bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon‐13 chemical shifts of 3‐substituted thietanes, thietane 1‐oxides and thietane 1,1‐dioxides
Authors: Dittmer Donald C. , Patwardhan Bhalchandra H. , Bartholomew John T.
Published: May 2005

Carbon‐13 chemical shifts of the α‐ and β‐carbon atoms for 12 thietane 1,1‐dixides, 9 thietane 1‐oxides and 7 thietanes with a variety of 3‐substituents [H, CH(CO2Et)2, SEt, Br, SPh, Ph, Cl, NMe2, OH, OSiMe3, OAc, OEt] are correlated according to the nature of the sulfur atom (Y=sulfone, sulfoxide, sulfide) and the nature of the 3‐substituent (X) by the equations δα= aY+bX and δβ=aX+bY, where a and b are parameters characteristic of X and Y. One‐bond coupling constants [J(CH)] are reported for 21 compounds. The chemical shifts for the α‐ and the β‐carbon atoms of the sulfones show the ‘fore‐membered ring sulfone effect’ (α‐carbon unusually deshielded, β‐carbon unusually shielded), but the α‐carbon‐hydrogen coupling constants are similar to those of the sulfoxides and sulfides; the β‐carbon‐hydrogen coupling constants are sensitive to the nature of the substituent (X) but no special β‐effect is observed. Comparison of the chemical shifts of the α‐methylene carbon atoms of 3‐phenyl‐, 3‐(β‐naphthyl)‐ and 3‐(α‐thienyl)‐thietes with those of the coresponding sulfones also reveals the ‘four‐membered ring sulfone effect’ cis‐ and trans‐3‐Substituted thietane 1‐oxides may be distinguished by the greater downfield shift for the β‐carbon atom in the trans‐isomer.
A new method for differentiating between solvent effect mechanisms on 13C chemical shifts
Authors: Sugiura Makiko , Takao Narao , Ueji Shinichi
Published: May 2005

A new method of differentiating between the different mechanisms operative for 13C solvent effects is proposed. This approach, in which the 13C solvent shifts of C‐1 of tert‐butylcyclohexane are selected for the reference solvent shifts, allows the study of 13C solvent shifts measured from an internal TMS reference. Using this method, the solute factor related to the van der Waals contribution can be estimated, and specific solvent effects other than the van der Waals effect can also be detected.
Relationships between the acidity of the Z and E isomers of N‐Nitroso‐N‐alkyl‐α‐amino acids and their conformations
Authors: Liberek Bogdan , Ciarkowski Jerzy , Plucińska Krystyna , Stachowiak Krystyna
Published: May 2005

The acidity constants of both Z and E conformational isomers of five N‐nitroso‐N‐alkyl‐α‐amino acids, ONN(R1)CH(R2)COOH, are determined by the observation of selected pH titrated 1H NMR signals. For two glycine derivatives (1, R1CH3, R2H, ONSar; 2, R1C2H5, R2H, ONEtGly) and two alanine derivatives (3, R1CH3, R2CH3, ONMeAla; 4, R1C2H5, R2CH3, ONEtAla) the E isomers appear to be stronger acids than the Z while for the third alanine derivative (5, R1n‐C3H7, R2CH3, ONPrAla) the opposite is observed. These results, also including anisotropy effects associated with the NNO group, are discussed in terms of conformations. A 7‐membered ring conformation with an NO…HOOC intramolecular hydrogen bond is proposed to be statistically important in the Z isomers of 1, 2, 3 and, to a lesser extent, 4.
1H NMR investigations on the conformation of the spirodioxolanes derived from vicinal diols. II—The ketal of cyclohexanone and racemic 1,2‐propanediol
Authors: Csunderlik C. , Chirilǎ T. , Bacaloglu R.
Published: May 2005

The methylene, methine and methyl protons at C‐2 and C‐3 from the dioxolane moiety in 2‐methyl‐1,4‐dioxaspiro[4.5]decane constitute an ABMX3 coupling system. The analysis data obtained and, also, the application of the Karplus rule to the value of the J(AB) vicinal coupling constant, confirm the axial orientation of the A methine proton and the pseudoequatorial orientation of the B methylene proton. These findings agree with a ‘half‐chair’ conformation of the 1,3‐dioxolane ring.
NMR spectrum of benzo[b]furan in a nematic phase
Authors: Arumugam S. , Kunwar A. C. , Khetrapal C. L.
Published: May 2005

