bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of 2‐pyrrolidone, δ‐valerolactam and ϵ‐caprolactam: Nuclear magnetic relaxation of carbon‐13 and nitrogen‐15
Authors: Marchal J. P. , Brondeau J. , Canet D.
Published: May 2005

The molecular dynamics and the association of 2‐pyrrolidone, δ‐valerolactam and ϵ‐caprolactam in H2O and CCI4 solutions have been investigated by 13C nuclear magnetic relaxation. With the aim of unambiguously establishing 13C assignments the following parameters have been measured: carbon chemical shifts, one‐bond carbon–proton coupling constants and one bond carbon–carbon coupling constants. In the particular case of 2‐pyrrolidone, the 13C relaxation times do not provide enough information in order to study in detail the dynamics of the molecule. 15N Relaxation for the neat liquid has proved to be a valuable complement for totally analysing the anisotropic motion of this lactam.
Hydrolysis of γ‐[1‐methyl‐5‐bis(β‐chloroethyl) amino‐2‐benzimidazolyl]butyric acid. Studied by 1H NMR
Authors: Klose G. , Augsten K. , Barth A. , Samek Z.
Published: May 2005

High resolution 1H NMR is applied to the study of hydrolysis and equilibria in the complex system of γ‐[1‐methyl‐5‐bis(β‐chloroethyl)amino‐2‐benzimidazolyl]butyric acid and D2O. Kinetic data for the individual hydrolytic steps are obtained for the first time. The hydrolytic reactions are pseudo first order. The differences in the activation energies of the two hydrolysis steps are accounted for by different intermediates. Furthermore, equilibrium constants for the deuteration of the N mustard group in the individual products are quantitatively estimated. They show an increase of the basicity of N mustard with hydrolysis. The applicability of the 1H NMR method is restricted to a pD range of 0.5–4.
Computer supported structure elucidation of polymethoxy‐ and polyacetoxyxanthones. V—13C NMR spectroscopy of substituted xanthones
Authors: Frahm A. W. , Hambloch H.
Published: May 2005

A procedure for developing 13C NMR chemical shift additivity rules for all 136 polymethoxyxanthones and all 136 polyacetoxyxanthones, based on multiple linear regression analysis, is reported. The influence of steric interactions between the substituents on the chemical shifts of the carbon atoms in the xanthone ring system is discussed and included in the calculations of the additivity rules for the polymethoxyxanthones. The derived chemical shift increments are implemented into the computer program SEOX 1. The extended program, SEOX 2, allows an automated structure elucidation of polyhydroxy‐, polymethoxy‐ and polyacet‐oxyxanthones. The increments are tested using the leave‐one‐out method in conjunction with SEOX 2, and have been found to be very suitable for this purpose.
1H NMR spectra of substituted phenazines
Authors: Römer Axel
Published: May 2005

The 1H NMR Spectra of 28 substituted phenazines have been measured and analysed with computer assistance. Substituent increments of chemical shifts were calculated for methoxy, carbomethoxy and methyl derivatives. The influence of these substituents on coupling constants has been examined.
13C and 77Se NMR spectra of thienoisoselenazoles, selenoloisothiazoles, selenoloisoselenazoles and thienoisothiazoles
Authors: Onyamboko N. V. , Renson M. , Chapelle S. , Granger P.
Published: May 2005

The 13C and 77Se NMR spectra of eight new unsubstituted biheterocycles containing a thiophene or selenophene ring condensed with an isothiazole or isoselenazole ring were recorded. The assignments of the 13C signals were made by the examination of chemical shifts, 1J(CH) coupling constants and, for the quaternary carbons, on the basis of 1J(C, 77Se) coupling constants. The results are compared and discussed.
Oxygen‐18 isotope effects on 13C NMR signals
Authors: Everett Jeremy R.
Published: May 2005

A survey of 18O isotope effects on 13C chemical shifts shows that a linear relationship exists between the magnitude of the one‐bond isotope effect and the chemical shift of the carbon atom for carbonyl groups. No such correlation was found for functional groups in which the oxygen atoms are connected to the carbon atoms via single bonds.
13C NMR of organosulfur compounds the 13C chemical shifts of monocyclic γ‐ and δ‐sultones
Authors: Smith Michael B. , Wolinsky Joseph
Published: May 2005

