bluuebunny/crossref_metadata_2025 huggingface dataset:
Configurational assignment by 13C NMR of stereoisomeric 3‐bromo‐3‐acyl derivatives of 5α‐ and 5β‐ androstane
Authors: Bégué J. P. , Bonnet‐Delpon D.
Published: May 2005

The configurational assignment of stereoisomeric 3‐bromo‐3‐acyl derivatives of steroids in both the 5α and 5β series has been carried out by comparing the 13C chemical shifts of C‐3. A downfield shift is observed for C‐3, bearing a bromine and an acyl group, on going from the isomer with an equatorial bromine to that with an axial bromine. This rule has been established by comparison of the 13C chemical shifts of model compounds in 4‐tert‐butylcyclohexanes of known configuration.
1H NMR spectroscopic determination of the isomeric ratios of bisphenol‐F diglycidyl ethers
Authors: Domke Wolf‐Dieter
Published: May 2005

1H NMR spectroscopy was used as a rapid method of determining the amount of the three possible isomeric forms of bisphenol‐F diglycidyl ether, one of the basic materials of epoxy resins for industrial applications. The complete spectral analysis of the glycidyl group, with respect to chemical shifts, coupling constants and magnetic anisotropy, made it possible to separate the overlapping signal regions by computational spectral simulation. Partial separation could also be obtained by application of the ‘Aromatic Solvent Induced Shift’ effect. A combination of both methods has been used successfully for the quantitative determination of the isomeric ratios of commercially available bisphenol‐F diglycidyl ethers.
Proton NMR spectroscopy of asymmetric benzylamines. The long‐range effects of an asymmetric environment
Authors: Jagur‐Grodzinski Joseph
Published: May 2005

1H NMR Spectra of the asymmetric benzylamines N‐benzyl‐N‐butyl‐2‐hydroxy‐1,3‐propandiamine, N‐benzyl‐N‐(2‐ethylhexyl)‐2‐hydroxy‐1,3‐propandiamine, N‐benzyl‐N‐butyl‐2,3‐epoxypropanamine and N‐benzyl‐N‐(2‐ethylhexyl)‐2,3‐epoxypropanamine, were analysed. A pronounced non‐equivalance of the benzylic hydrogens is induced by asymmetric carbons in γ position with respect to the benzylic group. [Δδ=0.2–0.3 ppm; J(AB)∼13.5 Hz]. Two sets of AB patterns were observed when two asymmetric carbons were present in the same molecule. RS+SR Diastereomers can thus be distinguished from the RR+SS enantiomers.
Standard values of vicinal coupling constants in the assignment of relative configurations and conformational analysis of acyclic chiral carbinols and hydrocarbons
Authors: Ibarra C. Alvarez , Romo M. T. Garcia , Perez M. S. Arias
Published: May 2005

Standard values of vicinal coupling constants are proposed in order to assign relative configuratations and analyse the conformational distribution of acyclic chiral carbinols and hydrocarbons. Thus, the assignment of relative configurations has been achieved for the diastereomeric carbinols, (2R4R, 2S4S)‐ and (2R4S, 2S4R)‐5,5‐dimethyl‐4‐phenyl‐2‐hexanol and (1R3R, 1S3S)‐ and (1R3S, 1S3R)‐1‐mesityl‐4,4‐dimethyl‐3‐phenyl‐1‐pentanol, through the analysis of the respective vicinal coupling constants and the corresponding conformational distribution. The analysis of the vicinal coupling constants allows the establishment of the monoconformational character of the (2R4S, 2S4R) diastereomer in the first case and the (1R3R, 1S3S) diastereomer in the second case.
Conformational and long‐range low field steric deuterium isotope effects on carbon chemical shifts
Authors: Pehk T. , Laht A. , Lippmaa E.
Published: May 2005

Comparison of the room and low temperature (203 K) 13C NMR spectra of 3‐cis‐bicyclo[4.4.0]decanone and its 2,2,4,4‐tetradeuterio isotopomer provides information about the deuterium isotope effect on the conformational equilibrium in this compound. Four‐bond low field deuterium isotope effects on some carbon chemical shifts are observed. These effects can be used for unambiguous assignment of the 13C lines to carbon atoms in alicyclic compounds.
Carbon‐13 NMR studies of 1‐aryl‐3‐phenyl‐2‐thioxo‐4‐imidazolidinones. Conformational isomerism and substituent effects
Authors: Colebrook Lawrence D. , Khadim Mohammad A.
Published: May 2005

Characteristic 13C chemical shift ranges and substituent shifts of heterocyclic ring carbon atoms have been identified for a number of 1‐aryl‐3‐phenyl‐2‐thioxo‐4‐imidazolidinones. 13CNMR spectra may be used to detect slow internal rotation about the aryl CN‐1 bond in compounds with diastereomeric rotational isomers; many corresponding carbon atoms in the rotamers have distinctly different chemical shifts. The δ‐effects originating from aryl ortho substituents are both electronic and steric in origin.
Carbon‐13 NMR studies of naturally occurring maytansinoids
Authors: Wallace William A. , Sneden Albert T.
Published: May 2005

The 13C NMR spectra of the antileukemic ansa macrolide maytansine and eight naturally occurring homologues were recorded. Signals were assigned to specific carbon atoms of the ansa macrolide ring and C‐3 ester side chain using data from off‐resonance decoupling, single frequency decoupling, and 180°–τ–907° double pulse experiments. The assignment of each carbon is discussed for maytansine and tabulated for the other eight maytansinoids.
Analysis and applications of 13C NMR lanthanide induced shifts of 1,4‐benzodiazepines
Authors: Paul H.‐H. , Sapper H. , Lohmann W. , Kalinowski H.‐O.
Published: May 2005

Lanthanide induced shifts using Yb(fod)3 and Pr(fod)3 were used for the signal assignments of the 13C spectra of the 1,4‐benzodiazepines diazepam, desmethyldiazepam, prazepam and flurazepam, and for characterizing their solution conformation with respect to the substituents at N‐1 and C‐5. The phenyl substituent at C‐5 is found to be nearly coplanar with the π‐bond between C‐5 and N‐4, and the substituents at N‐1 seem to be orientated towards the carbonyl group with dihedral angles of either 60° or 120° between the bonds N‐1 and C‐2 and C‐12 and C‐13. The metal ions seem to bind to O‐2 with metal‐oxygen distances between 0.19 and 0.26 nm and bond angles between 117° and 167°. Contact shifts induced by Pr(fod)3 are slightly larger than obtained for Yb(fod)3, whereas the latter reagent causes a stronger broadening.
1H and 13C NMR studies on 1‐methoxy‐endo‐tetracyclo[6.3.0.02,11.03,7]undec‐9‐ene
Authors: Jans A. W. H. , Lugtenburg J. , Cornelisse J. , Kruk C.
Published: May 2005