The proton NMR spectrum of benzo[b]furan has been investigated in the nematic phase of a liquid crystal. Dipolar couplings obtained from the spectral analysis have been used to derive the interproton distance ratios. The phenyl ring geometry differs from that in benzo[b]thiophene. The deviations have been explained in terms of bond polarization effects.
13C NMR study of some derivatives of 1,3,4‐oxadiazoles, 1,3,4‐thiadiazoles and isosydnones
Authors: Aranda Gérard , Dessolin Michèle , Golfier Michel , Guillerez Marie‐George
Published: May 2005

The assignment of all ring carbons of 37 derivatives of 1,3,4‐oxa‐ or thiadiazoles and of seven isosydnones is described. In some cases, 13C‐labelled compounds were used. The analysis of substituent effects and the calculation of charge densities of some of the derivatives suggest that the two nitrogen atoms form a protective screen against electron perturbation and play the role of an ‘electronic buffer’. A notable variation of chemical shifts could be observed only when oxygen is replaced by sulphur.
The combined effects of two chlorine substituents and the non‐additivities of chemical shifts in aliphatic dichloro esters
Authors: Pitkänen Maija
Published: May 2005

Carbon‐13 NMR spectra were measured for 25 methyl esters of aliphatic dichlorocarboxylic acids for substituted propanoic to hexanoic acids. Observed 13C shifts are compared with calculated shift values obtained from the shifts of the corresponding monochloro esters by applying a simple sum method. The greatest failures from additivity are observed for αβ and αα substituted carbons. The combined effects of two chlorine substituents were determined, and compared with those obtained from chlorine substituent effects in monochloro esters by assuming additivity. The trends displayed by the combined effects, and also by the non‐additivity effects, are discussed.
Configurational and conformational studies of N,N‐dimethylpiperidinium derivatives by 13C and 1H NMR spectroscopy
Authors: Casy A. F. , Ogungbamila F. O.
Published: May 2005

The 13C and 1H NMR spectra of a series of methiodides of mono‐ and di‐C‐methyl derivatives of 1‐methyl‐4‐phenyl‐4‐piperidinols are reported and chemical shift data analysed in terms of configurations and conformations of isomeric sets. Results demondtrate the value of quaternary salt NMR data as an aid to configurational assignment, and the evaluation of non‐bonded interactions governing conformational equilibria in piperidine derivatives.
Isotopic perturbation of a degenerate valence isomerization. A 13C NMR study of deuterio‐1,5‐dimethylsemibullvalene
Authors: Askani Rainer , Kalinowski Hans‐Otto , Weuste Burkhard
Published: May 2005

Mono deuterio‐1,5‐dimethylsemibullvalene is studied by the isotopic perturbation method with respect to the equilibrium of the valence isomerization. It emerges that deuterium prefers the cyclopropane position. From the temperature dependence of the splittings in the 13C NMR spectra the ground state enthalpy difference in mono deuterio‐1,5‐dimethylsemibullvalene is calculated to be 484 J mol−1.
Chemistry of the SO Bond. 8—A stereochemical investigation of some methyl‐substituted trimethylene sulphites (1,3,2‐Dioxathian 2‐Oxides) via 13C nuclear magnetic resonance
Authors: Hellier Desmond G. , Phillips Andrew M.
Published: May 2005

13C NMR chemical shifts for trimethylene sulphite and 35 derivatives are presented. From the magnitudes of the β shifts it has been possible to establish chemical shift additivity relationships for a series of compounds. The results are discussed in terms of probable conformations in solution.
Study of different association processes in the bicyclo[3.2.1]octan‐3‐ol series by 13C relaxation time measurements
Authors: Zahra J. P. , Waegell B. , Faure R. , Vincent E. J.
Published: May 2005