The 13C NMR spectra of several monocyclic γ‐sultones(1,2‐oxathiolane 2,2‐dioxides) and δ‐sultones(1,2‐oxathiane 2,2‐dioxides) have been determined and are presented herein. The chemical shifts of the ring carbons of these compounds are compared in terms of conformational, electronic and anisotropic differences. Electric field effects may be responsible for the chemical shifts of the C‐α carbon, but do not appear to be important for C‐α. Anisotropic deshielding also appears to be important for the chemical shifts of C‐α, but the effects on C‐α appear to be small. Dipole changes at C‐α and C‐α, induced by back donation of electron density from the ring oxygen to sulfur, may explain the chemical shifts at C‐α. Substituent effects are readily explained in terms of well‐known effects. In general, the carbons closest to the sulfonate group are found to be the most affected, and the carbons of the δ‐sultones proximate to the sulfonate group are found to be more deshielded than those of the γ‐sultones.
13C relaxation times, T1, in six‐coordinate cobalt(III) complexes: Study of the axial CoN (heterocyclic) bond
Authors: Huet Jack , Gaudemer A.
Published: May 2005

Carbon‐13 relaxation times, T1, have been measured for ten cobalt(III)–cyclohexanedione dioxime complexes: CH3CH2Co(Niox)2‐p‐R‐pyridine [RH, N(CH3)2, CH3, C2H5, C(CH3)3, Cl, Br, CN and COCH3] and CH3CH2Co(Niox)2‐3‐N‐methylimidazole. The values obtained have been rationalized by making assumptions on the length of the metal—hetrocyclic nitrogen bond. The internal rotation around the axial CoN (heterocyclic) bond is faster for the 3‐N‐methylimidazole ligand than for the pyridine ligands. Correlations of the T1 values with the σ‐donor and π‐acceptor character of the pyridine ligands were attempted. The interpretation of the results suggests the existence of π‐back‐bonding from the metal to the N‐1 pyridine nitrogen atom, in agreement with the results of other workers. This conclusion, however, was not supported by the use of the para‐C chemical shift as a criterion for back‐bonding in pyridine–transition metal complexes.
13C NMR spectra of benzo[b]thiophene and 1‐(X‐benzo[b]thienyl)ethyl acetate derivatives
Authors: Al‐Showiman Salim S. , Al‐Najjar Ibrahim M. , Amin Hassan B.
Published: May 2005

Carbon‐13 chemical shift assignments are reported for benzo[b]thiophene and 1‐(X‐benzo[b]thienyl)ethyl acetate derivatives, where X=CH(OAc)CH3 substituted at positions 2‐7. Substituent chemical shift (SCS) effects for the ethyl acetate group are additive at all positions. A substantial upfield shift was observed at C‐3, arising from the peri interaction of H‐3 and the 4‐ethyl acetate substituent. Carbon‐13 relaxation times (T1) and nuclear Overhauser enhancements (η) have been measured for benzo[b]thiophene and its derivatives, and the contributions of dipolar, TDD1, and spin rotation, TSR1, relaxation have been determined. Intramolecular dipole–dipole interactions are found to provide by far the most important spin‐lattice relaxation mechanism whenever protons are bound directly to the carbons under investigation. Nonprotonated ring carbons are relaxed by both DD and SR mechanisms. Anisotropic motion has an easily observable effect on the DD contribution to T1, and can form the basis for spectral assignments, as in 1‐phenylethyl acetate. Long‐range 13C1H coupling constants were observed both between ring carbons and between ring carbons with ring side‐chain hydrogens. These results have been used for the structure determination of the title compounds.
Carbon‐13 nuclear magnetic resonance spectra of exo‐ and endo‐2‐norbornyltrimethyl‐stannanes: Corrected assignments
Authors: Kitching William
Published: May 2005

The 13C NMR spectra of pure exo‐2‐norbornyltrimethylstannane and a mixture of the exo‐ and endo‐isomers have been recorded. 1H–13C polarization transfer spectra have been obtained and require the previously reported assignments for C‐3 and C‐4 in the exo‐isomer to be reversed. The reported assignments for the endo‐isomer are correct. The new assignment for C‐4‐exo [with J(119Sn,13C) vic=12 Hz, instead of the previously assigned J(vic)=23 Hz], has a very minor effect on the nature of the Karplus curve [for 3J(119Sn,13C)] generated previously.
Application of NMR spectroscopy of chiral association complexes. 13—electron donor–acceptor complexes between racemic carbazolo[3,4‐c]carbazoles and an optically active acceptor
Authors: İçli Siddik , Burgemeister Thomas , Mannschreck Albrecht , Zander Maximilian
Published: May 2005

Strong electron donor–acceptor (EDA) association between carbazolo[3,4‐c]carbazoles and an optically active tetranitrofluorenone derivative was detected by UV–visible spectroscopy and by 1H NMR shifts. 1H NMR splittings at low temperatures are due to diastereomeric association complexes and, thus, prove the chirality of carbazolocarbazoles.
Electron spin resonance studies of several anion radicals of nitro‐substituted thioacylpiperidines and morpholines
Authors: Cercasov C. , Cornea F. , Ciureanu M. , Hillebrand M. , Sahini V. E. , Volanschi E.
Published: May 2005

