bluuebunny/crossref_metadata_2025 huggingface dataset:
(15N) acetamide in polar solvents: Hindered internal rotation and intermolecular interactions
Authors: Umemoto Kimiko , Ouchi Kenichi
Published: May 2005

The 1H spectrum of (15N)acetamide has been measured in dimethyl sulphoxide (DMSO), methyl propyl ketone (MPK), 1,3‐dioxane, 1,4‐dioxane, D2O, acetonitrile and pyridine‐d5 at various temperature intervals within the range of 278–343 K. From the temperature dependence of the NMR spectra of the amide protons, the free energy of activation, ΔG≠, for hindered rotation about the central CN bond was determined by means of total line shape analysis in the four solvents DMSO, MPK and the two dioxanes. Observed values of ΔG≠ (298 K) (72.7 in DMSO, 70.1 in MPK, 70.0 in 1,3‐dioxane and 70.1 kJ mol1 in 1,4‐dioxane) were not very sensitive to the choice of solvent or concentration. The concentration dependence of the internal chemical shift between the amide protons was studied in MPK, D2O, acetonitrile and pyridine‐d5. The free energy of activation and the internal chemical shift are discussed on the basis of solvent‐amide and amide–amide specific hydrogen bonding interactions, and in comparison to the results of molecular orbital calculations.
Substituent effects on 13C NMR. 2—chemical shifts in the saturated framework of secondary aliphatic derivatives
Authors: Ejchart Andrzej
Published: May 2005

13C chemical shifts obtained under uniform conditions for selected compounds containing secondary aliphatic fragments were employed in a linear regression analysis. Two‐parameter relationships describing the substituent effects in the saturated framework were calculated, and the usefulness of such calculations is discussed. Finally, coefficients for linear relationships in primary and secondary alkyl derivatives are compared.
Structure elucidation with lanthanide induced shifts. 7—development of a reliable method for structure evaluation and the application to organic nitriles
Authors: Raber Douglas J. , Janks Christopher M. , Johnston Milton D. , Raber Nancy K.
Published: May 2005

A useful and reliable procedure has been developed for the evaluation of the structures of organic nitriles using lanthanide shift reagents. The procedure is based on a statistical comparison of the experimental lanthanide induced shifts (LIS) with values which are predicted with the pseudocontact equation for a proposed structure. The experimental LIS are obtained by nonlinear regression analysis of the chemical shifts observed in the presence of varying amounts of the shift reagent, Eu(fod)3. The precise geometry for a proposed structure is obtained from molecular mechanics calculations. The LIS are then predicted with the pseudocontact equation using k=976.6 and a europium‐nitrogen bond length of 2.50 Å. (Detailed arguments are presented in support of these values.) The carbon‐nitrogen‐europium array is approximately linear, although small distortions from linearity are both expected and observed.
Paramagnetic products formed in the reactions of organometallic compounds. XII ESR study of oxido anion substituted diaryl ketyl radicals
Authors: Malik Ľ. , Staško A. , Mat'ašová E. , Tkáč A.
Published: May 2005

In the reactions of alkyl‐substituted‐benzenecarboxylic and ‐2‐hydroxybenzenecarboxylic acids (ArCOOH) with alkyl‐substituted phenyl Grignard reagents (RMgX) in the presence of nickel, ketyl radicals ArCO−R are formed. The para substituents (H, Me, Et, Isopr and t‐Bu) of R increase the non‐equivalence of its ortho protons (a change of a2H = 0.43 mT, a6H = 0.422 mT to 0.435 mT, 0.395mT respectively, on substituting t‐butyl for H at position 4). The oxido anion group originating from 2‐hydroxybenzenecarboxylic acid has a strong push effect and nearly doubles the unpaired spin density on the phenyl ring R.
The 15N NMR spectra of macrocyclic compounds containing the ferrocene unit
Authors: Hall C. Dennis , Bell Alan P. , Denney Dorthy Z.
Published: May 2005

The synthesis of a 15N enriched macrocycle containing the ferrocene unit is descibed, and the 15N NMR spectra of the macrocycle and those of its complexes with some metallic cations are reported.
Comparative 13C NMR study of the conformations of malic and thiomalic acids
Authors: Gil Victor M. S.
Published: May 2005

Vicinal and geminal 13CO2H1H coupling constants are reported for malic and thiomalic acids at various pH values and related, in a comparative manner, to the known conformational information obtained by 1H NMR.
Carbon‐13 NMR spectra of DDT, its analogues and related compounds
Authors: Freidlina R. Kh. , Dostovalova V. I. , Kuz'mina N. A. , Chukovskaya E. C.
Published: May 2005

Carbon‐13 NMR spectra of mono‐ and disubstituted aromatic compounds including DDT, its analogues, homologues, derivatives and certain model compounds have been studied. The Savitsky scheme of carbon chemical shifts in disubstituted benzenes is applicable to these compounds. The data obtained show that in mono‐ and disubstituted aromatic compounds containing two different substituents in the α‐ and β‐positions of the side chain, the substituted ring carbon atom shifts follow the additivity rule and can be calculated from substituent increments. Mutual effects of substituents in the ring and in the side chains are analysed. The chlorine atoms in α‐position to the phenyl ring give rise to an additive α‐effect of about 25 ppm, as in perchloroalkanes. The influence of a β‐chlorine atom in the side chain on the substituted carbon atom in the ring is, however, only 3 ppm as against the usual value of about 10 ppm for the β‐effect in alkyl chains. Moreover, the first β‐chlorine substituent has no noticeable influence on the substituted ring carbon chemical shift: the effect of 3 ppm is transferred to the para‐carbon atom almost without attenuation. The ring substituted carbon atom signal shifts caused by the γ‐effect of chlorine in the side chain are similar to those observed in aliphatic chains. The ortho‐chlorine substituents shift the side chain α‐carbon atom signal by 3.6‐5.2 ppm to high field compared to para‐chlorophenyl compounds. This is similar to the chlorine γ‐effect in aliphatic chains.
Carbon‐13 nuclear magnetic resonance of mono‐ and di‐chloro‐hexanes and mono‐ and di‐chloro‐heptanes. Assignment of configurations
Authors: Nouguier R. , Surzur J.‐M. , Virgili A.
Published: May 2005