The measurements of T1 relaxation times in 13C NMR spectroscopy are used to determine solute‐solvent interactions. endo‐ and exo‐Bicyclo[3.2.1]octan‐3‐ol and the corresponding bromohydrins are used as substrates. In a non‐polar solvent, such as cyclohexane, solute‐solvent interactions occur exclusively, whereas in the more polar acetone only solute‐solvent interactions are observed. In chloroform, which is of intermediate polarity, the two types of interactions (solute‐solute and solute‐solvent) occur simultaneously.
Determination of optimal parameters in the convolution difference resolution enhancement technique
Authors: Roth K. , Kimber B. J.
Published: May 2005

The relationship between the relative resolution, sensitivity and line distortion of convolution difference spectra and the values for the adjustable parameters k and n is investigated. A practical guideline for obtaining optimum results is given.
The interaction between paramagnetic relaxation reagents and carbon tetrachloride
Authors: Edlund Ulf , Grahn Hans
Published: May 2005

The 13C spin‐lattice relaxation times for carbon tetrachloride have been measured in the presence of various paramagnetic chromium (III) chelates (PARRs). The T1 values were compared with those of an inert standard, cyclohexane. A specific PARR: carbon tetrachloride interaction was clearly indicated, which is less obvious for bulky ligands or ligands having electron‐withdrawing substituents. The electron‐nuclear relaxation model and the quantitative description of outer‐sphere complexation is briefly discussed.
Determination of the stereochemistry of the monomethylated homologues of 1‐chloro‐ and 1‐bromo‐1‐methylcyclobutane by means of NMR spectroscopy
Authors: Hittich Reinhard
Published: May 2005

The 300 MHz 1H NMR spectra of 1‐chloro‐ and 1‐methylcyclobutane and all monomethylated homologues are reported and analysed with regard to the ring conformations. The results indicate that halogen substituents in methylated halocyclobutanes have a greater preference for the pseudo equatorial position than do methyl groups. The 13C NMR spectral data are given, and substituent parameters for halogen substituents and methyl groups are calculated. Of note are the variable γ effects, especially the remarkable difference between the γ‐methyl effects of the stereo‐isomeric 1,3‐substituted cyclobutane compounds.
An NMR, ESR, ENDOR and TRIPLE resonance investigation of a cation radical formed from 1,2,4,5‐tetramethoxybenzene
Authors: Fairhurst S. A. , Smith I. M. , Sutcliffe L. H. , Taylor S. M.
Published: May 2005

Several methods have been established for preparing cation radicals from 1,2,4,5‐tetramethoxybenzene that allow highly resolved ESR spectra to be recorded. Precise values of the hyperfine coupling constants for the aromatic and methoxy protons have been obtained; the values are 0.2268±0.0004 and 0.0863±0.0002 mT, respectively, with dichloromethane as solvent. No temperature dependence is evident. TRIPLE resonance experiments showed that both coupling constants have the same sign. NMR experiments provided contact shift and line broadening measurements; these proved that both the above constants are positive and led to a value of 3.1 (±0.3)×108M−1 s−1 at 23°C for the rate constant for electron exchange between the cation radical and the parent compound.
Application of NMR spectroscopy of chiral association complexes. 12—rate determination of an intramolecular motion in a free molecule by means of dynamic NMR measurements in the presence of an auxiliary compound
Authors: Küspert Reinhard , Mannschreck Albrecht
Published: May 2005

The rate constants of intramolecular processes can sometimes be measured only in the presence of optically active auxiliary compounds. The problem of obtaining the rate for the free molecule was solved by linear extrapolation of rate constant from the complexed to the uncomplexed molecule (LERCUM). This method is developed theoretically and checked experimentally. 2‐Bromo‐2‐methyl‐1‐(3‐bromo‐2‐methoxy‐4,5,6‐trimethylphenyl)‐1‐propanone has the advantage that rotation about its carhonyl‐to‐aryl bond can be measured both in the presence of (+)−2,2,2‐trifluoro‐1‐phenylethanol as well as in the absence of an auxiliary compound. The novel method of extrapolation is confirmed by the agreement between both results.
13C NMR spectral study of polyacetoxyxanthones. IV—13C NMR spectroscopy of substituted xanthones
Authors: Chaudhuri R. K. , Frahm A. W.
Published: May 2005

The 13C NMR chemical shifts of nine acetoxyxanthones are reported and identified. The acetoxy substituent effects have been evaluated and the corresponding shift increments proposed.
High resolution 13C and 1H NMR spectral analysis of 1‐azafluorene
Authors: Fomichov A. A. , Svoren V. A. , Golovtsov N. I. , Soldatenkov A. T. , Prostakov N. S.
Published: May 2005