The radical anions of m‐ and p‐ nitro‐substituted derivatives of several classes of N‐(thioacyl)‐piperidines and ‐morpholines have been studied by ESR spectroscopy. The anion radicals were found to be centred on the nitro group, and the distribution of the unpaired electron was found to be dependent on the extent of conjugation between the thiocarbonyl group and the aromatic moiety of the molecule. The hfs constants were discussed in terms of the spin densities calculated by the McLachlan procedure.
13C NMR studies of some complex natural oxygen heterocycles. V—13C NMR spectra of furanoflavones
Authors: Gupta S. C. , Singh F. P. , Cook I. B. , Ternai B.
Published: May 2005

13C NMR spectra for a number of furanoflavones are presented and analysed. The effects of various substituents are discussed.
Structural studies on 6‐methyl‐9‐carbamoyl‐tetrahydro‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones by 1H, 13C and 15N NMR spectroscopy
Authors: Tóth Gábor , de La Cruz Carlos , Bitter István , Hermecz István , Pete Béla , Mészáros Zoltán
Published: May 2005

Several 6‐methyl‐9‐carbamoyltetrahydro‐4H‐pyrido[1,2‐α]pyrimidin‐4‐ones have been prepared using phosgene iminium chloride. These compounds can exist in equilibrium as the cis (3A) imine ⇌ (3B) enamine ⇌ trans (3C) imine. 1H, 13C and 15N NMR prove that the cis‐ and trans‐imine isomers are predominant in the equilibrium. 1H NMR data reveal that the share of the 3B enamine form is negligible at measurable concentrations. The isomeric ratio 3A:3C is time dependent and can be monitored by measuring the CH3C‐6 and (CH3)2N signals. The 13C NMR data show that doublets in the range 42–45 ppm for C‐9 are only compatible with the imine forms 3A and 3C. The SCS values of the CH3C‐6 and OCN(CH3)2 groups were calculated and used for identification of the cis and trans isomers. 15N NMR data show that the N‐1 chemical shift of the imine is approximately − 140 ppm for compound 3, whereas that of a fixed enamine is around − 267.8. This provides additional support for the predominance of the imine tautomers in the equilibrium 3A ⇌ 3B ⇌ 3C. 15N data allow the stereoisomers 3A and 3C to be distinguished.
Barriers to rotation of the dimethylamino group in some 2‐amino‐4‐(N,N‐dimethylamino)pyrimidines
Authors: Wells C. H. J.
Published: May 2005

The free energy of activation for rotation about the exocyclic CN bond of the dimethylamino group of some 6‐substituted 2‐amino‐4‐(N,N‐dimethylamino)pyrmidines has been determined using 1H NMR line shape analysis. The results are discussed in terms of the relative electron‐withdrawing and electron‐releasing effects of the substituents.
Carbon‐13 NMR of quinone methides
Authors: Benson Mabry , Jurd Leonard
Published: May 2005

The 13C NMR spectra of four ortho‐ and seven para‐quinone methides were assigned using chemical shift and long‐range carbon‐proton coupling information. The carbonyl shifts are compared with those in ortho‐ and para‐benzoquinones. The chemical shifts of the carbonyls of the p‐quinone methides are observed at δ 186.2–186.4 for the three ortho‐di‐tert‐butyl‐substituted compounds and at δ 180.7–181.5 for the four ortho‐oxy‐substituted compounds. In the three o‐quinone methides with meta, para‐dioxy substituents, the carbonyl signals are at δ 184.2–185.4. The carbonyl signal of the one o‐quinone methide with no oxygen substitution is shifted downfield to δ 200.9, apparently as a result of hydrogen bonding to the nearby hydroxyl.
Application of biosynthetic 13C‐enrichment using [1‐13C]‐, [2‐13C]‐ and [1,2‐13C2]‐acetate as precursor for 13C NMR spectral assignment of higher plant metabolites. The assignments of some bryonolic acid derivatives
Authors: Kamisako Wasuke , Suwa Kiyoko , Morimoto Kayoko , Isoi Koichiro
Published: May 2005