Carbon‐13 NMR spectra of mono‐ and dichloro‐hexanes and mono‐ and dichloro‐heptanes are reported. Substituent effects for α, β and γ positions are presented. Differences between the 13C chemical shifts of diastereoisomers are observed in the cases of 2,4‐ and 2,5‐dicholohexanes and 2,4‐, 2,5‐ and 3,5‐dichloroheptanes.
15N NMR spectroscopy. 30—structure/shift relationships of oligopeptides and copolypeptides, including gramicidin S
Authors: Kricheldorf Hans R.
Published: May 2005

The 15N NMR spectra of various oligopeptide derivatives of the ZXYYOMe structure, where X and Y are variable amino acids and Z is the benzyloxycarbonyl group, were measured in several protic and aprotic solvents. The shift difference of the 15N of the YY and XY bond (neighbouring residue effect) is discussed with respect to the nature of X and Y with respect to the solvent. Oligopeptides of the ZXYYOH and n̊H3XYYOMe structures were compared with the Z‐pëptide esters to investigate the spectroscopic influence of the protecting groups. The methyl ester hydrochlorides of the 25 most common amino acids were measured in water and DMSO to elucidate the solvent dependence of the substituent effects. Moreover, the methyl ester hydrochlorides were compared with Z‐amino acids and N‐acetyl‐amino acid methyl esters in DMSO to establish whether the substituent effects depend on the nature of the amino acid derivatives. In this connection the assignments of the serine, threonine and glycine signals are discussed with respect to silk proteins. Furthermore, the assignments of the signals of copolypeptides by comparison with oligo‐ and homo‐polypeptides are discussed. Finally, it was demonstrated that intramolecular H bonds cause downfied shifts of 7–10 ppm of the acceptor amide groups.
Transmission of the substituent effects in 2‐substituted benzimidazoles studied by 1H and 13C nuclear magnetic resonance
Authors: Lopyrev V. A. , Larina L. I. , Vakul'skaya T. I. , Larin M. F. , Nefedova O. B. , Shibanova E. F. , Voronkov M. G.
Published: May 2005

The substituent influence on the 1H and 13C NMR chemical shifts in 2‐substituted benzimidazoles and their anions and cations has been investigated. The transmission of the electronic effects of substituents from C‐2 to C‐5 (6) is approximately 20% less effective than that in the opposite direction. The solvent influence on the chemical shifts of protons and transmission effects in the charged forms of 2‐substituted benzimidazoles has been studied.
NMR spectra of tricyclic compounds oriented in the nematic phase: The spectrum of phenazine
Authors: Khetrapal C. L.
Published: May 2005

The NMR spectrum of phenazine, the tricyclic diazine, oriented in a nematic phase is investigated. The ratios of the interproton distances are determined. They do not deviate significantly from the corresponding values in quinoxaline oriented in a thermotropic solvent.
14N NMR studies on some N‐sulphinylamines
Authors: Sicińska W. , Stefaniak L. , Witanowski M. , Webb G. A.
Published: May 2005

High precision 14N nuclear screening data are presented for some alkyl‐ and aryl‐N‐sulphinylamines. For the alkyl compounds the β effect is seen to produce a decrease in screening and the opposite influence from the γ effect is also observed. An exception to the general tendency for the β effect is noted for (CH3)3CNSO. CNDO/S parameterized nitrogen screening calculations show that for this molecule the distorted cis form, with all of the methyl carbons rotated out of the CNSO plane, is the most probable structure. A similar effect is observed upon substituting the bulky tert‐butyl group in the 2 position of the aryl compounds studied. Nitrogen screening calculations again indicate the presence of the distorted cis form.
Fourier transform NMR studies of organometallic compounds. II—synthesis and NMR spectroscopy of propenyl and isopropenyl derivatives of silicon and lead
Authors: Mitchell T. N. , Marsmann H. C.
Published: May 2005

Isomeric mixtures of compounds MenM(CHCHMe)4−n (M=Si, Pb; n=0−3) have been prepared and studied, as well as pure Me3M(CMeCH2) and mixtures containing propenyl isopropenyl residues bonded to silicon and lead. 1H, 13C, 29Si and 207Pb NMR data are presented; as previously observed for the corresponding tin compounds, the 29Si and 207Pb shifts for the Me3MC3H5 isomers can be used to calculate the shifts expected for the other isomers; while for lead the agreement is good, calculated and observed values for silicon diverge with decreasing n due, at least in part, to steric factors.
Signs of 1H, 19F spin—spin couplings in pentafluorobenzaldehyde
Authors: Schaefer Ted , Marat Kirk
Published: May 2005

The signs of the spin–spin coupling constants between the aldehydic proton and the fluorine nuclei in pentafluorobenzaldehyde are negative over four and six formal bonds and positive over five bonds. The opposite signs had been assumed in previous studies of this molecule. The correct signs are necessary for the determination of the conformational and substituent dependence of these coupling parameters.
Selenium‐77 nuclear magnetic resonance in mono‐ and disubstituted benzo[b]selenophenes
Authors: Baiwir Marcel , Llabrès Gabriel , Christiaens Léon , Piette Jean‐Louis
Published: May 2005

The 77Se chemical shifts of 79 mono‐ or disubstituted benzo[b]selenophenes are reported. The results in the 2‐ and 3‐substituted derivatives closely parallel those previously obtained in the corresponding selenophenes. The measured parameters also correlate well with those measured in benzo[b]tellurophenes. The 125Te and 77Se chalcogen nuclei appear to be much more sensitive to substituent effects than the more classical nuclei. The effects of Cr(acac)3, Eu(dpm)3 and concentration on the 77Se NMR spectra are briefly discussed.
1H and 13C NMR studies of two monosubstituted [2.2]paracyclophanes
Authors: Solladié‐Cavallo Arlette , Hibert Marcel
Published: May 2005