An analysis of the 1H and 13C spectra of 1‐azafluorene has been carried out using computer calculations and homo‐ and heteronuclear double resonance techniques. The 4J, 5J and 6J long‐range coupling constants of the 9‐CH2 group protons with the protons of the pyridine and the phenylene rings have been observed and measured. The long‐range J(CH) values in the 1H coupled 13C spectrum have been assigned and measured on a first‐order basis.
Studies on olefins. IX—proton NMR study of some CH2CR1R2 and CHR3CR1R2 alkenes
Authors: Rummens Frans H. A. , Lomas John S. , Tiffon Bernard , Coupry Claude , Lumbroso‐Bader Nicole
Published: May 2005

The proton NMR spectra of 2,3,4,4‐tetramethyl‐3‐t‐butylpent‐1‐ene rotarners have been completely assigned by low temperature NOE measurements. Chemical shifts and cis and trans allylic coupling constants are unambiguously determined. It is shown that other 2‐substituted propenes can be assigned on the basis of the coupling constants, but not from the chemical shift data. In 1,2‐disubstituited propenes, however, the transoid coupling constant falls in the range of the cisoid coupling constant values of the 2‐substituted propenes. Coupling constants cannot, therefore, be used in the 1,2‐disubstituted propene series as a criterion for determining structure.
NMR chemical shift method in magnetic susceptibility measurements applied to studies of the reaction of cobalt complexes with cumene hydroperoxide
Authors: Trzeciak A. M. , Ziółkowski J. J.
Published: May 2005

The NMR chemical shift method was applied for the determination of the magnetic susceptibility of paramagnetic transition metal complexes in solution. The method was found to be very useful for the determination of magnetic susceptibility changes during a chemical reaction in which one paramagnetic compound produced another. The concentrations of two paramagnetic cobalt complexes [Co3O(O2CCH3)6(HO2CCH3)3] and Co(O2CCH3)2, were calculated from the chemical shift value observed during their reaction with cumene hydroperoxide. The results are consistent with those obtained from electronic spectra.
An examination of the 13C NMR phenyl substituent effect in branched and non‐branched alkyl systems
Authors: Hearmon R. A.
Published: May 2005

Literature and unpublished data on alkylbenzenes have been analysed to give phenyl substituent effects. The effects have been determined for non‐α‐branched, α‐branched and α,α‐branched alkyl groups.
Structural studies of carbanionic species α to a phosphoryl group; anion from ketophosphonate comparison with related enoxysilanes and p‐ylid
Authors: Bottin‐Strzalko Tekla , Seyden‐Penne Jacqueline , Pouet Marie‐José , Simonnin Marie‐Paule
Published: May 2005

The structure of the carbanionic species 4 formed from diethyl(2‐oxopropyl)phosphonate and t‐BuOK has been studied by 1H, 13C and 31P NMR. In an associating medium (pyridine), a single chelated (C) carbanionic species 4Z (C) is observed. Two slowly interconverting species 4Z and 4E co‐exist when the anion‐cation interaction is loose, i.e. in Me2SO and when the gegenion K+ is complexed to (2,2,2)cryptand in Me2SO. The anionic carbon of 4Z and 4E is planar, and they have a strong enolate character as shown by the barrier to rotation around the C‐1C‐2 bond (ΔGc‡∼92 KJ mol−1). Their structures are compared to those of the related E and Z 1‐diethylphosphonato‐2‐trimethylsilyloxypropenes and to (acetylmethylene)triphenylphosphorane.
Carbon‐13 NMR investigation of some pharmacologically important cyclic n‐alkynylamines
Authors: Al‐Rawi Jasim M. A. , Behnam George Q. , Salman Salman R. , Muhi‐Eldeen Zuhair , Al‐Jawad Fuad H.
Published: May 2005