High field NMR spectroscopy, including nuclear Overhauser effect experiments and homonuclear decoupling techniques, provide conclusive evidence for the structure of 1‐methoxy‐endo‐tetracyclo[6.3.0.02,11.03,7]undec‐9‐enundec‐9‐ene. The 13C NMR spectrum has been recorded and the carbon shifts have been assigned by using SFORD spectra and selective decoupling experiments.
NMR study of bicyclopropylidene in the nematic phase at 400 MHz
Authors: Courtieu J. , Gounelle Y. , Jullien J. , Barnier J. P. , Conia J. M. , Kan S. K.
Published: May 2005

The eight spin NMR spectrum (400 MHz) of bicyclopropylidene oriented in a nematic phase has been analysed. The absolute signs and values of 5J(HH) long‐range spin‐spin coupling constants have been determined for the first time for this molecule. The ratios of interatomic HH distances have been deduced from the direct coupling constants.
Equilibria and barriers to interconversion between the syn and anti conformers in 9‐(o‐substituted phenyl)fluorenes obtained by photorearrangement of triptycenes
Authors: Tukada Hideyuki , Iwamura Michiko , Sugawara Tadashi , Iwamura Hiizu
Published: May 2005

The population ratios of the syn to the anti conformers in 9‐(2‐substituted phenyl)fluorenes have been determined by 1H NMR spectroscopy to range from 0.25 (for 2′;‐NH2) to >20 (2′;‐CHNNHC6H3(NO2)‐2,4). They appear to increase, firstly, with the steric bulk of the 2′;‐substituents and, secondly, with the electronic repulsion between the substituent and the π electrons on the fluorene ring. The unusually low population of the syn isomer in the 2′;‐NH2 compound was found by IR absorption to be due to stabilization of the anti form by NH …︁ π hydrogen bonding. Whereas the substituents on the fluorene ring do not affect the population of the two isomers in 9‐(2‐tolyl)fluorenes, the same series of substituents exhibit a positive slope in the Hammett plots of the equilibrium constants in 9‐(2‐methoxymethylphenyl)fluorenes. Through‐space interaction between the methoxymethyl group and the π‐donating fluorene ring is postulated. The free energy of activation (ΔG‡) for the interconversion between the two conformers in 9‐(2‐substitued phenyl)fluorenes have been obtained from the line‐shape depindence on temperatures. The ΔG‡ values ranged from 56.8 (for 2′‐NH2) ot 78.6kJ mol−1 when there is no fluorene ring substituent. IN three typical examples, a full line‐shape analysis gave, additionally, the ΔH‡ and ΔS‡ data of the interconversion. Introduction of a methyl group at position 1 of the fluorene ring raised. ΔG‡ by c. 13kJ mol−1.
Assignment of 13c chemical shifts in α‐pinene and pinanes following catalytic deuterium exchange
Authors: Forsyth David A. , Mahmoud Sabri , Giessen Bill C.
Published: May 2005

The 13C NMR chemical shifts of α‐pinene and cis‐ and trans‐pinanes have been reassigned on the basis of deuterium exchange experiments. Hydrogen at allylic positions in α‐pinene is exchanged for deuterium by treatment with D2 over an amorphous Pd‐Si alloy. Further reaction gives a mixture of pinanes labelled at four positions. The newly assigned shifts correspond well with other examples of confomationally dependent shifts in bicyclo[3.1.1]heptane derivatives.
Carbon‐13 NMR of oxygenated derivatives of polyoxyethylenes
Authors: Barrelle Michel , Béguin Claude , Tessier Sylvie
Published: May 2005

The 13C NMR spectra of several oligo(oxyethylene) glycols and of their derivatives obtained from oxidative cleavage were studied. Assignments are proposed and the 13C chemical shifts recalculated from sets of parameters obtained for the substituents on the parent structure, CH2CH2O.
Selective excitation of 13c resonances depending on the proton multiplicity
Authors: Beloeil Jean‐Claude , Le Cocq Christian , Lallemand Jean‐Yves
Published: May 2005

A new pulse sequence which allows selective excitations of carbons according to their multiplicity is described. The method is tested with an ionophorous antibioticthe sodium salt of lysocellin, C34H60O10.
Application of NMR spectroscopy of chiral association complexes 11—Rotation about the C(sp2)—C(aryl) Bond in 2,6‐Difluorobenzamides Studied by 19F NMR
Authors: Holǐk Miroslav , Turečková Milena , Mannschreck Albrecht , Stühler Georgine
Published: May 2005

The energy barrier to rotation about the C(sp2)C(aryl) single bond in non‐planar N,N‐dimethyl‐, N,N‐tetramethylene‐, N,N‐diisopropyl‐2,6‐difluorobenzamides and in N,N‐dimethyl‐2‐chloro‐6‐fluorobenzamide was investigated by 19F{1H} NMR in the presence of an optically active shift reagent. The free energy of activation was calculated from the coalescence temperature of the fluorine signals; the calculation was accomplished using the simple, approximative equation and, also, by the graphical procedure including the (eigen) line width, i.e. without the broadening caused by two‐site exchange. A distinct effect of the size of the N‐substituents on the ΔGc‡values was observed, in accordance with expectation.
Ordering in the nematic mesophase of a rapidly spinning sample
Authors: Teeäär R. , Alla M. , Lippmaa E.
Published: May 2005