250 MHz 1H NMR of two monosubstituted [2.2]paracyclophanes shows that whether the substituent is an electron releasing group, OMe, or a withdrawing group, CO2Me, the transannular effect is deshielding. 62.86 MHz 13C NMR shows that among the six transannular effects, only one has a sign which changes with the nature of the substituent (–4.6 ppm for OMe but +3.3 ppm for CO2Me).
A 13C NMR study of pyridine in the presence of aqueous solutions of carbohydrates
Authors: Hall Laurance D. , Yalpani Mansur
Published: May 2005

Spin‐lattice relaxation rates of the 13C responses of pyridine were measured in the presence of aqueous sucrose and sodium alginate solutions and calcium alginate gels. In each case the results indicated a reduction in the overall tumbling rate of pyridine compared with that in aqueous media due to molecular association with the carbohydrate. Although anisotropic motion about the C‐4:N axis of pyridine was apparent in the sucrose solutions no consistent trends were observed for the alginate samples.
Interbenzylic 19F,19F spin‐spin coupling constants in bis(fluoromethyl) arenes
Authors: Ernst Ludger , Pulmann Sabine
Published: May 2005

Five‐ to eleven‐bond F,F spin coupling is observed in bis(fluoromethyl)arenes. According to INDO MO calculations, these couplings are transmitted mainly via the aromatic π‐system. The low preference of 1,4‐(CH2F)2‐benzene for the conformation in which the CF bonds are perpendicular to the aromatic ring is
shown by the strong increase of7J(FF) upon double ortho‐substitution.
1H NMR utilization of through‐space effects. II—conformation of dienic ketones
Authors: Rouillard Michel , Geribaldi Serge , Azzaro Marcel
Published: May 2005

The configurational and conformational assignments of the carbonyl group in the Z‐ and E‐1‐(3‐substituted‐5,5‐dimethyl‐2‐cyclohexen‐1‐ylidene)‐2‐butanones are carried out using only the through‐space effects of the carbonyl group. It is demonstrated that, regardless of the Z‐ or E‐configuration or the nature of the substituent in position 3, the conformation of the carbonyl group is always s‐cis.
1H NMR study of partially oriented 1‐phenylpropyne
Authors: Khetrapal C. L. , Highet R.
Published: May 2005

The proton magnetic resonance spectrum of partially oriented 1‐phenylpropyne has been studied and the values of the chemical shifts, the direct and the indirect coupling constants determined from the analysis of the spectrum. The ratios of the interproton distances have been derived. No significant deviations have been observed between the relative proton positions on the aromatic ring in 1‐phenylpropyne and those expected for the regular hexagonal geometry of the benzene ring. The results are insensitive to the mode of internal rotation of the methyl group about the CC bond.
Carbon‐13 and aluminium‐27 nuclear spin relaxation in triethylaluminum
Authors: Vestin U. , Kowalewski J. , Henriksson U.
Published: May 2005

Carbon‐13 spin–lattice relaxation times and nuclear Overhauser enhancement factors are reported for triethylaluminium in toluene‐d8 solution in the temperature interval 208–318 K. Aluminium‐27 linewidths are reported for the same solution in the temperature range 212–334 K. The effective correlation times at different positions in the molecule are determined and used for qualitative discussion of internal motions.
NQR investigations of 35Cl in crystalline 2,5‐dichloro‐4‐nitroaniline
Authors: Ramanamurti D. V. , Srihari D. , Venkatacharyulu P. , Premaswarup D.
Published: May 2005

Two NQR lines were observed for 35Cl in 2,5‐dichloro‐4‐nitroaniline at room temperature, using a self‐quenched super‐regenerative spectrometer. Analysis of the Zeeman effect on the two lines using a cylindrical single crystal reveals that the crystal belongs to the monoclinic system. The principal field gradient Z axes enclose an angle of 35° and 28° in the cases of the low and high frequency resonance lines, respectively. The b axis is parallel to 81°, 280°. The unit cell contains either two or a multiple of two molecules. The molecules in the crystal can be arranged into two sets, with the molecular planes in each set being parallel among each other. The angle subtended between the two planes is 159° and each of the planes is inclined to the b axis at an angle of 79.5°. There is an in‐plane bending of the two CCl bonds by 5.5°. The ionic, single bond and double bond characters of the CCl bonds for both chlorines are almost equal, and are in the ratio 24:73:3.
13C NMR spectra of some 4‐substituted protoadamantanes
Authors: Morgan S. E. , Rackham D. M.
Published: May 2005

The 13C NMR spectra of some mono‐ and geminal disubstituted protoadamantanes have been assigned with the aid of shift reagents.
19F and 1H NMR of aldimines of fluoroamino acids with pyridoxal‐5′‐phosphate
Authors: Beguin Claude , Hamman Sylvain
Published: May 2005

1H and 19F NMR spectra were obtained for six Schiff bases (aldimines) formed by pyridoxal‐5′‐phosphate (PLP) with four fluorinated or their two parent non‐fluorinated α‐amino acids (phenylalanine and α‐aminobutyric acid). pKA Values were derived from 1H and 19F titration curves. The imine nitrogen of the aldimines is very basic (∼13) and sensitive to the electron withdrawing effect of fluorine. The pyridine nitrogen is less basic in the aldimines (∼7) than in PLP (8.12) and is less sensitive to the electron withdrawing effect of the fluorine than is the imine nitrogen. The phosphate group has a pK in the same range (∼6) and the chemical shifts of some nuclei are sensitive to both pK values. Protonation of the aldimine causes the 1H signal to shift downfield at the methyl protons of the pyridine ring and at the aldehydic proton of the aldimine for the high pK value (except for the aldimines prepared from the β‐fluorophenylalanine), but upfield at the aromatic proton and at the aldehydic proton of the aldimine for the low pK. Protonation of the aldimine causes the 19F signal of an aryl fluorine to shift downfield but gives an upfield shift at a β‐fluorine. These data are related to the highly conjugated electronic structure of the Schiff bases.
Carbon‐13 nuclear magnetic resonance spectra of juvenile hormone III, some of its derivatives, and of analogous compounds
Authors: Kuhnz W. , Rembold H.
Published: May 2005