The 13C NMR spectra of some derivatives of bryonolic acid (1) (D:C‐friedoolean‐8‐en‐3β‐ol‐29‐oic acid) were assigned by means of 13C‐enrichment, lanthanide‐induced shifts (LIS) and comparison of chemical shift data between derivatives. The 13C‐enriched species of 1, i.e., 1a, 1b and 1c were biosynthesized by Luffa cylindrica (Cucurbitaceae) callus fed with [1‐13C]‐, [2‐13C]‐ or [1,2‐13C2]‐acetate, respectively. Methyl acetylbryonolates 2, 2a, 2b and 2c, methyl bryonolates 3, 3a, 3b and 3c, methyl bryononates 4 and 4a, diacetyl‐3β,29‐diols (3,29‐diacetyl‐D:C‐friedoolean‐8‐en‐β,29‐diol) 5, 5a, 5b and 5c, and 3‐acetyl‐3β,29‐diols 6, 6a and 6b were prepared from 1, 1a, 1b and 1c, and their 13C NMR spectra were recorded. The 13C concentration of the 13C‐enriched species was high enough to exhibit the satellite peaks clearly, and the analysed data were very useful for this study. Thus, total assignments for 2, 3, 4, 5 and 6 were established. It was found that conversion of the methoxycarbonyl group at C‐29 into an acetoxymethyl group caused complex changes in the chemical shifts of the C, D‐ and E‐ring carbons and those of the methyl carbons linked to these rings.
1H NMR study of naphthoflavones with shift reagents
Authors: Joseph‐Nathan P. , Santillan R. L.
Published: May 2005

The complete assignment of the proton NMR spectra of several α‐, β‐ and γ‐ naphthoflavones at 100 MHz using Eu(fod), and double resonance experi‐ ments has been carried out. The compounds were found to associate at the carbonyi oxygen, by analogy with flavones where complete structural assignment can be attained using Pr(fod)3, at 60MHz. The three types of naphthoflavones can be distinguished by observation of the quantitative lanth‐ anide‐induced shifts at H‐3 and/or H‐5, combined with their chemical shift values in the absence of shift reagent.
Methyl carbon chemical shifts of methylbenzoic acids and methylbenzoate anions
Authors: Guilleme Joaquin , Diez Ernesto , Garrigos Lluis , Esteban Angel L.
Published: May 2005

Methyl carbon chemical shifts have been assigned for methylbenzoic acids dissolved in CDCl3, and for methylbenzoate anions obtained by dissolving these acids in aqueous NaOH solution. Chemical shifts have been interpreted by means of additive substituent parameters which reflect conformational features existing between adjacent substituents. Barriers to rotation of a methyl group adjacent to a carboxyl or carboxylate group have been estimated to differ by less than 2 kJ mol−1 from the barrier of a methyl group in o‐xylene.
Carbon–proton coupling constants in allenes, ethenes and butatrienes. Application to conformational analysis of allenyl and vinyl alkyl ethers and thioethers
Authors: Koole N. J. , de Bie M. J. A. , Hansen P. E.
Published: May 2005

Experimental carbon–proton coupling constants are reported for 36 monosubstituted allenes, 20 ethenes and 5 butatrienes. The data for the allenes cover a range of substituents in which either the first atom of the substituent (all Group IV–VII elements of the second and third row are covered) and/or the substitution of that atom is varied. The electronegativity (σI) of the substituent directly attached to the coupled carbon atom is correlated with the 1J(CH) coupling. This is also borne out by the good correlations between 1J(CH) values in the allenes and 1J(CH) values in various other classes of chemical compounds. Theoretically calculated 1J(CH) values correctly reflect the substituent effects on the experimental values in the allenes, ethenes and butatrienes spearately, but fail to give a satisfactory description of the differences in 1J(CH) for these types of compounds. In disubstituted allens and ethenes the substituent effects on 1J(CH) values are additive. The experimental and calculated values differ by less than 1 Hz. Two‐ and three‐bond carbon–proton couplings are also discussed in terms of electronegativity, substituent and hybridization effects and mutual relationships. Large values, up to 6 Hz, are found for 4J(CH) and 5J(CH) in the allenes and butatrienes. These large values are ascribed to σ‐π interactions. For geometrically equivalent couplings a constant ratio of nJ(CH)/nJ(HH) is found in the ethenes (0.65; n = 3) and in the allenes and butatrienes (0.55; n = 4 and 5, respectively). 1J(CH) and 3J(CH) coupling constants are used for the conformational analyses of vinyl, allenyl and butatrienyl ethers and thioethers. At room temperature the methyl and ethyl ethers are predominantly in an s‐cis conformation, whereas the iso‐propyl allenyl ether is a mixture of s‐cis and s‐trans; the tert‐butyl allenyl ether exists mainly in the s‐trans conformation. The thioethers are all in the s‐cis conformation.
Dimers from cyclic α‐diketones. Confirmation of structure by solid‐phase CPMAS 13C NMR spectroscopy
Authors: Macomber Roger S. , Murphy Paul
Published: May 2005

