bluuebunny/crossref_metadata_2025_split huggingface dataset:
1H and 13C chemical shifts and coupling constants of lupane. Application of two‐dimensional NMR techniques
Authors: Ammann Willi , Richarz René , Wirthlin Toni , Wendisch Detlef 
Published: May 2005

Abstract2D NMR techniques (J‐resolved 13C, 13C13C correlated, 1H13C correlated) were used to gather more chemical shift and coupling information on the pentacyclic triterpene, lupane. They confirm and complete 13C assignments made earlier, and corroborate the constitution and major configurational details of lupane. Lupane is a parent compound and spectral reference in the study of sedimental demethylated triterpenes.
Application of two‐dimensional NMR spectroscopy to the complete analysis of the 1H and 13C NMR spectra of d‐biotin in aqueous solution
Authors: Ikura Mitsuhiko , Hikichi Kunio 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of d‐biotin were observed at 400 and 100 MHz, respectively. Various types of two‐dimensional NMR spectroscopy were performed to assign the spectra. The previous assignment of 13C NMR spectrum of d‐biotin reported by Bradbury and Johnson was modified, and the dihedral angles between the CH bonds of the ring were determined. The populations of the conformers produced by internal rotation around the C‐2C‐δ bond were estimated.
Some CNDO/S parameterized calculations of intramolecular effects on nuclear shielding
Authors: Hamdi B. T. , Reynolds D. J. , Webb G. A. 
Published: May 2005

AbstractSome shielding calculations, using Pople's SOS model, are reported for B, C, N, F, P and Si as a function of changes in bond length and pyramidal bond angle. In all cases considered, the shielding is predicted to decrease as the bond length increases, which is in line with the available experimental data. The observed temperature variation of the nitrogen and phosphorus shieldings of NH3, PH3 and PF3 could be accounted for by a decrease in the pyramidal angle at higher temperatures. A similar angular variation for NF3 is predicted to cause a shielding variation, with temperature, in the same sense as that reported for NH3 and PH3, but opposite to that for PF3.
The 13C NMR spectra of homoisoflavonoids
Authors: Kirkiacharian B. S. , Gomis M. , Tongo H. G. , Mahuteau J. , Brion J. D. 
Published: May 2005

AbstractThe study of a set of 3‐benzylidene‐4‐chromanones, 3‐benzyl‐4‐chromanones, 3‐benzyl‐3‐hydroxy‐4‐chromanones and 3‐benzylchromones (homoisoflavonoids) by 13C NMR spectroscopy shows the influence of the structure of these molecules on the chemical shifts of the more characteristic carbon atoms at positions 2, 3 and 4.
15N and 13C NMR study of the effects of hydrogen bonding and protonation in linear schiff bases: Models for structural studies of rhodopsin and bacteriorhodopsin
Authors: Muccio D. D. , Copan W. G. , Abrahamson W. W. , Mateescu G. D. 
Published: May 2005

AbstractThe effects of protonation and hydrogen bonding in linear Schiff bases obtained from n‐butylamine with butyraldehyde, crotonaldehyde, sorbaldehyde and all‐trans‐retinal were studied by means of 15N and 13C NMR. The protonation‐induced chemical shifts (Δδ) are an order of magnitude larger for 15N than for 13C. For 15N, this effect was found to increase with the extent of conjugation, culminating in the retinylideneimine (Δδ = −146 ppm), which constitutes a model for the study of the structure of the Schiff base linkage in visual pigments and related systems. Theoretical calculations of protonation‐induced Δδ values based on MINDO/ 3 are in agreement with experimental results.
A study of C–35Cl coupling constants and 35Cl relaxation times through 13C relaxation in the rotating frame
Authors: Mlynárik Vladimír 
Published: May 2005

AbstractValues of one‐bond J(C35 Cl) and T1(35Cl) were determined for small chlorine‐containing molecules through 13C scalar relaxation in the rotating frame. A method is suggested for evaluating the contribution of scalar relaxation which eliminates experimental imperfections. The magnitude of J(C35Cl) seems to be influenced by the same factors as J(CF) values. The differences in 35Cl relaxation times are rationalized in terms of the molecular reorientation time.
A long‐lived molecular association between acetone and 2‐methoxy‐5‐aminopyridine
Authors: Ortiz F. S. , de Kowalewski D. G. , Contreras R. H. , Facelli J. C. 
Published: May 2005