The 13C NMR spectra of methyl farnesoate and related compounds, including juvenile hormone III, are presented, as well as those of analogous compounds derived from methyl geranate. Correlations between the homologous derivatives are discussed in terms of substituent influences.
Compounds with bridgehead nitrogen. 40—Stereochemistry of perhydronaphthaleno[3,4‐e]pyrido[1,2c]‐[1,3]oxazines
Authors: Crabb Trevor A. , Mitchell Jacqueline S. , Turner Christopher H.
Published: May 2005

Seven of the possible diastereoisomeric perhydronaphthaleno[3,4‐e]pyrido[1,2‐c][1,3]oxazines have been synthesized and the configurations and preferred conformations of these assigned on the basis of IR and 1H NMR spectroscopy and the application of conformational principles.
High resolution NMR spectroscopy of heteroaromatic cations. II—pyrylium, thiapyrylium and seleninium cations
Authors: Sándor P. , Radics L.
Published: May 2005

High resolution 1H, proton coupled 13C and broad‐band decoupled 13C{1H} spectra have been recorded for pyrylium, thiapyrylium and seleninium tetrafluoroborates in CD3CN. Analysis of these spectra has provided accurate values and relative signs of all 1H,1H and 13C,1H coupling constants, as well as the magnitudes of all one‐ and three‐bond 13C,13C couplings observable in naturally occurring doubly‐labelled isotopomers. For the seleninium cation, the magnitudes and relative signs of all 77Se,1H and 77Se,13C coupling constants were also obtained. The chemical shifts and coupling data are compared, on a qualitative basis, with existing theoretical predictions.
NMR study of the complexation of boric acid with catechol (1,2‐dihydroxybenzene)
Authors: Pasdeloup Maurice , Brisson Colette
Published: May 2005

The boric acid–catechol system in aqueous solutions has been studied by means of 11B, 1H and 13C NMR over wide ranges of concentration and pH. 11B spectra show a striking difference between the complexation possibilities of dilute and more concentrated solutions of boric acid. Both the 1:1 and 1:2 complexes can be simultaneously observed by 13C NMR.
On the structure of dithizone
Authors: Rashidi‐Ranjbar Parviz , Yavari Issa
Published: May 2005

The 13C NMR spectrum of dithizone, unlike that of its oxygen analogue, shows only five different types of carbon atom. The 13C chemical shift of the CS group in dithizone is only 7 ppm to lower field of that of the CO moiety in its analogous compound. The results can be rationalized by consideration of tautomeric equilibria which lead to C2v time‐averaged symmetry.
15N,1H coupling constants in pyridines and pyrimidines An application of the INEPT pulse sequence
Authors: Städeli W. , Bigler P. , Von Philipsborn W.
Published: May 2005

Application of a modified INEPT pulse sequence to obtain fully proton‐coupled and selectively decoupled 15N NMR spectra of pyridines and pyrimidines with natural isotope abundance is demonstrated. The spectra are analysed for 2J, 3J and 4J(NH) coupling constants.
Carbon‐13 spectral analysis, tautomeric structures and conformations of four two‐ring methylene‐bridged phloroglucinol derivatives
Authors: Äyräs Pertti , Lötjönen Simo , Widén Carl‐Johan
Published: May 2005

The 13C NMR spectra of phloropyron BB, desaspidin BB, albaspidin BB and margaspidin BB were recorded and the structures of the compounds investigated with the aid of chemical shifts and CH coupling constants. The filicinic acid ring of the first three compounds appeared to have a monoketonic structure with the carbonyl group in position 2 (acyl group in position 3). The pyronone ring of phloropyron BB also has a monoketonic structure, with the carbonyl function adjacent to the ring oxygen. The two rings of the first three compounds attain a conformation where a stabilizing hydrogen bond(s) is (are) formed between the two rings, as shown by the observed CH couplings to some of the hydroxyl protons. The spectrum of margaspidin BB, whichconsists of two aromatic acyl phloroglucinol rings, indicates less inter‐ring hydrogen bonding interactions.
The anisotropic effect of 4‐substituents on the 1H NMR chemical shift of H‐5 in phenanthrenes
Authors: Letcher R. M.
Published: May 2005

Chloro‐, methoxy‐ and methyl‐substituents in the 4‐position of phenanthrenes exert a profound and diagnostic influence on the 1H chemicalshift of H‐5, and from 13C measurements it is considered to be dueto an anisotropic effect.
Carbon‐13 NMR spectra of polybromoalkanes and polychlorobromoalkanes. Structural increments of halogens in polyhalogenated groups
Authors: Dostovalova V. I. , Velichko F. K. , Vasil'eva T. T. , Kruglova N. V. , Freidlina R. Kh.
Published: May 2005