The high resolution 13C NMR spectrum of an eutectic mixture of N‐(p‐methoxybenzylidene)‐p‐n‐butylaniline and N‐(p‐ethoxybenzylidene)‐p‐n‐butylaniline has been measured as a function of the spinning angle θ between the rotor axis and the magnetic field. The influence of a strong magnetic field and rapid sample spinning gives rise to a specific orientation of this nematic mesophase; if 0 < θ < 54°44′; the director of the nematic phase is oriented in parallel with the rotor axis, and if 54°44′; < θ <90° it is perpendicular to the rotor axis. At the exact magic angle a nematic sample displays the chemical shifts of the corresponding isotropic liquid. Nematic order is retained at all other director‐field angle values, thus allowing chemical shift anisotropy measurements of the nematic sample or of compounds dissolved therein.
The use of partially restricted molecular orbitals to investigate transmission mechanisms of spin–spin coupling constants. III—an INDO study of long‐range FH couplings in fluorinated derivatives of toluene
Authors: Facelli J. C. , Giribet C. G. , Contreras R. H.
Published: May 2005

Transmission mechanisms of long‐range FH couplings in several fluorinated derivatives of toluene are analysed carrying out partially restricted molecular orbital calculations at the INDO level of approximation. All π‐components follow the A+B sin2θ dependence, with the dihedral angle defined by the exocyclic CH (or CF) bond and the aromatic ring plane. Four‐ and five‐bond couplings show an important σ‐component, which follows the known zig‐zag rule. Both σ‐ and π‐contributions show a conspicuous insensitivity to fluorine ring substitution. Moreover, four‐bond couplings present an important through‐space component, which is negative for a cis arrangement. A sign inversion is found at a dihedral angle between 70° and 80°, which is interpreted as indicating that several through‐space mechanisms are operating.
N‐Nitrosodecahydroquinolines 3‐Nitrogen‐15 Nuclear Magnetic Resonance Spectra
Authors: Vierhapper Friedrich W. , Srinivasan Puliyur R.
Published: May 2005

15N Chemical shifts of N‐nitroso‐trans‐decahydroquinoline, N‐nitroso‐cis‐decahydroquinoline, of 12 methyl‐or t‐butyl‐substituted N‐nitrosodecahydroquinolines and of N‐nitroso‐trans‐syn‐trans‐perhydroacridine are reported. Shift effects for N‐nitrosation were calculated by comparison with the parent amines. Shift effects for ring substitution, obtained by comparison with the data of N‐nitrosopiperidine, are of similar direction and magnitude as in the parent amines for the ring nitrogens (N‐1). Methyl substitution nearly always causes deshielding for the nitroso nitrogens (N‐2), with a very large deshielding if the planarity of the (C‐α)2NNO region is disturbed.
Carbon‐13 chemical shifts and 1J(CH) coupling constants in 3,5 ‐ dehydrodiamantane
Authors: Hájek Milan , Třiska Jan , Isajev Sergej D. , Vodička Luděk
Published: May 2005

13C NMR spectra of 3,5‐dehydrodiamantane were compared with those of diamantanoid compounds with and without a cyclopropane ring. The effect of the cyclopropane ring in 3,5‐dehydrodiamantane is similar to that for the carbon atoms of 2,4‐dehydroadamantane and 2,4‐methano‐2,4‐dehydroadamantane, but not for 1,3‐dehydroadamantane. One‐bond coupling constants [1J(CH)] are discussed in terms of ring size and compared with bond angles. The observed difference between 1J(CH) of CH and CH2 groups of diamantanoid skeletons is connected with a change of the number of equatorial or axial positions of CH bonds in the cyclohexane ring.
Substituent effects on one‐bond 15N13C couplings in N,N‐dimethylanilines and nitrobenzenes. Effect of steric inhibition of conjugation
Authors: Axenrod T. , Watnick C. M. , Wieder M. J. , Duangthai S. , Webb G. A. , Yeh H. J. C. , Bulusu S. , King M. M.
Published: May 2005

The 1J(15N13C) values for a series of ring‐substituted N,N‐dimethylaniline‐15N derivatives and a series of nitrobenzene‐15N derivatives were measured from the 13C spectra. In the nitrobenzenes, small changes in 1J(15N13C) are attributed to the inductive effect of the substituents, since steric inhibition of conjugation has little effect on the magnitude of the coupling. In contrast, steric inhibition of nitrogen lone‐pair delocalization in N,N‐dimethylaniline derivatives markedly reduces the value of 1J(15N13C). Theoretical calculations of 1J(15N13C) values for the two series of compounds were made using standard INDO parameters and a ‘sum‐over‐states’ perturbation approach. Fair agreement between the calculated and experimental values is found.
Transmission of substituent effects—a CNDO approach. The influence of the internal electric field on the 29Si NMR substituent chemical shifts of phenyltrimethylsilanes and phenoxytrimethylsilanes
Authors: Wolff Renate , Radeglia Reiner , Ponec Robert
Published: May 2005

The 29Si NMR subtituent chemical shifts of 14 meta‐and para‐substituted derivatives of phenyltrimethyl‐and phenoxytrimethyl‐silanes have been interpreted in a uniform manner. They are shown to depend not only on the local but also on the non‐local parts of the charge distribution around the resonating nucleus. While the local part is taken into account by the paramagnetic screening constant, the influence of the non‐local part can be described by the induced internal electric field and additional higher order terms.
13C Chemical shifts and conformational equilibria in quaternary piperidinium salts
Authors: Sugiura Makiko , Takao Narao
Published: May 2005

Carbon‐13 nuclear magnetic resonance spectra of a series of N‐methyl‐N‐alkylpiperidinium salts have been measured, and the observed chemical shifts analysed in terms of the stereochemical and conformational properties of the molecules. Furthermore, the differences of the free energy (ΔG°) between two conformers on ring inversion have been estimated.
1H and 13C NMR spectral studies of C‐2 substituted isomeric exo‐ and endo‐5‐methyl‐bicyclo[3.2.1]octane‐6,8‐diones
Authors: Kasturi T. R. , Reddy S. Madhava , Murthy Parvathi S.
Published: May 2005

A detailed analysis of the 1H and 13C NMR spectra of C‐2 aryl and alkyl/desalkyl substituted isomeric exo‐ and endo‐5‐methylbicyclo[3.2.1]octane‐6,8‐diones is presented. The chemical shift of the C‐5 angular methyl, the C‐2 alkyl/olefinic (C‐10)/C‐2 methine protons, the aromatic proton shieldings and the characteristic AMX and ABX spectral pattern of the ketomethylene and bridgehead protons were found to be sensitive to the phenyl ring orientation (anisotropy). These distinctive features could be used for configurational distinction for this class of compounds. With increasing ortho‐methoxy substitution on the phenyl ring, considerable deshilelding of the bridgehead proton was observed (ca. 0.6 ppm). Absence of the C‐2 alkyl group in the desalkyl isomers resulted in substantial changes in the chemical shifts of different protons. A study of the NMR spectra of the corresponding bicyclic compounds with C‐2 methoxy/hydroxy substitution instead of the aryl group revealed that the anisotropy of the phenyl ring and the electronegative oxygen substituents have opposite effects.