13C NMR spectra (22.63 MHz) of 23 cyclic amine derivatives of N‐alkynylphthalimides, N,N′;‐dialkynylpyromellitic acid diimides, N‐alkynyloxyphthalimides and 5‐p‐chlorophenyl‐2‐(4‐t‐amino‐2‐butynyl)thio‐1,3,4‐thiadiazoles were analysed. The influence on the 13C chemical shift of oxygen insertion between the nitrogen of the phthalimides and the methylene group was summarized.
Regio‐ and stereoselective alkylation of a pyrrolidinic system: Structural and conformational studies by high field NMR techniques
Authors: Schaefer M. , Faller P. , Nicole D.
Published: May 2005

A new merocyanine was prepared by addition of the pyrrolidine enamine of N‐ethoxycarbonylpyrrolidine‐3‐one to 1‐octyne‐3‐one. This addition was regioselective (with an unexpected C‐4 alkylation of the pyrrolidinone‐3‐enamine) and stereospecific (exclusively trans addition to the triple bond). The structure and conformational equilibrium were studied by high resolution proton magnetic resonance (NOE and variable temperature effects). Activation parameters ΔH*, ΔS* and ΔG* are given, and the behaviour on protonation examined.
Some calculations of solvent effects on one bond NC spin–spin couplings
Authors: Shargi S. N. , Webb G. A.
Published: May 2005

The solvaton model, incorporating INDO parameters and commonly encountered perturbation procedures, is employed to obtain the variation of 1J(N≡C) as a function of the dielectric of the medium (ϵ) for some cyanides and isocyanides. In all cases considered 1J(N≡C) is predicted to become increasingly negative as ϵ increases. Changes of up to 2 Hz in 1J(N≡C) are expected, with the isocyanides being more sensitive than the cyanides to a change in ϵ.
Ring distortion effect on δ13C values of bicyclo[4.n.0] alkanes
Authors: Metzger P. , Cabestaing C. , Casadevall E. , Casadevall A.
Published: May 2005

The 13C NMR spectra of trans‐ and cis‐fused bicyclo[4.n.0]alkanes, where n=4, 3 and 2, were determined. The distortion of the six membered ring, which is due to the strain arising from the 1,2 fusion of cyclohexane with a smaller ring, is apparent mainly for the chemical shifts of the ring junction carbons. Both for the trans‐and for the cis‐fused hydrocarbons the results support a cyclohexane in a chair conformation, distorted to a different degree according to the size of the other ring. The geometries of the different compounds in the series were calculated.
The use of Sn satellites in 1H NMR spectra of oriented molecules. The structure of phenyltin trichloride
Authors: Diehl P. , Amrein J.
Published: May 2005

The proton spectra of phenyltin trichloride including 119Sn‐ and 117Sn‐satellites have been analysed in isotropic and in oriented solvents. The indirect as well as the direct proton‐proton and proton‐tin coupling constants have been measured. From these the proton‐proton and proton‐tin internuclear distances corrected for harmonic vibrations have been derived.
1H NMR study of bacteriochlorophyll a radical anion: Use of difference spectra
Authors: Brereton Richard G. , Sanders Jeremy K. M.
Published: May 2005

The radical anion of bacteriochlorophyll a has been monitored by observing differential electron transfer broadening in the 1H NMR spectrum of diamagnetic bacteriochlorophyll in the presence of a small amount of chemically produced anion. The use of NMR difference spectra clearly indicates which sites in the anion have greatest spin density; these data are compared with other studies on the cation and anion.
Radical reactions in the co‐ordination sphere of transition metals. XIIIRadicals derived from 4,4′‐ and 2,2′‐Alkylidenebisphenolic Antioxidants
Authors: Omelka L. , Tkáč A. , Jiráčková L. , Pospíšil J.
Published: May 2005

Radical species were generated from 4,4′;‐ and 2,2′;‐alkylidenebisphenols during oxidation with free and co‐ordinated [Co(III)]RO2˙Radicals. This simulates the participation of bisphenolic antioxidants in the process of stabilization of hydrocarbons. Phenoxyls are primarily formed, and, depending on the character of the alkylidene bridge, some of them are gradually transformed into phenoxy radicals of the galvinoxyl type. Oxidation of alkylidenebisphenols by oxygen complexed to Co(II) yields co‐ordinated cyclohexadienonyloxy radicals. The character of the alkyl substituents on the phenolic nuclei specifically influences the stability of the generated phenoxy radicals at the applied temperature. The ESR characteristics of the primarily formed phenoxyls, phenoxyls of the galvinoxyl type and co‐ordinated cyclohexadienonyloxyls are discussed.
Carbon‐13 nuclear magnetic resonance studies on dichloropyridoquinolines
Authors: Molock Frank F. , Boykin David W.
Published: May 2005