The 13C NMR spectra of 48 polychlorobromoalkanes have been studied. Unlike the 13C signals of chlorine‐containing groups (38–105 ppm), those of bromine‐containing fragments, with the exception of CBr2 (60–70 ppm), appear in a rather narrow range (25–50 ppm) and are shifted to higher field in relation to similar chlorine‐containing groups. The spin–spin coupling constants in similar bromine‐ and chlorine‐containing groups practically coinciEN. Calculation of the chemical shifts for the polyhaloalkanes under study according to the additivity scheme, as previously observed for polychloroalkanes, renders values which are in considerable discord with experimental values (up to –32 ppm for CBr3). These discrepancies may be compensated for by corrections for the binary interaction of halogen atoms by grouping the halogen‐containing fragments according to the geminal, vicinal, 1,3‐, 1,3,5‐ and 1,2,3‐arrangement of halogen atoms, and by introducing an increment for the position of the halogen at the secondary atom. It is established that as compared to 1‐monohaloalkanes: (a) in the case of the geminal arrangement of halogen atoms the α‐ and γ‐effects diminish (Δ α from –3.2 to –8 ppm; Δγ = 2.6 ppm), while the β‐effect increases slightly (from 0 to 1.2 ppm); (b) in the case of a vicinal arrangement both the α‐ and β‐effects diminish (by about –3.5 ppm) and the γ‐effect remains constant, as if the vicinal system of the halogens was topologically insulated; (c) for the 1,3‐ and 1,3,5‐arrangement of halogens their mutual influence is weak (about –0.5 ppm for each halogen atom in the α‐ and γ‐positions); (d) the 1,2,3 system (serial arrangement of halogen atoms) is the sum of two vicinal fragments and hardly deviates from the additivity scheme; (e) the arrangement of a halogen at the secondary C atom enhances the α‐effect (Δα = 2.8 and 1.0 for methyl and methylene, respectively, in the case of Cl, and 3.5 and 3.7 ppm in the case of Br); the variation of the β‐effect has a different sign in relation to CH3 and CH2 groups (+1.2 and –1.7 for Cl, and +2.5 and –1.0 for Br). More distant effects of halogens (δ and ϵ) were not considered. The determined increments (Δα, Δβ and Δγ) for the α‐, β‐ and γ‐effects of chlorine and bromine atoms allow the prediction of the 13C chemical shifts in polyhaloalkanes with an accuracy up to ±1.5 ppm. Some deviations of up to ±5 ppm may be connected with the influence of a three particle interaction of halogen atoms, which was taken into account only in the case of a geminal arrangement of halogen atoms.
Conformational equilibrium in 8‐methyl‐cis‐2‐thiahydrindane and 8‐methyl‐cis‐2‐oxahydrindane by 13C NMR spectroscopy
Authors: Willer Rodney L.
Published: May 2005

The preferred conformation of 8‐methyl‐cis‐thiahydrindane has been both estimated by 13C NMR chemical shifts and determined by low temperature 13C NMR spectroscopy to be the conformer with the methyl group equatorial with respect to the cyclohexane ring. This result is in disagreement with the interpretation of the temperature dependence of the CD spectra of (+) and (−) 8‐methyl‐cis‐2‐thiahydrindane, whereby the conformation with the methyl group axial with respect to the cyclohexane ring was claimed to be the preferred conformation. The preferred conformation of the related oxygen heterocycle, 8‐methyl‐cis‐2‐oxahydrindane, has been estimated by 13C NMR chemical shifts to be the conformer with the methyl group axial with respect to the cyclohexane ring. Possible reasons for these observations are discussed.
Enriched 13C NMR of a metallated α‐sulphinyl ester; temperature effect
Authors: Solladié‐Cavallo Arlette , Mioskowski Charles
Published: May 2005

Lithium and magnesium enolates of an α‐sulphinyl ester 83% 13C enriched at C‐1 and C‐2 are studied by 13C NMR at different temperatures. It is shown that two metaliated species are present in the case of lithium which exchange at −60°C, ΔG≠ −60° = 37.8 KJ mol−1 (9.05 Kcal mol−1) and that there is no rapid exchange between the non‐metallated ester and the metallated species (on the NMR time scale). In the case of magnesium, two or three metallated species are formed, according to the temperature which do not exchange up to 0 °C.
13C NMR studies of reduced porphyrin compounds. Aromatic delocalization pathways
Authors: Harel Yaacov , Manassen Joost
Published: May 2005

13C NMR spectra of ms‐tetraphenylchlorins, new aminoalkyl‐ and hydroxy‐pyrroline substituted ms‐tetra‐phenylchlorins, and ms‐tetraphenylisobacteriochlorins are presented and discussed. Significant changes in the chemical shifts of the α‐pyrrole, α‐pyrroline and meso skeletal carbons are found in chlorins and isobacteriochlorins in comparison to porphyrins. In contrast, the chemical shifts of the β‐pyrrole carbons are almost unaffected by the structural modifications in chlorin and isobacteriochlorin. The chemical shifts of the α‐pyrrole carbons in the various chlorins and isobacteriochlorins are strongly affected by the substitutents of the pyrroline ring, or by the introduction of an additional pyrroline ring in isobacteriochlorins. The results show that most of the electron density is concentrated in the unreduced part of the molecule, i.e. in the pyrrole rings and, especially, on the α‐pyrrole carbons and is transferred or removed through the aromatic pathway by substituents on the pyrroline ring. These observations are supporting evidence that the α‐pyrrole, α‐pyrroline and meso‐carbons are in the aromatic pathway and favour the proposal of a 16 atom dianion as the preferred delocalization pathway in chlorins and isobacteriochlorins.
The assignment of signals in the nitrogen NMR spectra of polycyclic diazines
Authors: Witanowski M. , Stefaniak L. , Webb G. A.
Published: May 2005

15N Nitrogen screening data are reported for some polycyclic azines and compared with previous results where available. INDO/S parameterized screening calculations for cinnoline and quinazoline help to decide between alternative nitrogen assignments. Nitrogen solvent shifts of several ppm are reported for all of the molecules studied.
Carbon‐13 nuclear magnetic resonance spectra of veratrine components
Authors: de Marcano Deanna , Méndez Bernardo , Parada Henry , Rojas Aníbal
Published: May 2005

The 13C NMR spectra were determined and signals assigned to the various carbons of veratridine and cevadine.
High field nuclear magnetic resonance spectra of hydroxyl protons of aldoses and ketoses
Authors: Gillet Brigitte , Nicole Daniel , Delpuech Jean‐Jacques , Gross Bernard
Published: May 2005

The hydroxyl protons of 23 monosaccharides in their pyranoid from (α or β) are examined by proton NMR at 250 MHz in DMSO‐d6 solutions. Intramolecular hydrogen bonding in sugar anions seems to be the major factor in accounting for the lack of parallelism between the pK values and the chemical shifts of the anomeric protons. Another important factor is the possibility of steric hindrance to the solvation of the acidic hydroxyls by the basic DMSO solvent molecules. Equatorial hydroxyls have, as a general rule, lower field chemical shifts (with some exceptions) and larger vicinal HOCH coupling constants, 3J, than axial hydroxyls. Moreover, equatorial hydroxyls are sensitive to the equatorial or axial position of their neighbours, in sharp contrast with axial hydroxyls. Long‐range 4J couplings are observed whenever a zig‐zag arrangement but a necessary condition is a simultaneous axial position of the OH and CH bonds in the above fragment. In this case, the combined use of vicinal (Karplus‐type equation) and long‐range coupling constants allows the description of the stereochemistry of the OH bond in a semiquantitative fashion.
Structure determination from the spin–lattice relaxation behaviour of quaternary carbons. Effects of deuterium substitution
Authors: Norton Raymond S.
Published: May 2005