The 13C NMR spectral assignment of each carbon resonance of C‐2 aryl and alkyl/desalkyl substituted isomeric exo‐ and endo‐5‐methylbicyclo[3.2.1]octane‐6,8‐diones and the corresponding C‐2 methoxy/hydroxy/chloro and methyl bicyclic compounds are reported. Additional ortho‐methoxy substitution on the phenyl ring was found to produce considerable high field shifts of the C‐10 and C‐1 carbon resonances. A high‐field shift was observed for the C‐6 and C‐8 carbonyl carbons, presumably due to 1,3‐dicarbonyl interactions. The chemical shifts of C‐1′ aromatic, C‐10 alkyl and C‐2 carbons, which are sensitive to exo/endo isomerism, could be utilized in differentiating a pair of isomers.
A convenient method of observing relatively broad nuclear magnetic resonances in the Fourier transform mode
Authors: Canet D. , Brondeau J. , Marchal J. P. , Robin‐Lherbier B.
Published: May 2005

A method is proposed for eliminating baseline distortions due to spurious ringings in Fourier transform NMR spectra involving broad resonances. It is based on the pulse sequence (π/2)–(Acquistion/Add)–π–τ–(π/2) (Acquisition/Subtract). τ is of the order of, or shorter than, the spectrometer recovery time. The sensitivity of the method is discussed.
Fluoro‐α‐amino acids. 1—use of 19F NMR spectroscopy for the configurational determination of β‐fluoro‐α‐amino acids through complexation by 18‐crown‐6 ether
Authors: Hamman S. , Salon M. C. , Béguin C.
Published: May 2005

Erythro and threo configurational assignments have been made for 11 β‐fluoro‐α‐amino acids or esters using the effect of complexation of the ammonium group by 18‐crown‐6 ether on the 19F NMR parameters. For the erythro configurations, 3J(HF) increases and a high‐field 19F chemical shift is generally observed; these phenomena are accompanied by a decrease in 3J(HH) and 3J(CF). The opposite effects are observed for the threo configurations. These observations can be explained by a change in the relative population of the conformers around the Cα‐Cβ bond on complexation of the ammonium group. This complexation impairs the interactions between the ammonium and fluorine groups and, concomitantly, the steric hindrance between the ammonium and R (methyl, phenyl or carboxylate) groups is increased.
77Se NMR study of some organic selenium compounds formed in the selenium dioxide oxidation of ketones
Authors: Laitalainen Tarja , Rahkamaa Erkki
Published: May 2005

77Se NMR chemical shifts and 1J(SeC) coupling constants were measured for nine organic selenium compounds: 4,5,6,7‐tetrahydro‐,4′,4′,6,6‐tetramethylspiro[1,3‐benzoxaselenole‐2,1′‐cyclohexane]‐2′,4,6′‐trione and closely related derivatives, bis(2‐hydroxy‐4,4,6,6‐tetramethyl‐3‐oxo‐1‐cyclohexenyl) selenide and derivatives, and 1,5,5‐trimethyl‐7‐selenabicyclo[2.2.1]heptane‐2,3‐dione. The chemicalshifts ranged from −107 to 595 ppm from the external dimethyl selenide standard. The bridged selenabicyclic compound showed a small coupling constant (42 Hz).
Compounds with bridgehead nitrogen. 42—1H NMR and stereochemistry of isomeric 6a‐methylperhydroindolo[3,2,1‐i,j]benzoxazines and the position of conformational equilibrium in perhydropyrrolo[1,2‐c][1,3]oxazine
Authors: Crabb Trevor A. , Newton Roger F. , Rouse Janet
Published: May 2005

The 1H NMR parameters of the NCH2O protons in the spectrum of perhydropyrrolo[1,2‐c][1,3]oxazine show its existence in solution at room temperature in the O‐inside cis‐fused conformation. rel‐(3aS,6aS,6bR,10aS,11aS)‐6a‐Methylperhydroindolo[3,2,1‐i,j]benzoxazine and rel‐(3aS,6aS,6bS,10aR,11aS)‐6a‐methylperhydroindolo[3,2,1‐i,j]benzoxazine are shown to adopt cis‐ and trans‐fused conformations, respectively, for the corresponding bicyclic moiety.
119Sn spin–lattice relaxation times and nuclear Overhauser enhancement factors in some organotin compounds
Authors: Blunden Stephen J. , Frangou Andrew , Gillies Duncan G.
Published: May 2005

Dipole‐dipole relaxation via non‐bonded protons is an important relaxation mechanism for119Sn in tri‐n‐propyltin and tri‐n ‐butyltin compounds. This causes a negative nuclear Overhauser effect, arising from the negative magnetogyric ratio, which in some cases nulls the signal. The relative contributions from the spin‐rotation and dipole‐dipole mechanisms vary: larger molecules have lower spin‐rotation and higher dipolar relaxation rates. The practical significance of large nuclear Overhauser enhancement factors in recording 119Sn spectra and the relation of the dipole‐dipole contribution to the molecular motion and of the spin‐rotation contribution to the absolute shift scale for 119Sn are discussed.
On the Karplus relation for 3J(POCC) of nucleotides
Authors: Davies David B. , Sadikot Husaini
Published: May 2005

The original Karplus parameters for analysing 3J(POCC) magnitudes of nucleotides in terms of conformational properties of the OC bond were taken from results for 3′,5′‐nucleotides and applied to 3′→ 5′‐oligonucleotides; the parameters were later modified to take account of ‘largey’ magnitudes of 3J(POCC) observed in 2′ → 5′‐oligonucleotides. In this work the origin of this discrepancy is explained in terms of substituent electronegativity effects at C‐1′, and quantified using the 13C NMR results of 2′,3′‐cyclic mononucleotides. A new set of Karplus parameters suitable for analysing 3J(POCC) magnitudes in 3′‐ and 5′‐nucleotides and 3′ → 5′‐oligonucleotides is determined from 13C NMR measurements on 3′‐nucleotides and available results for 3′,5′‐cyclic mononucleotides. A method of dealing with J(P, C‐1′) coupling in 2′‐nucleotides, 2′,3′‐cyclic nucleotides and 2′ → 5′‐oligonucleotides using the same Karplus relationship is suggested.
Temperature and solvent variation of the 13C and 1H NMR spectra of r‐1,t‐2,c‐3,t‐4‐tetrachlorotetralin
Authors: Bowmaker Graham A. , Calvert David J. , de la Mare Peter B. D. , Jones Alan J.
Published: May 2005