Carbon‐13 NMR chemical shifts are reported for six angular and one linear dichloropyridoquinolines in CDCl3. The chemical shift assignments have been made using model compounds, fully coupled spectra, selective proton decoupling and results from lanthanide shift studies. Chlorine substituent effects are compared to those reported for chloroquinolines. The effect of the heteroaromatic nitrogen atoms on 13C1H coupling constants in these polycyclic systems are compared to those reported for pyridine systems.
NMR chemical shift substituent effects. 3—α‐Monosubstituted N,N‐diethylacetamides; bifunctional compounds in LSR experiments
Authors: Gutierrez Maria Alejandra , Martins Marcos A. P. , Rittner Roberto
Published: May 2005

Lanthanide‐induced shifts have been measured for some α‐heterosubstituted N,N‐diethylacetamides, using Eu(fod)3 in CCl4 solution. The resonances for the syn‐ and anti‐methylene and ‐methyl protons have been assigned unambiguously for some of these bifunctional amides. A simplified approach to the analysis of the geometry of the LSR–amide complexes is advanced, yielding average conformations which differ from the rotamers previously proposed. It demonstrates that the conformational equilibria are strongly perturbed by the lanthanide addition. The lanthanide was found to complex with the carbonyl oxygen atom lone‐pair in the less hindered position for some of the amides investigated, whereas the geometry of the complexes could not be determined for α‐(NN‐dimethyl)amino‐ and α‐methoxy‐N,N‐diethylacetamide. Mono‐ and bifunctional model compounds have also been measured to confirm the resonance assignments and the amide complexing site.
Conformational analysis of hydrazones.1H dynamic nuclear magnetic resonance and solvent effects in aryl‐ and 2‐furylaldehyde ethylaminoacetylhydrazones
Authors: Benassi Rois , Benedetti Adriano , Taddei Ferdinando , Cappelletti Roberto , Nardi Dante , Tajana Alberto
Published: May 2005

Aryl‐ and 2‐furylaldehyde ethylaminoacetylhydrazones were examined in different solvents and over a wide temperature range with1H NMR in order to study their conformational properties. Nearly equal amounts of theE/Zisomers, relative to the CN bond, are present, even when the solvents and the substituents on the aldimino carbon produce small changes in the isomeric mixture. The activation parameters of the thermal isomerization process were measured, and the results are in the line with a lateral‐shift type mechanism, also supported by theoretical calculations on a model compound. No other internal process was noted from the low‐temperature spectral behaviour, and this was interpreted in terms of a highly biased equilibrium concerning the rotation around the C(O)N bond. Chemical shifts obtained in different solvents also enable the most stable arrangement of the whole molecule of these compounds to be postulated.
Some INDO calculations of 1J(PN) values
Authors: Duangthai S. , Webb G. A.
Published: May 2005

Self consistent perturbation theory calculations of 1J(PN) are performed using INDO parameters. The change in sign of the coupling upon passing from tri‐ to penta‐valent phosphorus arises from the influence of the phosphorus lone‐pair electrons. The observed coupling trends are reproduced by the variation in the contact contribution which, in turn, depends largely upon the s character of the lone‐pair electrons on the coupled nuclei. There appears to be no significant role played by the phosphorus d orbitals in the couplings considered.
A proton NMR analysis of the OCH3 group conformation in 2‐methoxypyridines
Authors: Contreras R. H. , Facelli J. C. , de Kowalewski D. G.
Published: May 2005

The absence of HH couplings between the methoxy group and the ring protons observed in 2‐methoxy‐, 2,6‐dimethoxy‐ and 2‐methoxy‐6‐chloropyridines is interpreted in terms of a cis conformation between the methyl fragment and the nitrogen ring atom. Other data, taken from the current literature, support this conclusion.
Applications of 95Mo NMR. 5—substituent effects in the 95Mo and 13C NMR spectra of benzyltricarbonyl(η5‐cyclopentadienyl)molybdenum(II) derivatives
Authors: Brownlee R. T. C. , Masters A. F. , O'Connor M. J. , Wedd A. G. , Kimlin H. A. , Cotton J. D.
Published: May 2005