The use of quaternary carbon relaxation data, including the effects of deuteration thereon, to obtain information about chemical structures is considered. It is shown that a simple qualitative analysis of the effects of deuteration is subject to a number of potential errors. Structural inferences should be based only on a rigorous quantitative analysis of the data. The effects of deuterium substitution on the relaxation behaviour of benzamide in solution have been measured. The data are accounted for satisfactorily by treating the molecule as an axially symmetric ellipsoid. Furthermore, it is found that deuteration has no significant effect on the rotational diffusion of benzamide in solution.
Application of 1H NMREu(fod)3shifted spectra for the determination of the enantiomeric composition and absolute configuration of secondary alcohols, using (−)‐ω‐camphanic esters
Authors: Jurczak Janusz , Konował Andrzej , Krawczyk Zbigniew , Ejchart Andrzej
Published: May 2005

The diastereomeric differences (Δδ) were measured for a series of 11 (−)‐ω‐camphanic esters of secondary alcohols of known absolute configuration, using 1H NMR spectroscopy with Eu(fod)3 as shift reagent. This method is convenient and useful for the measurement of enantiomeric compositions, whereas additional assumptions must be applied in determining the absolute configuration related to the signs of the diastereomeric differences.
13C,13C coupling constants from a mixture of isotopomers (13C) of substituted aromatic compounds; 1‐nitronaphthalenes
Authors: Hansen Poul Erik , Albrand Jean‐Pierre
Published: May 2005

13C Homonuclear decoupling experiments led to the assignment of the carbon‐carbon coupling constants of 13C‐enriched 1‐nitronaphthalene obtained by nitration of [1‐13C]naphthalene. The effects of substituents on coupling constants can be explained on the basis of the electronegativity of the first atom of the substituent, and the observed substituent effects are shown to be parallel to previous data for oxygen containing substituents.
1H NMR structural study of 2‐phenylthiazolidine
Authors: Térol A. , Subra G. , Fernandez J. P. , Robbe Y. , Chapat J. P. , Granger R.
Published: May 2005

Deuteration of 2‐phenylthiazolidine, and its complexation with the shift reagent tris(1,1,1,2,2,3,3‐heptafluoro‐7,7‐dimethyl‐4,6‐octanedionato)europium, have been used to study the signals and conformation of the heterocyclic protons and to interpret the 1H NMR spectrum of this 2‐substituted thiazolidine.
15N NMR spectroscopy 31—preliminary study on the insulin‐a chain (bunte salt form)
Authors: Hull William E. , Büllesbach Erika , Wieneke Hans‐Joachim , Zahn Helmut , Kricheldorf Hans R.
Published: May 2005

The Bunte salt derivative was prepared from bovine insulin‐A isolated from natural sources, and was purified by chromatography. Natural abundance 40.55 MHz 15N NMR spectra were measured in water and dimethyl sulphoxide. The latter solvent gave the best resolution, and 20 of the 22 possible amide nitrogen signals were detected. Several model oligopeptides were also measured and their usefulness for assignments is discussed.
Stereochemical study of hexahydro[1,3]thiazolo[3,2‐a]pyridines by 1H and 13C NMR
Authors: Barbry Didier , Ricart Guy , Couturier Daniel
Published: May 2005

Configurations and preferred conformations of a number of hexahydro[1,3]thiazolo[3,2‐a]pyridines have been assigned on the basis of their 1H and 13C NMR spectra. The conformational preferences of these compounds have been interpreted in terms of the minimization of dipolar type interactions, arising from 1,3 arrangements of the heteroatoms, which are increased by the electron donor induction effect of the alkyl groups. The stereochemistry of the salts of these bases is very different from that of the free compounds. For the gem‐disubstituted compound, an explanation in terms of the ‘gem‐dimethyl effect’ and a slight deformation at the nitrogen atom is proposed.
13C NMR spectra of cassane diterpenoids. The stereochemistry of the caesalpins
Authors: Connolly J. D. , Orsini Fulvia , Pelizzoni Francesca , Ricca Giuliana
Published: May 2005

Assignments of the 13C NMR resonances for some cassane diterpenoids have been made. The data have proved to be a useful tool for the stereochemical examination of the caesalpins.
Sterically hindered aromatic compounds. X—molecular distortions and asymmetry in a symmetrically substituted azobenzene
Authors: Barclay L. Ross C. , Dust Julian M. , Brownstein S. , Gabe E. J.
Published: May 2005

No significant steric effects are observed in the proton and carbon resonance spectra of 2,2′,4,4′,6,6′‐hexa‐t‐butylazobenzene, a very distorted molecule in the solid state.
Nitrogen‐15 nuclear magnetic resonance spectra of ketenimines
Authors: Eberl Karl , Roberts John D.
Published: May 2005

Nitrogen‐15 NMR spectra of 11 ketenimines have been taken both at the natural‐abundance level of 15N and with the aid of 15N‐labeling. The nitrogen chemical shifts are substantially different from those of neutral imines and are upfield, more like those of protonated imines. The results are in accord with significant delocalization of the nitrogen lone‐pair. Furthermore, there is a rough parallelism between the 13C shifts of the terminal carbons and the 15N shifts.
Selective population transfer in 15N and 13C NMR: Signs of 15NH and 15N13C coupling constants in secondary amide and iminium salts
Authors: Martineau H. , Trierweiler M. , Martin M. L.
Published: May 2005