AbstractStudies were carried out in order to determine the nature of a peculiar solvent effect observed between acetone and 2‐methoxy‐5‐aminopyridine. It is concluded that a molecular complex is formed due to specific interactions that take place between the solute and solvent. This molecular species is sufficiently long‐lived to produce two separate NMR spectra.
Carbon‐13 chemical shift assignment of some N substituted derivatives of (E)‐hydroxyazastilbenes
Authors: Łapucha Andrzej , Wyrzykiewicz Elżbieta 
Published: May 2005

AbstractCarbon‐13 NMR spectra of 24 new N‐carboxyalkyl‐ and N‐alkoxycarbonylalkylsubstituted derivatives of (E)‐4‐styrylpyridine and (E)‐4‐o(m‐ or p)hydroxystyrylpyridine bromides have been calculated and fully assigned. The Ai and AiK empirical parameters of the N‐carboxyalkyl, N‐alkoxycarbonylalkyl, N‐carboxyalkyl‐4‐vinylpyridyl and N‐alkoxycarbonylalkyl‐4‐vinylpyridyl groups were calculated for the prediction of the chemical shifts of substituted stytylpyridines.
Conformational preference of substituted naphthalenes. 2—proton–proton coupling constants of hydroxy derivatives of naphthalene
Authors: Salman Salman R. 
Published: May 2005

AbstractLong‐range proton–proton coupling constants between the hydroxy proton and ring protons were employed to deduce the conformational preferences of 1‐ and 2‐hydroxynaphthalene. 2,6‐Dibromo‐1,5‐dihydroxy‐naphthalene, 2‐acetyl‐1‐hydroxynaphthalene, 1,6‐dibromo‐2‐hydroxynaphthalene and 2‐hydroxy‐1‐naphthaldehyde were used as model compounds. Molecular orbital calculations at the CNDO/2 and INDO level were used to calculate the energy and the long‐range proton–proton coupling of different conformers of 1‐ and 2‐hydroxynaphthalene.
13C and 17O chemical shifts and conformational analysis of mono‐ and di‐methyl‐substituted thiane 1‐oxide and thiane 1,1‐dioxide
Authors: Barbarella Giovanna , Dembech Pasquale , Tugnoli Vitaliano 
Published: May 2005

AbstractThe 13C and 17O (natural abundance) chemical shifts of several mono‐ and di‐methyl ring‐substituted thiane 1‐oxides and thiane 1,1‐dioxides are reported. The cis and trans isomers of methyl‐substituted thiane 1‐oxide are readily identified by 13C and 17O NMR. In particular, the 17O NMR signals of axial SO groups are found several ppm upfield of those of the equatorial counterparts. The proportion of axial and equatorial conformers of thiane 1‐oxide in different solvents has been measured by low‐temperature 13C NMR. In THF the proportion of the axial conformer is higher than in CD2Cl2 whereas in CDCl3 or CHF2Cl the conformational preference is reversed and the equatorial conformer is slightly favoured.
13C NMR investigations of phenol–triethylamine complexes: Influence of hydrogen bond interaction on the electronic structure of the aliphatic chain
Authors: Ilczyszyn Marek , Latajka Zdzisław , Ratajczak Henryk 
Published: May 2005

AbstractThe influence of hydrogen bond formation on 13C chemical shifts at the α and β positions of triethylamine and tri‐n‐butylamine has been investigated by dipole moment measurements and CNDO/2 calculations. It has been shown that a hydrogen bridge dipole moment occurs during complexation. Moreover, the change observed in the C‐αC‐β bond dipole moment is proportional to the hydrogen bridge dipole moment, but is approximately 100 times smaller. This change has been related to differences between the 13C chemical shifts at the α and β positions of amines.
Conformational preferences of 2‐methoxy‐acetophenone
Authors: Schaefer T. , Peeling James , Wildman Timothy A. 
Published: May 2005