The solid‐phase 13C CPMAS NMR spectra of the crystalline dimers from 10‐, 12‐ and 14‐membered cyclic α‐diketones were found to be in full accord with the symmetrical tricyclic 2,5‐dihydroxycyclohexane‐1,4‐dione structures previously proposed on the basis of molecular formulae and infrared spectroscopy.
Carbon‐13 spin–lattice relaxation of tropane alkaloids. Anisotropic rotational motion of tropine and pseudotropine
Authors: Uusvuori Raimo , Lounasmaa Mauri
Published: May 2005

The 13C spin–lattice relaxation times of tropine and pseudotropine have been measured in CDCl3 as a function of concentration. The same relative increase in concentration serves to increase the relaxation rates much less in the region 0.9–5.0 wt.% than in the region 5.0–14.3 wt.%. The rotational diffusion coefficients have been calculated from the relaxation data using Woessner's anisotropic rotational diffusion model. Reorientation of both molecules is shown to be moderately anisotropic. The principal axes of the rotational diffusion tensor in the symmetry plane of both molecules are rotationally shifted from the principal axes of the moment of inertia tensor of the free molecules, and the main rotational axis is parallel with a line passing through the centre of mass of the molecule and the nitrogen atom.
Carbon‐13 NMR of some organophosphorus compounds. 2—chemical shifts and PC coupling constants of diaryl‐, dialkoxy‐ and diaryloxy‐phosphine amines with general formula Y2PNRR'
Authors: Al‐Rawi Jasim M. A. , Sheat M. A. , Ayed Nacur
Published: May 2005

Carbon‐13 chemical shifts and 2J(POC), 3J(POCC), 2J(PNC) and 3J(PNC) coupling constants of 30 compounds containing the amine moiety, with the general formula Y2PNRR' (Y  C6H5, CH3O, CH3CH2O, CH2O; Y2  1,2‐dioxybenzene) have been determined. J(PNC) values have been used to explain the preferred conformation around the PN bond. A comparison between 2J(PNC) and 2J(PNH) was accomplished.
Carbon‐13 NMR spectroscopy of some Strychnos alkaloids. Part 2
Authors: Verpoorte R. , van Beek T. A. , Riegman R. L. M. , Hylands P. J. , Bisset N. G.
Published: May 2005

13C NMR data for a series of natural and semi‐synthetic ar‐hydroxy‐ and ‐methoxy‐substituted Strychnos alkaloids are presented and are used to determine substituent‐induced chemical shift (SCS) values for the various substitution patterns.
13C NMR spectroscopic study of lupinine and epilupinine salts and amine oxides
Authors: Podkowinska Halina , Skolik Jerzy
Published: May 2005

The 13C NMR spectra of the isomeric alkaloids lupinine and epilupinine and their perchlorates, methiodides and N‐oxides are discussed. Chemical shift changes due to protonation, quaternization and N‐oxidation are analysed. The trans‐quinolizidine ring fusion is proved for epilupinine salts and for the N‐oxide. Lupinine also exists predominantly with the trans ring fusion, but the cis ring fusion is found in the methiodide. An equilibrium of two stereoisomers, one with trans‐ and the other with cis‐ring fusion, has been established for lupinine perchlorate in D2O solution. Lupinine N‐oxides isolated in the crystalline state are shown to have both trans‐ and the cis‐ring fusion.
Conformation of a diastereoisomeric pair of enkephalin analogues: A 400 MHz 1H NMR study
Authors: Bajusz S. , Casy A. F.
Published: May 2005

1H NMR spectra recorded at 400 MHz of the enkephalin analogues Tyr‐D‐NIe‐Gly‐Phe‐D(and L)‐NIeS and the dipeptide Ac‐Phe‐D‐NIeS as solutes in DMSO‐d6 are reported and assigned. A preferred conformation of the D2L5 peptide is proposed, based on evidence of an intramolecular hydrogen bond between Phe4 NH and Tyr1 CO and NH/a‐CH coupling constants. The possibility of conformational differences between the isomeric peptides accounting for differences in their ability to bind to δ‐opiate receptors is discussed.
1H NMR separation of epimeric mixtures by lanthanide shift reagents: Analysis of some isoxazolidine derivatives
Authors: Bucci P. , Chidichimo G. , Liguori A. , Menniti G. , Uccella N.
Published: May 2005

Epimeric mixtures of isoxazolidine derivatives were investigated by 1H NMR spectra obtained in the presence of lanthanide shift reagents. The NMR signals of all the components contained in a mixture of 2,3‐diphenyl‐5‐carboxymethylisoxazolidines were identified and the LISCA computer program enabled the stereochemistry of the different isomers to be established.
The study of longifolene by two‐dimensional NMR spectroscopy
Authors: Joseph‐Nathan P. , Santillan R. L. , Schmitt P. , Günther H.
Published: May 2005