The selective population transfer method has been applied to the study of a secondary amide and of the corresponding iminium salt. Important signal‐to‐noise enhancements were accessible in both fully coupled and proton decoupled 15N and 13C spectra. Moreover, the resolving power of the method was exploited for the accurate determination of long range 15N1H coupling constants. Experiments in which the selective inversion of transitions pertaining to the 15N satellite spectrum of multiplets which themselves constitute the 13C satellite spectrum of the main proton resonances could be carried out. The influence of a change from the amide to the iminium structure on the magnitudes and the signs of various 15N1H and 15N13C coupling constants is discussed.
NMR studies of actinomycins varying at the proline sites
Authors: Mauger A. B. , Thomas W. A.
Published: May 2005

The proton NMR spectra of 14 actinomycins and the 13C NMR data for four of these compounds were compared with those of actinomycin D. These compounds differ from actinmycin D by the replacement of one or both proline residues by sarcosine, azetidine‐2‐carboxylic acid, 4‐ketoproline, or cis or trans isomers of 4‐hydroxy‐, 4‐chloro‐ or 4‐methylproline. In those (aniso) compounds in which one proline residue is replaced, the possibility of isomerism was considered, since replacement could be located in either the α‐ or β‐peptide. Except for the sarcosine case, for which both isomers have been isolated, the aniso‐actinomycins gave spectra in which the presence of a second isomer was undetectable. Attempts to utilize the NMR data to determine which peptide contained proline, and which its congener, produced the tentative conclusion that in these compounds there is a biosynthetic preference for replacement of the β‐peptide proline residue. In comparing conformationally dependent NMR parameters for the various actinomycins, the most obvious variations appeared in the proline congener α‐proton splittings. Some of these (for cis isomers of 4‐chloroproline and 4‐methylproline) reflected different pyrrolidine ring geometries to that of proline, while others (for the corresponding trans isomers) did not. Only minor differences were apparent in the conformations of other regions of the peptide moieties.
Deuterium nuclear magnetic resonance spectroscopy. II—distribution of deuterium in some labelled nitrogen heterocyclic compounds
Authors: Al‐Rawi Jasim M. A. , Behnam George Q. , Taha Nihad I.
Published: May 2005

Pyridine, methylpyridines, quinoline and isoquinoline have been labelled with deuterium using pre‐reduced platinum dioxide (PtO2·2H2O) and heavy water. Their 2H chemical shifts from monodeuteriated TMS have been assigned. The extent of the labelling has been determined directly by 2H NMR spectroscopy.
1H and 13C NMR study of tri‐L‐serine in aqueous solution
Authors: Pogliani L. , Ziessow D.
Published: May 2005

270 MHz1H and 22.6 MHz13C NMR spectra of the tripeptide (L‐Ser)3 dissolved in D2O have been measured and completely analysed as a function of pD in the region from 1.1 to 10. The pK(NH2)=7.0 is distinctly lower than common values for N‐terminal residues. The chemical shifts for the peptide seryl residue change little with pD, with the H‐β1 and H‐β2 resonances being differently affected by the ionization of the COOH and NH2 groups. The 13C‐α chemical shift in the peptide seryl residue exhibits a sequence effect which is considerably larger than expected on the basis of recently reported mean shifts. Rotational isomerism about the C‐αC‐β bond is studied for the three different Ser residues on the basis of vicinal coupling constants 3J(H‐α, H‐β), and it is found that the population pb (‐OH gauche to ‐CO‐, and trans to ‐NH‐) in the N‐ and p‐Ser residues is notably larger than pb in Ser and Acetyl‐Ser. In. C‐Ser, In. C‐Ser, pb is comparable to pb in Ser, but is twice as large as pb in AcSer.
Dependence of the γ carbon‐13 shielding effect on the dihedral angle
Authors: Lambert Joseph B. , Vagenas Adelia R.
Published: May 2005

The γ effects on 13C shielding have been examined for a series of rigid molecules containing the substituents CH3, OH, NH2, F, Cl, Br or I. Plots of the γ effect vs the CC‐αC‐βX dihedral angle are well scattered if the plots do not distinguish modes of substitution. For the series in which the resonating carbon is CH2, however, fairly linear correlations are observed for XCH3, OH, NH2, Cl and Br. It is concluded that within a structurally defined and substitutionally homogeneous series, there is a reasonably linear stereochemical dependence. Although substitution at C‐α does not seriously alter the linear relationship, hybridization of the intermediate carbons may be important. The slopes of the plots for the γ effect vs dihedral angle are remarkably similar. Neither a strictly steric (van der Waals) nor a strictly polar source can be the cause of the linear relationship, since our series of substituents ranges widely with respect to both size and electronegativity. The only two factors that are constant within the series are the removal of the hydrogen atom (CCCH to CCCX) and the addition of the bonding and nonbonding orbitals on X that were not present on H.
Natural abundance proton‐coupled 15N NMR spectra of pyridines observed from proton polarization transfer experiments
Authors: Jakobsen Hans J. , Yang P.‐I. , Brey Wallace S.
Published: May 2005

Natural abundance proton‐coupled 15N NMR spectra have been observed for pyridine and a series of mono‐ and disubstituted pyridines using polarization transfer achieved by the selective population transfer method. The magnitudes and signs of the 15N1H spin‐spin coupling constants between the ring‐nitrogen and ring‐protons are determined from complete iterative spectral analysis and/or selective population transfer experiments. Substituent effects on the 15N1H coupling constants are discussed and compared with those for 13C1H couplings in substituted benzenes.
Carbon‐13 NMR spectra of some labdane diterpenoids
Authors: Patra Amarendra , Mitra Alok K. , Biswas Swapna , Gupta Chitra Das , Chatterjee Tapan K. , Basu K. , Barua A. K.
Published: May 2005

Carbon‐13 signal assignments of the labdane diterpenoids phlogantholide‐A, its diacetate and isophlogantholide‐A are reported. The assignments of the 13C NMR signals of 14‐deoxyandrographolide and its diacetate, made earlier, have now been confirmed by lanthanide shift studies on the former and also by 13C spectral studies on anhydroandrographolide diacetate and 14‐deoxy‐11,12‐didehydroandrographolide diacetate.
Spectral analysis of the high‐resolution proton‐coupled carbon‐13 NMR spectra of 1,3,2‐dithiarsolanes
Authors: Aksnes D. W. , Holak T. A.
Published: May 2005