AbstractOn the basis of the presence or absence of long‐range spin–spin coupling constants between side–chain and ring nuclei in 2‐methoxyacetophenone, some literature ambiguities about the conformational preferences of the side‐chains in this compound can be resolved. The long‐range coupling between the methoxy protons and the ring proton ortho to the methoxy group, 5J(H, CH3)o, is (−)0.28 ± 0.02 Hz, as expected for a conformation in which the methoxy group lies in the benzene plane and cis to H‐3. The methyl protons of the acetyl group do not couple to H‐6, implying that this methyl group does not approach H‐6 closely. However, the 13C nucleus of this methyl group couples by +0.4 Hz to H‐5 and not to H‐3. This stereospecific five‐bond coupling implies that the acetyl group predominantly prefers an arrangement in which the carbonyl group lies trans to the other substituent, as would be expected electrostatically. Large twists out of the ring plane are not consistent with the observed couplings.
The 13C chemical shifts of 2′‐hydroxy‐substituted N‐benzylidene‐anilines and some N,N‐(o‐hydroxy‐benzylidene)diamines
Authors: Salman Salman R. , Al‐Rawi Jasim M. A. , Behnam George Q. 
Published: May 2005

Abstract13C chemical shifts of fourteen substituted 2′‐hydroxy‐N‐benzylidene‐anilines and three N,N‐(o‐hydroxy‐benzylidene)‐diamines are reported.
Structure of dibenzofuran and dibenzothiophene: Proton NMR study in nematic phases
Authors: Arumugam S. , Kunwar A. C. , Khetrapal C. L. 
Published: May 2005

AbstractProton NMR spectra of dibenzofuran and dibenzothiophene were investigated in the nematic phase of liquid crystals. Dipolar couplings obtained from the spectral analysis were used to derive the inter‐proton distance ratios. Deviations from planarity were observed in both molecules, and an attempt was made to determine the extent of non‐planarity. Differences in the relative inter‐proton distances in the two molecules are explained in terms of the bond polarization hypothesis and the van der Waals and the covalent radii of the oxygen and sulphur heteroatoms.
Unusual structural isomerization of monopropiophenone thiocarbonohydrazone
Authors: Rajendran G. , Jain Sampat R. 
Published: May 2005

AbstractMonopropiophenone thiocarbonohydrazone has been isolated in both linear and cyclic isomeric forms. Each form has been shown to isomerize and exist in equilibrium with the other in DMSO‐d6 solution by 1H and 13C NMR spectroscopy. The kinetics of this transformation show attainment of equilibrium in approximately 6 h, with a linear to cyclic configuration ratio of 40:60.
Tetraphenylporphyrin molecules containing heteroatoms other than nitrogen: 8—A carbon‐13 NMR study
Authors: Abraham Raymond J. , Leonard Paul , Ulman Abraham 
Published: May 2005

AbstractThe 13C NMR spectra of new hetero‐substituted tetraphenylporphyrin (TPP) molecules have been studied. It was found that most of the carbon chemical shifts are similar to those found in TPP. The similar chemical shifts of the different β‐carbons in S2TPP and in Se2TPP free bases and, moreover, the considerable downfield shift of the α‐carbons of the S(Se)‐rings on protonation are in agreement with the previously suggested theory of inner and outer aromaticity in these porphyrins.
Determination of enantiomeric excess by 13C NMR spectroscopy
Authors: Gogte V. N. , Nanda R. K. , Natu A. A. , Pandit V. S. , Sastry M. K. 
Published: May 2005

AbstractOxazolidine derivatives of β‐amino alcohols such as ephedrine have been resolved by 13C NMR spectroscopy using Eu(hfc)3 as a chiral shift reagent. The method is quantitative in the determination of enantiomeric excess, and is advantageous where 1H NMR is of limited use owing, for example, to significant line broadening.
Carbon‐13 NMR spectra of Piper alkamides and related compounds
Authors: Banerji Avijit , Sarkar (née Chaudhuri) Manjusha , Ghosal Tapasree , Pal Sudhir Chandra 
Published: May 2005