The complete assignment of the 13C NMR spectrum of longifolene was achieved from double quantum coherence measurements, while combined evaluation of a 1H13C heteronuclear chemical shift correlation diagram and a homonuclear 1H J‐resolved diagram provided all proton chemical shifts. Conformational information on the seven‐membered ring of the tricyclic sesquiterpene was obtained from proton chemical shift considerations.
A 13C NMR study of β‐carboline alkaloids
Authors: Koike Kazuo , Sakamoto Yohko , Ohmoto Taichi
Published: May 2005

The 13C NMR spectra of β‐carboline alkaloids were determined, and unambiguous assignments of the spectra were carried out from the long‐range coupling constants.
Selenium‐77 NMR chemical shifts of five‐membered selenium and sulphur heterocycles with CSe, CS, and CO groups
Authors: Poleschner Helmut , Radeglia Reiner , Meyer Hinrich
Published: May 2005

This paper reports the 77Se NMR chemical shifts of 1,3‐dithiole‐, 1,3‐thiaselenole‐ and 1,3‐diselenole‐2‐ones, ‐thiones and ‐selones, of the corresponding saturated compounds 1,3‐diselenolane‐2‐one, ‐thione and ‐selone, and the 1,3‐thiaselenolium tetrafluoroborates, either unsubstituted or substituted by morpholino, ethylthio or ethylseleno groups in the 2‐position. The 77Se chemical shift values of the ring selenium and the CSe groups are compared with the 13C chemical shift values of neighbouring carbon atoms. The relationships between the 77Se chemical shifts of the CSe groups and the wavelengths of their n→* absorption in the UV‐visible spectrum are discussed with respect to the significance of the δE term in the contribution of the paramagnetic screening and the electron density distribution.
13C NMR spectroscopic evidence for the existence of the monocation of pyropheophytin a
Authors: Lötjönen Simo , Hynninen Paavo H.
Published: May 2005

Pyropheophytin a, which is an unsymmetric porphyrin, has been titrated with trifluoroacetic acid (TFA) in tetrahydrofuran, the protonation reaction being followed by 13C NMR spectroscopy. TFA was added in small increments to a 0.28 M solution of pyropheophytin a in tetrahydrofuran, and the chemical shift changes of the macrocyclic carbons were determined as a function of the TFA increments. On the addition of TFA the signals of the α‐carbons of ring II experienced a large upfield change, whereas the signals of all other macrocyclic carbons moved only slightly downfield or remained constant. These observations were interpreted as indicating the formation of a monocation in which the proton is attached to the nitrogen of ring II. The 13C protonation shifts of pyropheophytin a were compared with those previously reported for symmetric porphyrins. On the basis of this comparison, the basicity of the macrocyclic nitrogen atoms, the N–H tautomerism and the electron delocalization in structurally different porphyrin macrocycles are discussed.
Conformation changes induced in 2‐spiro‐substituted cephalosporin sulphoxides by the configuration of the spiro bond: A combined 1H and 13C NMR study
Authors: Erdödiné‐Kövér Katalin , Jászberényi J. Cs.
Published: May 2005

1,3‐Dipolar cycloadditions of diazomethane and diphenyldiazomethane to exo‐2‐methylenecephalosporins are described. A structural study of the products shows that the initially formed 2‐spiropyrazolinocephems form cyclopropanes by the spontaneous loss of nitrogen. ASIS and NOE measurements reveal that the products with different C‐2 configurations are in two different conformations.
13C NMR chemical shifts of N‐unsubstituted‐ and N‐methyl‐pyrazole derivatives
Authors: Cabildo Pilar , Claramunt Rosa Maria , Elguero Jose
Published: May 2005

13C shielding data for 100 derivatives of pyrazole are reported. These include methyl, ethyl, n‐propyl, tert‐butyl, phenyl, hydroxymethyl, carboxyl, ethoxycarbonyl, cyano, amino, hydrazino, nitro, azido, chloro, bromo and iodo groups as substituents on the ring carbon atoms.
The solvent effect on the isotropic hyperfine interaction in some aliphatic polyamine copper(II) complexes
Authors: Pisipati V. G. K. M. , Rao N. V. S. , Muralikrishna V. , Murthy V. S. , Kesavan T.
Published: May 2005