Vicinal coupling constants in the 1H and 13C NMR spectra of r‐1,t‐2,c‐3,t‐4‐tetrachlorotetralin change with temperature and solvent in a manner better explained by conformational equilibration than by intramolecular or solvent‐determined distortions.
Investigation of benzimidazoles. III—transmission of the substituent effects in 2‐substituted 1‐methylbenzimidazoles studied by 13C nuclear magnetic resonance
Authors: Lopyrev V. A. , Larina L. I. , Vakul'skaya T. I. , Shibanova E. F. , Titova I. A. , Voronkov M. G. , Liepin'sh E. E.
Published: May 2005

The influence of substituents on the 13C NMR chemical shifts of 2‐substituted 1‐methylbenzimidazoles has been investigated. The electronic effects of the substituents are transmitted to C‐4 and C‐7 mainly by the resonance mechanism, and to C‐5, C‐6 and N‐CH3, by approximately equal contributions of the resonance and inductive components. A critical analysis of the share in the transmission of substituent effects through the ‘pyridine‐type’ and ‘pyrrole‐type’ nitrogen atoms is given.
Nitrogen‐15 nuclear magnetic resonance spectroscopic study of compounds with nitrogennitrogen bonds
Authors: Yavari Issa , Roberts John D.
Published: May 2005

The 15N NMR spectra of several substances with nitrogen—nitrogen bonds have been obtained at the natural‐abundance level by high‐resolution NMR spectroscopy. Azo (NN) nitrogens are 300–500 ppm deshielded compared with hydrazo (NHNH) nitrogens. The sensitivity of the 15N shifts in these types of substances to substituent changes are reported, along with 15N–1H spin–spin couplings for some hydrazo compounds. Hydrogen‐bonding effects arising from solvent changes on the 15N shifts of azoxybenzene are different for its two kinds of nitrogen. The 15N NMR spectrum of N,N'‐dinitrosopiperazine in dimethyl sulfoxide at room temperature is consistent with the presence of two different conformations about the NNO bonds.
Compounds with bridgehead nitrogen. 44—the conformational analysis of perhydropyrido[1,2‐c] [1,3]thiazine
Authors: Crabb Trevor A. , Jupp Philip A. , Takeuchi Yoshito
Published: May 2005

The 270 MHz NMR data on trans‐ and cis‐(H‐4a, H‐7)‐7‐ethylperhydropyrido[1,2‐c][1,3]thiazine show heavy conformational bias to the trans‐ and S‐inside cis‐fused conformations, respectively. Comparison of the 13C NMR spectra of these anancomeric systems with the 13C NMR spectrum of perhydropyrido[1,2‐c][1,3]thiazine indicates a trans‐⇌S‐inside cis‐conformational equilibrium for the latter compound in CDCl3 at 25°C, containing ca 75% trans‐fused conformer. The 13C NMR spectrum of perhydropyrido[1,2‐c][1,3]‐thiazine at −75°C showed 64% trans‐fused conformer and 36% S‐inside cis‐conformer.
The conformation of t‐butyl 2‐methoxy‐5, 6‐dihydro‐2 H‐pyran‐6‐carboxylates and 6,6′‐ disubstituted 2‐methoxy‐5,6‐dihydro‐2H‐pyran derivatives on the basis of 1H and 13 C NMR spectra
Authors: Chmielewski Marek , Jurczak Janusz , Zamojski Aleksander , Adamowicz Halina
Published: May 2005

The 1H and 13C NMR spectra of trans‐ and cis‐tert‐butyl 2‐methoxy‐5,6‐dihydro‐2H‐pyran‐6‐carboxylates (1 and 2) and 6,6′‐disubstituted 2‐methoxy‐5,6‐dihydro‐2H‐pyrans (3‐7) have been recorded. HH and CH coupling constants are discussed in terms of the 1H6⇄6H1 conformational equilibrium. It has been found that 1 occurs exclusively in the 1H6 conformation, whereas its cis isomer, 2, exists in an equilibrium of both half‐chair forms. 6,6′‐Disubstituted 2‐methoxy‐5,6‐dihydro‐2H‐pyrans 3‐6 display spectral and conformational behaviour similar to that of 1, whereas 7 resembles 2 in this respect.
Rh NMR studies of organometallic rhodium(I) derivatives
Authors: Bonnaire R. , Davoust D. , Platzer N.
Published: May 2005

Organometallic rhodium(I) derivatives have been studied by 103Rh NMR. The chemical shift range extends from 609 ppm ([Rh.cp.cod]) to 2714.7 ppm ([Rh.fod.cod]). These results are supported by 13C and 31P NMR results, and give information about the bonding in these derivatives. Most of the complexes contain the cycloocta‐1,5‐diene ligand. For these complexes a linear correlation is observed between δRh and δC (olefinic carbons) (27 points, R = 0.960). For the phosphine derivatives a linear correlation is found between δRh and 1J(RhP) and, also, between δRh and parameters characterizing the basicity of the phosphine ligand. The correlation of δRh with ligand properties has been extended to a wider range of complexes by using the ‘influence parameters’ defined previously (10 points, R = 0.947). The sensitivity of δRh to steric factors is also proved.
1H and 13C chemical shift data of four peracetylated triglucoses. Application of two‐dimensional techniques
Authors: Bigler P. , Ammann W. , Richarz R.
Published: May 2005

1H and 13C chemical shifts are reported for four peracetylated triglucoses. Assignments are based on the recently proposed two‐dimensional Relayed Coherence Transfer Technique. The chemical shift data were obtained from conventional one‐dimensional NMR spectra.
Pairwise effects of chlorine substituents on the 13C NMR chemical shifts of dichlorobicyclo[2.2.1]heptanes (norbornanes)
Authors: Laihia Katri , Paasivirta Jaakko , Pikkarainen Heikki , Aho‐Pulliainen Sirkku
Published: May 2005