A systematic study has been made of the effects of substituent induced chemical shifts in [(η5‐C5H5)(CO)3Mo(CH2C6H4R)] compounds. Both 95Mo and 13C NMR shifts in the aromatic ring are reported. The (η5‐C5H5)(CO)3MoCH2 group is a reasonably strong resonance donor (σR° = −0.21) and weak inductive donor (σI = −0.07). The molybdenum chemical shifts are extremely sensitive to the effects of distant substituents (range c. 40 ppm). Since the shift correlates well with substituent constants in this series, it is suggested that the chemical shift is controlled by the paramagnetic term for this spin 5/2 nucleus.
13C NMR spectra of phosphole–P(IV) dimers; ABX and AA′X 13C31P coupling in some derived structures
Authors: Quin Louis D. , Mesch Keith A. , Bodalski Ryszard , Pietrusiewicz K. Michal
Published: May 2005

The easily obtained dimers of phosphole oxides, sulfides and methiodides give 13C NMR spectra where carbons within three (sometimes four) bonds of each 31P nucleus are doublets of doublets and thus constitute X in an AMX spectrum. Most of the spectra have been completely interpreted with the aid of spectral measurements at two magnetic fields. Saturation of the double bonds in dimers of methylphosphole–P(IV) derivatives causes the 31P nuclei to have very similar chemical shifts, with Δν not adequately different from 3J(PP) to give first‐order coupling. When both 31P nuclei couple with a given 13C, a second‐order (ABX) 31C NMR spectrum is obtained. The presence of the effect is revealed by running the 13C NMR spectra at high magnetic field; J(AX)+J(BX) is constant at all fields, but spacing between the lines of the multiplet varies. The spectrum of the oxide, with Δν/J=1.44 for the 31P spectrum at 36.43 MHz, approaches first order character at 75 MHz; the methiodide spectrum (Δν/J=4.55) is second order at 15 MHz but clearly first order at 50 MHz, and the sulfide (Δν/J=5.6) is nearly first order at 15 MHz. [2 + 2]‐Photochemical intramolecular cyclization of the dimer oxides provides cage‐like structures where the 31P nuclei are chemically equivalent, but magnetically non‐equivalent, making the 13C signals have the characteristics of X in an AA′X coupling pattern.
The structure of 2‐carboxyphenyl methyl selenoxide, its sodium salt and related compounds in solution, studied by 1H, 13C and 77Se NMR
Authors: Nakanishi Warö , Ikeda Yoshitsugu , Iwamura Hiizu
Published: May 2005

1H, 13C and 77Se NMR spectra of 2‐carboxyphenyl methyl selenoxides, 2‐carboxyphenyl phenyl selenoxides, their sodium salts and related compounds have been measured to determine their structures in solution. The 77Se NMR chemical shifts and the J(77Se, 13C) values were found to be particularly useful in distinguishing between selenuranes and selenoxides. The downfield shifts of 286‐536 and 587‐667 ppm from selenoanisoles are characteristic of the corresponding selenuranes and selenoxides, respectively. The couplings were 61‐65 and 77‐81 Hz for the selenuranes and selenoxides, respectively. The effects of salt formation on the NMR parameters are also discussed. The results show that the carboxylic acids have the cyclic selenurane structure, whereas the salts are acyclic selenoxides.
cis–trans isomerization of 2‐(4‐pyridyl)‐substituted thiazolidine‐4‐carboxylic acids: pH dependence by 1H and 13C NMR
Authors: Ponticelli Fabio , Marinello Enrico , Missale Maria Cristina
Published: May 2005

The presence of two diastereoisomeric thiazolidines obtained by the reaction of L‐cysteine or L‐cysteine ethyl ester and pyridoxal or pyridoxal‐5‐phosphate is demonstrated by 1H and 13CNMR spectroscopy. Fast interconversion of isomers occurs in neutral or alkaline solution.
Carbon‐13 NMR study of isoxazolopyridine systems
Authors: Chimichi Stefano , Tedeschi Piero , Camparini Alfredo , Ponticelli Fabio
Published: May 2005