Abstract13C NMR spectra of Piper alkamides and related compounds have been completely assigned on the basis of splitting patterns in the coupled spectra, application of additivity relationships and internal comparison of chemical shifts.
NMR spectra of porphyrins. 26—conjugation versus steric repulsions in a planar chiral meso‐ Aminoporphyrin
Authors: Abraham Raymond J. , Smith Kevin M. , Bobe Frank W. , Minnetian Ohannes M. 
Published: May 2005

AbstractThe proton NMR spectra of the free base porphyrins γ‐meso‐dimethylaminopyrroetioporphyrin‐XV (1) and the corresponding γ‐diethylamino compound 2 show no temperature dependence, and are interpreted as being due to an essentially orthogonal conformation of the γ‐NR2 substituents. However, both of the corresponding dications 3 and 4, respectively, in CDCl3–TFA solution, give temperature‐dependent proton NMR spectra. Nuclear Overhauser enhancement difference spectra allow complete assignment of the spectrum of 3, and hence the interpretation of the temperature dependence. The spectra arise from a skew conformation of the NR2 groups in which the barrier to rotation through the orthogonal conformation is ca 13.6 kcal mol (56.8 kJ mol−1), and the barrier to rotation through the planar conformation is greater than this.
The NMR spectra of porphyrins. 27—proton NMR spectra of chlorophyll‐a and pheophytin‐a
Authors: Smith Kevin M. , Goff Dane A. , Abraham Raymond J. 
Published: May 2005

AbstractThe 500 MHz proton NMR spectra of chlorophyll‐a in several non‐aggregating solvents, at high dilution, are given and that of pheophytin‐a in CDCl3 at 360 MHz and at high dilution is reported. Under these conditions, the dispersion is such that separate resonances are observed and can be assigned for all protons in the molecules, except P‐5 to P‐15 in phytyl side‐chain. The complex spin systems of the C‐7 propionic ester side‐chains, and of the P‐1/P‐2 fragment, are analysed and the couplings obtained are interpreted in terms of possible conformations of the side‐chain.
Carbon‐13 NMR spectra and the method for their calculation for long‐chain polybranched carboxylic acids and their derivatives
Authors: Dostovalova V. I. , Terent'ev A. B. , Ikonnikov N. S. , Freidlina R. Kh. 
Published: May 2005

AbstractCarbon‐13 NMR spectra of 56 long‐chain polybranched carboxylic acids their esters, including chloroand acetoxy‐substituted derivatives, have been studied. An empirical linear two‐parameter equation, relating carbon chemical shifts in α‐branched carboxylic acids and their derivatives to the chemical shifts of the corresponding carbon atoms in analogous hydrocarbons, and to the degree of branching at the α‐carbon atom,

is suggested for the assignment of the signals, where δX is the shift in the acid (ester), δH the shift in its hydrocarbon counterpart and n the degree of branching. The regression coefficients, A, B and C, are given for X=COOH, COOMe and COOEt.It is shown that with polysubstituted derivatives, the equation may be applied sequentially. The secondary coefficients for the α‐substituent then depend on the nature of the substituent X entering the primary equation. The equation may, if necessary, be applied in combination with the additive and structural increments of halogen atoms.
Carbon‐13 nuclear magnetic resonance studies of some 9‐alkoxy‐ and 9‐alkylthio‐acridines
Authors: Faure R. , Galy J.‐P. , Mahamoud A. , Vincent E.‐J. , Galy A.‐M. , Barbe J. 
Published: May 2005

AbstractCarbon‐13 NMR parameters were determined for some 9‐alkoxy‐ and 9‐alkylthio‐acridines as solutes in DMSO‐d6 or D2O.
The assignment of diastereotopic menthyl groups by two‐dimensional NMR
Authors: Benn Reinhard 
Published: May 2005