The 13C NMR spectra of nine dichlorinated bicyclo[2.2.1]heptanes (norbornanes) have been measured and assigned. The pairwise effects of chlorine substituents which cause deviations from the additivity of single‐substituent effects were investigated and are discussed. The largest effect found is the high‐field shift of carbons bearing vicinal cis substituents. In the case of geminal substitution deviations from additivity were found to be to low field and large in the γ, smaller in the β and negligible in the α chemical shifts. The observed deviations for 1,3‐disubstituted cases vary from −3.2 to +1.1 ppm at different carbons, allowing no simple explanation. Replacement of α‐hydrogen in a diaxial 1,3‐arrangement by CH3, OH or CI causes the single substituent effect, namely the γa effect, to change considerably.
Characterization of trisubstituted double bonds using 3J(CH)‐modulated spectra on simple NMR spectrometers
Authors: Highet R. J.
Published: May 2005

A simple sequence in which 13C precessions are allowed to develop with proton coupling for a period of 1/2 3J(CH) s before initiating decoupling and acquisition allows the determination of vicinal carbon–hydrogen coupling constants to facilitate the characterization of trisubstituted double bonds. The experiment is illustrated by studies of citraconic anhydride and limonene.
The 13C NMR spectra of 1,2,3‐triazolo[1,5‐a]pyridine and some monodeuteriated derivatives
Authors: Jones Gurnos , Sliskovic D. Robert
Published: May 2005

The 13C signals of 1,2,3‐triazolo[1,5‐a]pyridine (1) are assigned, using the corresponding 3‐, 6‐ and 7‐deuterio‐heterocycles; coupling constants are also given for compound 1.
1H NMR spectra of the 2‐trifluoroacetyl derivatives of benzo[b]furan and benzo[b]thiophene
Authors: Benassi Rois , Folli Ugo , Iarossi Dario , Schenetti Luisa , Taddei Ferdinando
Published: May 2005

The 1H NMR spectra of the 2‐trifluoroacetyl derivatives of benzo[b]furan and benzo[b]thiophene were recorded at 200MHz in two solvents, chloroform and acetone. A long‐range coupling constant, 5J(HF), between the fluorine nuclei of the trifluoroacetyl group and H‐3, of a value higher than 1 Hz, was measured. From the comparison of the 1H chemical shifts of, and the solvent effects on, the trifluoroacetyl compounds and those of the corresponding 2‐acetyl derivatives, and on the basis of an empirical interpretation of the 5J(HF) coupling constant, a predominant Z conformation was tentatively assigned to these derivatives.
Carbon‐13 NMR spectra of some 4‐substituted phenacyl bromides
Authors: Fujiwara Fred Yukio , Rittner Roberto , Freire Haydeé R.
Published: May 2005

The 13C NMR signals for some 4‐ substituted phenacyl bromides were assigned. The experimental chemical shifts of the aromatic ring carbons are in close agreement with those calculated using substituent chemical shifts. Both the carbonyl and the α‐methylene carbons exhibit upfield shifts compared with those of the corresponding 4‐substituted acetophenones.
Effect of collision interactions on 13C nuclear magnetic shielding in monosubstituted benzenes in halogen‐containing solvents
Authors: Jackowski Karol
Published: May 2005

The 13C nuclear magnetic shielding in benzene and ten monosubstituted benzenes was studied when these compounds were dissolved in cyclohexane, carbon tetrachloride, tetrachloroethylene, methylene bromide and methylene iodide. The results revealed that the observed changes of 13C magnetic shielding are dependent on both the solute and solvent molecular properties, although the dependence on the solvent is much more significant. It was also shown that the solvent effects for aromatic carbons are independent of the π electron density distribution in an aromatic ring. The observed 13C deshielding was attributed mainly to overlap effects which take place during molecular collisions.
A 1H and 13C NMR study of methoxyretinoids. Spectral assignment and determination of configuration
Authors: Ernst Ludger , Hopf Henning , Natsias Konstantin
Published: May 2005

A number of modified retinals and retinoic esters carrying one or two methoxy groups or one methoxy and one methyl group on the polyene chain were investigated by 1H and 13C NMR spectroscopy. Spectral assignments were made from homo‐ and selective 13C{1H} hetero‐decoupling experiments and from chemical shift comparisons. The configurations of the polyene double bonds were derived from vicinal H,H coupling constants, from 1H and 13C chemical shifts and by measuring nuclear Overhauser enhancements. It is found that all double bonds with no additional substituents occur in the trans (E) and all methoxy‐substituted double bonds in the cis (also E) configuration. Double bonds carrying methyl groups give rise to both cis (Z) and trans (E) isomers.
1H and 13C NMR studies of some germacrones and isogermacrones
Authors: Simova S. D. , Bozhkova N. V. , Orahovats A. S.
Published: May 2005

The 1H and 13C NMR spectra of the trans,trans‐, cis,cis‐ and cis‐C‐3–C‐4, trans‐C‐7–C‐8‐germacrones and of the cis‐C‐2–C‐3, trans‐C‐7–C–8, trans‐C‐2–C‐3, cis‐C‐7–C‐8‐ and cis,cis‐isogermacrones are analysed. The last two isogermacrones are new compounds. The C‐2–C‐3 double bond in the previously described isogermacrone is found to be of cis configuration, contrary to the hitherto accepted trans arrangement.
A 1H and 13C NMR study of carminic acid
Authors: Schmitt P. , Günther H. , Hägele G. , Stilke R.
Published: May 2005

The 1H and 13C NMR spectra of carminic acid were completely assigned, thus confirming its structure and the conformation of the glucose residue.
Rates and mechanisms of the intermolecular cation‐exchange reactions of sodium tetraphenylboron with sodium–nitrobenzene and with sodium–p‐nitrobenzonitrile
Authors: Atherton Neil M. , Blustin Peter H. , Humphreys Ceris A. , Shalabi Ahmed S.
Published: May 2005

The rates of the exchange of sodium ions between sodium tetraphenylborate and sodium–nitrobenzene or sodium–p‐nitrobenzonitrile were measured from analysis of the line broadening effect on the ESR spectra off the paramagnetic ion pairs. The rate is significantly lower for the substituted nitro compound, and it is suggested that this reflects a difference in mechanism for the two systems.
Substituent effects on 33S NMR chemical shifts in sulphones
Authors: Cassidei L. , Fiandanese V. , Marchese G. , Sciacovelli O.
Published: May 2005