ESR and optical absorption studies are described for a number of copper(II) chelates with aliphatic polyamines, exhibiting both square pyramidal and square bipyramidal coordination around the copper ion. The complexes studied were bis(N,N′‐dimethylethylenediamine)copper(II) sulphate tetrahydrate, bis(N,N′‐diethylethylenediamine)copper(II) nitrate, diaquosulphato(N,N,N′,N′‐tetramethylethylenediamine)copper(II) hydrate, dinitrato(N,N,N′,N′‐tetramethylethylenediamine)copper(II), dichloro(N,N,N′,N′‐tetramethylethylenediamine)copper(II) and dithiocyanato(N,N,N′,N′‐tetramethylethylenediamine)copper(II). The ESR measurements were carried out in methanol, dimethyl sulphoxide, dimethylformamide and pyridine, at room and liquid nitrogen temperatures. The molecular orbital coefficients were estimated assuming an axial symmetry. The parameter χ proportional to the hyperfine constants shows a variation with the solvent for all these complexes. The χ values in solution are lower than the corresponding average χ values reported in the solid state for each complex. The solvent effect and the influence of 4s character in the ground state are discussed. The χ values, either calculated or reported, for a number of copper complexes for [4O], [3O, N], [2O, 2N], [O, 3N] and [4N] environments around copper(II) are presented.
Study of the formation of copper phthalocyanine by EPR spectroscopy
Authors: Döscher Burghard , Priess Renate , Gunsser Walter
Published: May 2005

The mechanism of the formation of copper phthalocyanine in the phthalic anhydride/urea process was elucidated by employing 14N, 15N or mixed nitrogen donors and enriched 63Cu for the synthesis of the pigment. Both EPR spectroscopy of the magnetically dilute complex and IR spectroscopy of oxidative fission products provide information about the isotopic composition of the inner chelate sphere. The range of superhyperfine interaction detectable by the EPR method was analysed by means of copper phthalocyanine labelled with 13C at positions 1, 4, 6, 9, 11, 14, 16 and 19. The results confirm a reaction mechanism which includes the formation of phthalonitrile as an intermediate product.
13C NMR studies of methylnucleosides
Authors: Chang Ching‐jer , Ashworth Dennis J. , Chern Lih‐Ju , Gomes Jose DaSilva , Lee Chi‐Gen , Mou Pih W. , Narayan Ramani
Published: May 2005

The 13C chemical shifts of 22 methylated ribonucleosides and deoxyribonucleosides have been measured and assigned. The chemical shift differences between methylated and unmodified nucleosides are correlated with their characteristic modifications of structure. The significance of the chemical shift and tautomeric variations is discussed.
Additive chemical shift parameters for methylene protons. Shoolery's constants reinvestigated
Authors: Bell Harold M. , Berry Linda K. , Madigan Elizabeth A.
Published: May 2005

Methylene proton chemical shifts have been studied using multiple linear regression analysis, and additive chemical shift parameters have been determined. Using a data set of 1007 chemical shifts, involving 48 different substituents, a standard error of estimate of 0.15 ppm was found for protons spread between 2.0 and 5.9 ppm. Provision was made in the data matrix for substituent effects for directly attached groups (α) and for groups attached via one intervening saturated carbon (β‐substituents). The influence of groups more remotely located was assumed to be negligible. Although the parameters were optimized for deshielded methylene proton shifts, they also serve satisfactorily for the estimation of shifts in more shielded methylene cases.
13C and 77Se NMR of some organometallic derivatives with Ti, Zr and Hf
Authors: Granger P. , Gautheron B. , Tainturier G. , Pouly S.
Published: May 2005

13C and 77Se NMR was carried out on dicyclopentadienyl derivatives of Ti, Zr and Hf with selenium bonded directly to the metal. Although 13C NMR is not sensitive to different substitution, 77Se NMR is valuable and reflects the influence of the different organic substituents and the nature of the metals bonded to the selenium atom.
Oxygen‐17 nuclear magnetic resonance spectral investigation of 3‐alkoxy‐trans‐3,4‐disubstituted‐thiolane 1,1‐dioxides and related compounds
Authors: Sammakia Tarek H. , Harris David L. , Evans Slayton A.
Published: May 2005

The 17O NMR spectra of 3‐alkoxythiolane 1,1‐dioxides indicate that the sulfonyl oxygens are diastereotopic but their chemical shift differences are essentially independent of the structure of the alkyl group in the alkoxy moiety. Eu(fod)3 enhances the 17O chemical shift differences between the diastereotopic sulfonyl oxygens in 3‐isopropoxythiolane 1,1‐dioxide and shifts both oxygens upfield. α,β‐Unsaturation deshields the sulfonyl oxygens in both five‐ and six‐membered rings.
EPR and ENDOR study of thermally produced triphenylmethyl radicals
Authors: Lewis I. C. , Singer L. S.
Published: May 2005