AbstractThe 13C and 1H NMR spectra of (–)‐bis[1R, 3 R, 4S]menthylphosphine (1) are assigned by two‐dimensional double quantum NMR and 13C1H shift correlation diagrams. The variable temperature spectra of 1 indicate hindered rotation about the PC bonds.
13C NMR spectra of substituted phenazines: Substituent effects on carbon‐13 chemical shifts and the use of 13C15N coupling constants for the assignment of the aromatic carbons
Authors: Römer Axel 
Published: May 2005

AbstractThe 13C NMR spectra of 19 substituted phenazines have been measured. Substituent increments of the chemical shifts were calculated for methoxy, carbomethoxy and methyl derivatives. 15N‐Enriched phenazines were synthesized and nJ(13C15N) values were used for the assignment of the signals of the aromatic carbons.
Solvent dependence of the molecular structures of furan and thiophene determined by NMR of partially oriented molecules
Authors: Diehl P. , Jokisaari J. , Müller S. , Väänänen T. 
Published: May 2005

AbstractThe molecular rα structures of furan and thiophene dissolved in liquid crystals Merck ZLI 1167 and Phase IV were determined from the linear combinations of dipolar HH and CH coupling constants derived from the 1H and 1H13C satellite NMR spectra. Significant variations with the liquid crystal solvent are observed for both molecular structures. The deformations are particularly large in the case of thiophene and, surprisingly, in the normally well behaved ZLI 1167 liquid crystal.
NMR of some benzodiazepine drugs: Structure elucidation with lanthanide‐induced shifts of N‐1 substituted benzodiazepinones
Authors: Cazaux Louis , Vidal Christiane , Pasdeloup Maurice 
Published: May 2005

AbstractTwo 1,4‐benzodiazepinones of psychopharmacological interest, pinazepam (2) and prazepam (3), were studied in solution by 13C and 1H NMR. 1H variable‐temperature experiments showed that the seven‐membered ring exists in a simple pseudo‐boat form at room temperature, but the energy barrier is higher in 3 (ΔG405°c = 82.8 kJ mol−1) than in diazepam (1). Moreover, upon addition of LSR, the boat conformation is retained in the lanthanide ion‐substrate complex, as with 1 in the solid state. Using a concentration‐dependent shift technique and a computer‐assisted LIS method, the conformations of the N‐branched side‐chain were investigated. Two preferred orientations were found for the propargyl group of 2, while three unequally populated conformations of the cyclopropyl moiety of 3 are distributed preferentially in the sterically unhindered space around the complex.
Some INDO calculations of the dependence of one‐bond phosphorus‐phosphorus coupling upon molecular geometry
Authors: Duangthai S. , Webb G. A. 
Published: May 2005

AbstractSome INDO parameterized SCPT calculations of 1J(PP) and 1J(PP) are reported as a function of geometry. At structures corresponding to the gas‐phase equilibrium configuration of diphosphine, all of the substituted diphosphines considered are predicted to have negative values of 1J(PP). Both contact and non‐contact contributions to 1J(PP) are significant, whereas the angular variation of 1J(PP) is mainly due to the contact term. The non‐contact interactions are dominant in determining the value of 1J(PP).
Determination of acid dissociation constants of histidine‐containing peptides by proton magnetic resonance spectroscopy
Authors: Giralt Ernest , Viladrich Roser , Pedroso Enrique 
Published: May 2005

AbstractThe acid dissociation constant of the imidazolium ring of the decapeptide luliberin has been determined by 1H NMR‐followed titration in D2O. The normal procedure for the analysis of the titration curve, i.e. direct use of the Henderson‐Haselbalch equation, is still applicable in this case, but for more complex peptides a modified calculation procedure is proposed. Results obtained when both methods were applied to luliberin are compared. The influence of D2O when used as the solvent in this type of determination has been studied using Nα‐acetyl‐L‐histidine methyl ester as a model compound. The difference between the acid dissociation constant of this molecule determined in H2O and in D2O implies that a correction of −.25 unit is needed for those pKa values calculated by plotting the chemical shifts in D2O vs the apparent pH meter readings. The pKa found for Nα‐acetyl‐L‐histidine methyl ester, 6.30 ± 0.04, can be taken as a standard value for histidine‐containing peptides.
1H and 13C NMR spectra of 1‐palmitoyl‐2‐oleyl‐sn‐glycero‐3‐phosphorylcholine in CDCl3 solution and in sonicated dispersions in 2H2O
Authors: Santaren Juan F. , Rico M. , Ribera A. 
Published: May 2005