The 33S NMR spectra of some selected sulphones demonstrate additive substituent‐induced chemical shift (SCS) effects. In dimethyl sulphone (1), replacement of a methyl group by a vinyl or a phenyl group causes an SCS effect of −7 to −8.5 ppm or −4 to −5 ppm, respectively. The 33S chemical shift in 1 is also sensitive to substitution of methyl protons. The ß‐substituent effect for methyl and phenyl groups is in the range +7 to +8 ppm and +5.5 to +6 ppm, respectively.
Conformational analysis of rigid enol‐ethers by proton nuclear magnetic resonance
Authors: Durand R. , Geneste P.
Published: May 2005

Z,E isomers of rigid enol‐ethers were studied by proton nuclear magnetic resonance. As with oximes, it was found that the chemical shift difference (Δδ=δz−δE) for the protons α to the function in question depends on the dihedral angle between the CαH and CC bonds. This phenomenon can be explained by an electric field effect and not by a magnetic anisotropy effect. The present study has allowed the derivation of values of the volume magnetic susceptibility and the product of b×the dipole moment for the CO bond.
On the chemistry of pyrrole pigments: 57—Phytochrome model studies: Complete assignments of the 13C NMR spectra of phytochrome model compounds
Authors: Falk Heinz , Müller Norbert , Vormayr Günther
Published: May 2005

A strategy for the assignment of aromatic 13C NMR resonances of pyrrole pigments is presented which makes use of two‐dimensional chemical shift correlation spectroscopy via one‐bond and long‐range C,H coupling constants. The complete 13C NMR assignments for a 3,4‐dihydropyrromethenone and three phytochrome model compounds (2,3‐dihydrobilatrienes‐abc) are given.
Nuclear magnetic 13C19F double resonance: Fluorine broad band decoupling
Authors: Sklenář Vladimír , Starčuk Zenon
Published: May 2005

The feasibility of broad band fluorine decoupling for 13C NMR spectroscopy, employing a new composite pulse sequence, is shown. The application of this sequence allows the decoupling of fluorine nuclei over almost the total range of chemical shifts in fluoroorganic compounds, at magnetic fields of up to 2.3 T, without extensive demands on the decoupler power amplifier. The range of expected chemical shifts of fluorine bonded to carbons is briefly discussed.
Carbon‐13 NMR spectra of some phosphorane‐amino compounds
Authors: Costanzi Fabio , Pianca Maurizio , Tatò Marco , Moggi Giovanni
Published: May 2005

The 13C NMR spectra of a series of compounds of the type R1P(NR22)nPh3−n X− are reported. A net trend toward larger 1J(PC) values with an increasing number of dialkylamino substituents is observed.
Carbon‐13 nuclear magnetic resonance spectra of some heterocyclic D‐homoandrostanes
Authors: Marcano Deanna , De Méndez Jeannette , Ortiz Ana C. , Salinas Mirna
Published: May 2005

The 13C chemical shift data of several D‐homoandrostanes with heteroatoms (N,O) in the 17a‐position are reported. Heteroatom effects on the shieldings of the carbons of rings C and D are discussed.
1H and 13 NMR data of 1,2‐epoxymenthane derivatives
Authors: Gács‐Baitz Eszter , Kalaus György , Györy Péter
Published: May 2005

The NMR data of epimeric pairs of subsituted 1,2‐eposymenthane derivatives are reported.
Carbon‐13 NMR spectra of some phenanthrene derivatives from Aristolochia indica and their analogues
Authors: Achari Basudeb , Bandyopadhyay Soumitra , Chakravarty Ajit K. , Pakrashi Satyesh C.
Published: May 2005

13C NMR spectra of compounds related to aristolochic acid and aristololactam, the constituents of Aristolochia indica, have been studied to determine the chemical shifts and coupling constants of polysubstituted phenanthrenes. Selective 1H decoupling and long‐range couplings were utilized for the assignments. Substituent‐induced chemical shifts and also the effects on coupling constants could be deduced in some cases. Anion formation was found to be particularly helpful in the interpretation of the spectra of carboxylic compounds. Shift assignments of some structurally related compounds could also be made.
1H and 13C NMR study of vinyl chloride telomers with carbon tetrachloride
Authors: Bessière J. M. , Boutevin B. , Taha M. , Vial F.
Published: May 2005

The 1H and 13C NMR spectra of some vinyl chloride telomers have been analysed.
Correlation of apparent myelin measures obtained in multiple sclerosis patients and controls from magnetization transfer and multicompartmental T2 analysis
Authors: Tozer D.J. , Davies G.R. , Altmann D.R. , Miller D.H. , Tofts P.S.
Published: May 2005

Two relatively new techniques purport to give measures of the myelin content of brain tissue. These measures are the myelin water fraction from multicompartmental T2 analysis, and the semisolid proton fraction from analysis of magnetization transfer (MT). The myelin water fraction is the fraction of signal with a T2 of less than 50 ms measured from a 32‐echo sequence. It is believed to originate from water trapped between the myelin bilayers. The semisolid proton fraction is thought to include protons within phospholipid bilayers and macromolecular protons, and may also be a measure of myelin content. Multicompartmental T2 and MT imaging were carried out on controls and patients with multiple sclerosis (MS), and estimates of the semisolid proton and myelin water fractions were obtained from white matter (WM), gray matter (GM), and MS lesions. These were then correlated for each tissue and subject group. Positive correlations were seen for MS lesions (r ≈ 0.2) and in WM in patients (r = 0.6). A negative correlation (r ≈ −0.3) was seen for GM. These results indicate that the two techniques measure, to some extent, the same thing (most likely myelin content), but that other factors, such as inflammation, mean they may provide complementary information. Magn Reson Med 53:1415–1422, 2005. © 2005 Wiley‐Liss, Inc.
Self‐navigated multishot echo‐planar pulse sequence for high‐resolution diffusion‐weighted imaging
Authors: Nunes Rita G. , Jezzard Peter , Behrens Timothy E. J. , Clare Stuart
Published: May 2005

