detection of long‐range connectivities of protonated carbons.
14N NMR nuclear shielding and the electronic structure of dibenzo[1,3a,4,6a]tetrazapentalene
Authors: Witanowski M. , Sitkowski J. , Sicińska W. , Biernat S. , Webb G. A.
Published: May 2005

14N NMR data and semiempirical molecular orbital calculations are reported for dibenzo‐[1,3a,4,6a]tetrazapentalene (1). The 14N signals were assigned by means of the results of the molecular orbital calculations and measured relative signal widths. A comparison was made with results for some azolopyridines. A linear correlation was obtained between the nitrogen shieldings, expressed with respect to the bridging nitrogen atom, and the corresponding relative charge densities. Thus nitrogen nuclear shielding results provide a good estimation of electron charge distribution in these molecules. Compound 1 provides the first case in which the shielding of a pyridine‐type nitrogen atom is greater than that of the indolizine‐type nitrogen.
Natural abundance 17O NMR spectra of chromanones, chromones, flavanones and flavones
Authors: Duddeck Helmut , Jászberényi Joseph Csaba , Lévai A. , Timár Tibor , Elgamal M. Hani A.
Published: May 2005

17O NMR data for some chromanones, chromones, flavanones and flavones are discussed in terms of steric, mesomeric and inductive substituent interactions, intramolecular hydrogen bonding and conformational changes. It is shown that such effects can be used to rationalize 17O NMR data of compounds with larger and more complicated structures.
High‐field 2D NMR spectroscopy of amanitin isomers
Authors: Pehk T. , Haga M. , Vija H. , Lippmaa E.
Published: May 2005

The 1H, 13C and 15N NMR spectra of α−, β− and γ‐amanitins and amaninamide were recorded at 11.7 T and analysed by various two‐dimensional (2D) NMR spectroscopic techniques. All diastereotopic protons were assigned, and the side‐chain conformations and the conformation of the hydroxyproline residue were determined. The observed 15N chemical shifts are caused by non‐bonded interactions of the peptide nitrogens. 1H, 13C and 15N data are complementary to each other and show that the conformation of β‐amanitin is slightly different from that of the other isomers, in accordance with the lower toxicity. The NOESY and carbonyl 13C1H chemical shift diagrams confirm the closeness of the conformations of amanitins in DMSO solution to that of β‐amanitin in the crystalline state.
34S isotope effects on 31P chemical shifts in thiophosphate esters
Authors: Bjorholm Thomas , Larsson Flemming C. V.
Published: May 2005

The 34S isotope effect on 31P chemical shifts was measured for 15 different alkyl thiophosphates. For the doubly bonded S a linear relationship exists between the magnitude of the isotope effect and the 31P chemical shift. For the singly bonded S no such correlation was found.