The high‐resolution proton‐coupled 13C NMR spectra of 2‐chloro‐ and 2‐phenyl‐4‐methyl‐1,3,2‐dithiarsolane and 2‐chloro‐ and 2‐phenyl‐1,3,2‐dithiarsolane have been obtained and completely analysed. The spectral analysis has provided all the 13C chemical shifts and 13C1H coupling constants, including their relative signs. The results of this work are adequately interpreted in terms of two rapidly equilibrating half‐chair conformers with the 4‐methyl pseudo‐axial or pseudo‐equatorial. The cis isomers appear to be conformationally biased towards the form with the 4‐methyl pseudo‐equatorial. The two one‐bond 13C1H coupling constants of the methylene group are distinctly different. For both the cis and trans isomers, the largest one‐bond coupling always involves the methylene proton situated syn to the substituent at arsenic. The observed variation in the geminal and vicinal 13C1H coupling constants are discussed in terms of a stereospecific inductive effect of the sulphur hetero‐atoms and conformational factors.
NMR studies of the chalcogen analogues of benzofuran. IV—Proton, carbon‐13 and selenium‐77 magnetic resonance in nitrobenzo[b]selenophenes
Authors: Baiwir Marcel , Llabrès Gabriel , Christiaens Léon , Piette Jean‐Louis
Published: May 2005

The 1H, 13C and 77Se chemical shifts have been measured for mononitrobenzo[b]selenophenes. For the homocyclic nuclei, the observed 1H‐ and 13C‐values calculated from the empirical increments of nitrobenzene. Anomalous effects are observed in the 2‐ and 3‐substituted derivatives and the nature of the SeNO2 interactions in the former is discussed. 77Se chemical shifts of the 4‐, 5‐ and 7‐nitro derivatives are approximately correlated with the CNDO calculated electron densities; they also compare well with those of selenoanisoles and other phenyl alkyl selenides. The chemical shifts are also compared with the corresponding values in other heterocycles containing a selenophene moiety.
High resolution 1H NMR spectra of 2,2′‐biquinoline
Authors: Drake J. A. G. , Jones D. W.
Published: May 2005

From analysis and refinement by the LAOCOON III program of the 220 MHz 1H spectrum of 2,2′‐biquinoline, recorded as a saturated solution in carbon disulphide, most derived chemical shifts and coupling constants are close to corresponding values in quinoline. However, H‐3 is at 1.5 ppm lower field in 2,2′‐biquinoline than in quinoline and the ortho‐coupling 3J(34) in the heterocyclic ring is 0.5 Hz larger in 2,2′‐biquinoline than in quinoline; fairly free rotation about the 2,2′ bond is inferred.
Carbon‐13 NMR of polycyclic aromatic compounds. 1—Methoxybenz[a]anthracene‐7, 12‐diones
Authors: Wilbur David , Manning Wayne B. , Hilton Bruce D. , Muschik Gary M.
Published: May 2005

Benz[a]anthracene‐7, 12‐dione, eight monomethoxybenz[a]anthracene‐7, 12‐diones and two dimethoxybenz[a]anthracene‐7, 12‐diones were analyzed by 13C and 1H NMR. All 13C and 1H resonances have been assigned. Substituent effects on the 13C chemical shifts are discussed.
Signs of proximate 31P, 19F and 19F, 19F spin–spin coupling constants in 2‐trifluoromethylphenyldifluorophosphine
Authors: Schaefer Ted , Marat Kirk , Lemire Alberta , Janzen Alexander F.
Published: May 2005

In 2‐trifluoromethylphenyldifluorophosphine the proximate couplings 4J(19F31P) and 5J(19F19F) are + 68.3 and + 8.3 Hz, respectively. 1J(13C31P) is −57.0 Hz, 2J(13C‐1, 10F) is + 9.9 Hz and 2J(13C‐6, 13C‐6, 31P) is + 10.1 Hz. The trifluoromethyl substituent induces substantial changes in some coupling constants, particularly those between the 31P and ring 13C nuclei.
Studies in tertiary amine oxides. Part V—carbon‐13 nuclear magnetic resonance spectra of some N‐aryl tertiary amines, the corresponding N‐oxides and the meisenheimer rearrangement products
Authors: Khuthier Abdul‐Hussain , Al‐Rawi Jasim M. A. , Al‐Kazzaz Abdul K. , Al‐Iraqi Mohammed A.
Published: May 2005

The carbon‐13 NMR spectra of some N‐(2‐ or 4‐nitrophenyl) tertiary amines and their corresponding N‐oxides have been analysed. These N‐oxides undergo thermal rearrangement to O‐arylhydroxylamines, for which the 13C NMR spectral assignments were also carried out. The N‐oxidation effect on the aromatic and aliphatic fragments is calculated.
A 15N nuclear magnetic resonance study of the base‐catalyzed NH2 exchange reactions of acetamide and thioacetamide
Authors: Nee Michael , Chun Yu , Squillacote Michael E. , Roberts John D.
Published: May 2005

The base‐catalyzed NH2 exchange reactions of acetamide and thioacetamide were studied by 15N nuclear magnetic resonance spectroscopy by the use of line‐shape analysis. The 15N NMR spectra of these primary amides at intermediate exchange rates were broad doublets, which indicated that the two amide protons were exchanging at different rates. The line‐shape analysis indicated that the ratio of exchange rates was 6±1 for acetamide and 3±1 for thioacetamide.
13C NMR spectra of benzodiazepinones: Application to isomeric structure determination
Authors: Bernardini A. , Viallefont Ph. , Essassi E. M. , Zniber R.
Published: May 2005

A 13C NMR study of a number of substituted 1,5‐benzodiazepin‐2‐ones has been carried out, and shows that this technique is one of the rare spectroscopic methods which allows an unambiguous identification of the number and nature of the isomers formed in the condensation of a β‐ketoester with a substituted O‐phenylenediamine.