AbstractA mixed‐acid monounsaturated lecithin, 1‐palmitoyl‐2‐oleyl‐sn‐glycero‐3‐phosphorylcholine (POL), has been synthesized by phospholipase A2 digestion of 1,2 dipalmitoyl‐sn‐glycero‐3‐phosphorylcholine followed by reacylation of the lysolecithin with oleic anhydride.1H (90 MHz) and 13C (25.2 MHz) NMR spectra of POL in CDCl3 solution and in sonicated dispersions in 2H2O have been obtained, and spin‐lattice relaxation times measured. The relaxation times were characteristic of the type of structure formed and reflect molecular motion within the lecithin molecule in each structure. In both systems the spin‐lattice relaxation times increase along the alkyl chains towards the terminal methyl group, showing a corresponding increase in the chain molecular motion, although there are significant differences in the gradation of the changes.
Carbon‐13 NMR spectra of hydroxylated bile acid stereoisomers
Authors: Iida Takashi , Tamura Toshitake , Matsumoto Taro , Chang Frederic C. 
Published: May 2005

AbstractCarbon‐13 NMR signals were assigned for the complete set of the 26 theoretically possible isomers of methyl 5β‐cholanates having one to three hydroxy groups at positions C‐3, C‐7 and/or C‐12 in the nucleus. Substituent effects on the 13C NMR shielding data serving to characterize the position and configuration of the hydroxy groups are discussed.
1H NMR spectra and conformational analysis of some 1,4‐dithiepan‐6‐ones
Authors: Cook Michael J. , Ghaem‐Maghami Ghoabad , Kaberia Festus , Bergesen Knut 
Published: May 2005

Abstract1H NMR Parameters are reported for five 1,4‐dithiepan‐6‐ones. 1,4‐Dithiepan‐6‐one 1‐oxide exists in solution as an equilibrium involving two different twist‐chair conformations, which contrasts with its conformational behaviour in the solid state. Twist‐chair conformers are also adopted by other members of the series, the favoured form varying with ring substitution. The SO bond in 1,4‐dithiepan‐6‐one 1‐oxide and in its 5,5‐dimethyl analogue exhibit a preference for the pseudoaxial site.
1H NMR utilization of through‐space effects: III—configuration of oximes and analogous compounds
Authors: Rouillard M. , Girault Y. , Decouzon M. , Azzaro M. 
Published: May 2005

AbstractThe configurational assignment of Z and E nitrogen derivatives () of 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one was made taking into consideration the through‐space effects on oxime, O‐methyloxime, dimethylhydrazone, tert‐butylimine, N,N,N ‐trimethylhydrazonium iodide and oxime hydrochloride derivatives. The relationship between the magnitude of the chemical shifts of the α‐protons and the dihedral angle formed by the α‐CH bond and the CNOH plane was interpreted in terms of the geometrical dependence of the electric field effect. For the different Y substituents, the change in chemical shift between the Z and the E configuration of the proton near the functional group was mainly dependent on the electric field effect.
Recognition and assignment of meso and dl diastereomers: Dimethyl α,α′‐Dibromopimelate and N‐benzyl‐2,6‐dicarbomethoxypiperidine
Authors: Solladie‐Cavallo A. , Bouchet M. J. , Wermuth C. G. 
Published: May 2005

AbstractThe assignment of meso and dl diastereomers is carried out by NMR analysis of the signals due to the methylene protons in two simple cases, namely, dimethyl α,α′‐dibromopimelate (as an acyclic compound) and N‐benzyl‐2,6‐dicarbomethoxypiperidine (as a cyclic compound). In the case of the heterocyclic compound, an nσσ* hyperconjugative interaction between the CH bond α to the heteroatom and the lone pair of the heteroatom can be used, and leads to the same assignment.