Single‐shot techniques have preferentially been adopted for diffusion‐weighted imaging due to their reduced sensitivity to bulk motion. However, the limited spatial resolution achievable results in orientational signal averaging within voxels containing a distribution of fibers. This leads to impaired performance of tracking algorithms. To combat partial volume effects, high‐resolution multishot techniques can be used but, being more sensitive to motion, require phase correction to obtain artifact‐free images. While separately acquiring 2D navigator echoes is an effective approach, it is not very efficient as the navigators do not contribute signal to the final image. Here a self‐navigated interleaved echo planar imaging (EPI) sequence based on EPI with keyhole (EPIK) is proposed. The refocusing reconstruction method is successfully adapted to EPIK and compared to the standard linear approach. The resultant improvement in resolution is shown to lead to a significant increase in anisotropy in fiber‐branching areas and can potentially offer a superior ability to detect fine tract splits. Magn Reson Med 53:1474–1478, 2005. © 2005 Wiley‐Liss, Inc.
Botulinum toxin therapy in hemifacial spasm: Clinical and electrophysiologic studies
Authors: Geller Bruce D. , Hallett Mark , Ravits John
Published: May 2005

Three patients with idiopathic hemifacial spasm were studied clinically and electrophysiologically before and after injections of botulinum toxin into the involved periocular and facial muscles. The spasms were improved for approximately 3 months, and the effect was repeatable on reinjection. The spasms diminished only as long as the muscles were clinically weak, and spasms were observed electromyographically even though therapy eliminated the clinical spasms. Uninjected muscles continued to have spasms. Transmission of excitation from the zygomatic branch to the marginal mandibular branch of the facial nerve and vice versa in all patients was unaltered after therapy, but the amplitude of the response was decreased. The efficacy of botulinum toxin in hemifacial spasm appears to be related to the production of muscle weakness; there is no demonstrable effect on phenomena believed to be ectopic excitation or ephaptic transmission in the facial nerve.
Effect of chain length on nuclear quadrupole interaction of nitrogen‐14 in aminated n‐alkanes
Authors: Murgich Juan , Santana R. Magaly
Published: May 2005

The 14N nuclear quadrupole resonance (NQR) spectra of several aminated n‐alkanes of the type CH3(CH2)xNH2(CH2)xNH2 at 77 K are reported and analysed in the framework of a semi‐empirical theory. The NQR data presented oscillations for x<6 and reached limiting values for x≥6. The results obtained are discussed in terms of inductive and conjugative effects, as well as the possible contributions of the hydrogen bond network presented in the solid state.
1H NMR spectra of diastereomeric 1,4‐disubstituted 2,3‐diphenylbutanes; examples of ABXX′ A′B′ and A2XX′A2′ spin systems
Authors: Spassov S. L. , Berova N. D. , Hawkes G. E. , Randall E. W.
Published: May 2005

The 1H NMR spectra of the meso‐ and (±)‐forms of some 1,4‐disubstituted 2,3‐diphenylbutanes were measured at 400 MHz. The spectral parameters were determined by iterative computer analysis, treating the protons as ABXX′A′B′ or (in some cases) A2XX′A2′ systems.
The antarctic lichens: 1—The stereochemistry of 7β‐acetoxy‐22‐hydroxyhopane from Pseudocyphellaria freycinettii, indigenous to S. Georgia
Authors: Howarth O. W. , Rickard T. M. A. , Sainsbury M.
Published: May 2005

From differential spin decoupling and nuclear Overhauser enhancement experiments, the 400 MHz 1H NMR spectrum of the triterpene 7β‐acetoxy‐22‐hydroxyhopane is interpreted to establish the α‐configuration of the side‐chain at C‐21.
13C NMR chemical shifts of thiols, sulfinic acids, sulfinyl chlorides, sulfonic acids and sulfonic anhydrides
Authors: Freeman Fillmore , Angeletakis Christos N.
Published: May 2005

13C NMR spectra of thiols, sulfinic acids, sulfinyl chlorides, sulfonic acids and sulfonic anhydrides have been obtained. The data are discussed in terms of the additivity of the deshielding effects exerted by the sulfur functionality at the α‐ or β‐position, and the shielding effects produced by the sulfur function at the γ‐position.
Conformational analysis: XXI—1H NMR study of 4,5‐dimethyl‐, 2,4,5‐trimethyl‐ and 2,2,4,5‐tetramethyl‐1,3‐dithiolanes
Authors: Pihlaja Kalevi , Keskinen Raimo , Eskonmaa Mauri , Nurmi Timo
Published: May 2005

The 60 MHz 1H NMR spectra of seven differently substituted 4,5‐dimethyl‐1,3‐dithiolanes have been recorded and analysed. Configurational assignments are made and conformational aspects are discussed in the light of the spectral parameters.
13C Nuclear magnetic resonance spectroscopy of biliverdin IX dimethyl esters and related compounds
Authors: Petrier Christian , Dupuy Claude
Published: May 2005

The 13C NMR spectra of differently substituted or conformationally restrained biliverdins have been recorded. Certain characteristics are found for these tetrapyrrolic systems, i.e. the chemical shifts of the methine bridge carbons, the vinyl groups and the bis‐lactam form. This study, in conjunction with other spectroscopic data, may be used to assign the structures of biliverdins IX αβγλ, phorcabilin, isophorcabilin and neobiliverdin IXλ.
Substituent and solvent effects on the 19F chemical shifts of 3‐ and 4‐XCH2‐substituted fluorobenzenes
Authors: Happer D. A. R. , Steenson B. E. , Newman R. H.
Published: May 2005

Substituent effects on the 19F chemical shifts of a series of 3‐ and 4‐XCH2‐substituted fluorobenzenes have been studied in five different solvents (dimethyl sulphoxide, acetone, chloroform, carbon tetrachloride and benzene). The results show that in both series substituent effects (other than inductive effects) contribute in at least some cases to the overall shifts, but that these showed little solvent dependence. The meta series showed a proportionately greater solvent dependence than the para series, and this is attributed to the greater importance of ‘through solvent’ direct field effects in the former.
Carbon‐13 NMR spectra of taxane‐type diterpenes: Oxiranes and oxetanes
Authors: Rojas Anibal C. , De Marcano Deanna , Méndez Bernardo , de Méndez Jeannette
Published: May 2005

The 13C NMR spectra of a series of nine taxane derivatives are reported. A detailed analysis of the assignments is presented. Observed long‐range substituent effects are explained on the basis of the proximity of rings A and C in this type of molecules.