The 13C NMR spectra of all azabenzenoid isoxazolopyridines and some of their chloro derivatives are discussed. All 13C resonances were unambiguously assigned by means of gated decoupled spectra, from which one‐bond and long‐range 13C1H coupling constants have been determined from line splittings.
Radical reactions in the co‐ordinated sphere of transition metals. XIV—spin distribution of phenoxy radicals generated from biphenyldiols
Authors: Pelikán P. , Tkáč A. , Omelka L. , Staško A.
Published: May 2005

The phenoxy radicals obtained from 2,2′‐ and 4,4′‐biphenyldiols show, in nonpolar solvents, symmetrization of the unpaired electron spin density on the two phenyl rings in the temperature range 290–410 K. Below 270 K the paramagnetic systems became diamagnetic. This para‐diamagnetic conversion with temperature is reversible. According to INDO calculations the symmetrization of spin density is due to the formation of dimeric phenoxy radicals. The para‐diamagnetic conversion at various temperatures is explained by the reversible conversion of the radical dimer to the quinone‐hydroquinone pair.
Calculations of some 1J(SiC) and 1J(SiF) values
Authors: Duangthai S. , Webb G. A.
Published: May 2005

Some calculations of 1J(SiC) and 1J(SiF) are performed by self‐consistent perturbation theory employing standard INDO parameters. 1J(SiC) is dominated by the contact interaction, whereas the opposite sign for 1J(SiF) is due to a large orbital interaction. The 1J(SiC) data are satisfactorily reproduced by calculations employing an sp basis set, whereas the inclusion of silicon 3d orbitals provides a more reasonable account of 1J(SiF).
Compounds with bridgehead nitrogen: 45—the 1H NMR spectra and stereochemistry of some dimethylperhydro‐oxazolo[3,4‐a]pyridines
Authors: Crabb Trevor A. , Heywood Geoffrey C.
Published: May 2005

The positions of conformational equilibria in 1,5‐, 1‐6‐ and 1,8‐dimethylperhydro‐oxazolo[3,4‐a]pyridines were determined by 1H NMR spectroscopy. The cis‐(H‐5, H‐8a)‐1,6‐dimethyl‐perhydro‐oxazolo[3,4‐a]pyridine. In contrast, r‐1,t‐6,t‐8a‐1,6‐dimethylperhydro‐oxazolo[3,4‐ a]pyridine preferred the cis‐fused conformation. Three of the 1,8‐dimethylperhydro‐oxazolo[3,4‐a]pyridines adopted the trans‐fused conformations (with distortion of the system in the case of the r‐1,c‐8,c‐8a derivative) and the r‐1,c‐8,t‐8a‐1,8‐dimethyl derivative adopted the cis‐fused conformation.
Stereochemical studies of substituted 6,7‐ benzomorphan derivatives by 13C and 1H NMR spectroscopy
Authors: Casy A. F. , Ogundaini A. O. , Parfitt R. T.
Published: May 2005

The 13C NMR spectra of a series of 6,7‐benzomorphan derivatives variously substituted at C‐5 and C‐9 by methyl and at C‐3 by cyano, alkyl and aralkyl groups, together with certain 3‐cyano, 3‐allyl or benzyl congeners, are reported and chemical shift data analysed in terms of the configuration of isomeric pairs and compounds isolated as single diastereoisomers. Special attention is given to the consequences of γ‐shielding interactions, the effects of the nitrogen lone‐pair orbital and anisotropic shielding by the aromatic region of the molecule. Deductions of stereochemistry are supported by 1H NMR data and the NMR features of the corresponding methiodide salts.
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

2D 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

The 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

Some 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

The 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

The 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

Values 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

Studies 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

Carbon‐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

Long‐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

The 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

The 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

On 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

13C 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

Proton 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

Monopropiophenone 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

The 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

Oxazolidine 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.
Oxygen‐17 NMR chemical shifts of esters
Authors: Orsini Fulvia , Ricca Giuliana Severini
Published: May 2005

The 17O NMR spectra of some esters are discussed and are correlated with 13C NMR chemical shift and IR carbonyl streching band data.
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

13C 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

The 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

The 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

Carbon‐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

Carbon‐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

The 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

The 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.