The ENDOR spectrum of the triphenylmethyl radical formed by heat treatment of triphenylmethane has been measured in solution at 131°C. The derived hyperfine coupling constants of 2.770, 2.556 and 1.138 G were used to simulate the extremely well resolved EPR spectrum. These coupling constants are in good agreement with spin densities determined for the planar radical by the McLachlan method.
AAEE case report #4: Guillain‐Barré syndrome
Authors: Albers James W.
Published: May 2005

A case report is presented of a 33‐year‐old woman who awoke with distal paresthesias, mild incoordination, and progressive weakness. Examination 3 days later demonstrated weakness of the extremities, which was greater in distal muscles than in proximal ones, mild facial weakness, distal vibratory loss, and areflexia. Electrodiagnostic studies provided evidence of an acquired demyelinating polyradiculoneuropathy of recent onset. Motor conduction studies revealed abnormal temporal dispersion and partial conduction block. Preserved sural responses with abnormal median sensory conduction studies supported the diagnosis of Guillain‐Barré syndrome, as did subsequent cerebrospinal fluid examinations documenting increasing total protein, identification of preceding cytomegalovirus injection with increasing serum convalescent titer, and progressive clinical improvement after a brief plateau. The role of electrodiagnosis in establishing the diagnosis and prognosis in Guillain‐Barré syndrome is reviewed.
The relationship of cold and warmth cutaneous sensation to age and gender
Authors: Doeland Herman J. , Nauta Jos. J. P. , van Zandbergen Johannes B. , van der Eerden Harriët A. M. , van Diemen Nico G. J. , Bertelsmann Frits W. , Heimans Jan J.
Published: May 2005

To evaluate cold and warmth cutaneous sensation separately, thermal discrimination thresholds (TDTs) for the foot were estimated for cold and warm stimuli in 71 normal subjects aged between 21 and 92 years. A “thermoaesthesiometer” operating on the Peltier principle was used. A rise of TDTs with age was found. Furthermore, female subjects appeared to have lower thresholds than males. Independent of age or gender, TDTs for cold stimuli were on average lower than for warm stimuli. In accordance with other studies, a large intraindividual variability was found, which emphasizes the necessity for repeated measurements.
Lipid peroxide and antioxidant enzymes in muscle and nonmuscle of dystrophic mouse
Authors: Asayama Kohtaro , Hayashibe Hidemasa , Dobashi Kazushige , Kato Kiyohiko
Published: May 2005

To determine whether abnormality in redox metabolism occurs specifically in certain individual dystrophic muscles, thiobarbituric acid reactivity, free radical scavengers, and oxidative marker enzymes were measured in the liver, kidney, erythrocytes, heart, and four different individual skeletal muscles from‐C57BL/6J dy/dy mice. Superoxide dismutases were assayed by specific radioimmunoassays, which enabled the study of a small individual murine muscle. Glutathione peroxidase and catalase were increased markedly in each individual dystrophic skeletal muscle studied and less markedly in the heart. Manganosuperoxide dismutase and thiobarbituric acid reactivity were decreased to a similar extent in each dystrophic skeletal muscle. Cuprozinc superoxide dismutase was decreased in the soleus muscle. Only a minimal biochemical change occurred in nonmuscles. Fumarase activity correlated closely with the level of manganosuperoxide dismutase. These results suggest that muscle protein breakdown occurs independently of lipid peroxidation despite the presence of tissue‐specific abnormality of redox metabolism in dystrophic muscle.
The effect of the internal reference on ASIS correlations: 2—The intrinsic ASIS of TMS protons in aromatic hydrocarbon solvents
Authors: Bertrán J. Fernández , Rodríguez Mario
Published: May 2005

A method is developed to calculate the intrinsic ASIS of TMS protons used as internal reference, based on linear correlation of the ASIS of a group of sensor protons in two fixed aromatic solvents. Several solute systems (p‐X‐benzaldehydes, camphor, α‐Br‐camphor, 5‐X‐furfurals, p‐X‐acetophenones and methyl ketones) are used to calculate a series of intrinsic ASIS values of TMS in 12 aromatic hydrocarbon solvents. The Δα TMS values are used, in turn, to calculate the intrinsic ASIS of CHO protons in dimethylformamide and diphenylformamide, and of the CH3 protons in diethyl ether and diisopropyl ether.
18O‐isotope effect in 13C nuclear magnetic resonance spectroscopy: 5—Substituent group electronic effects in substituted acetophenones
Authors: Risley John M. , DeFrees Shawn A. , Van Etten Robert L.
Published: May 2005

A series of para‐ and meta‐substituted acetophenones were prepared which were highly labeled with 18O at the carbonyl function. The natural abundance 13C NMR spectra of the compounds were recorded and the 18O‐isotope‐induced shifts of the carbonyl carbon were measured in order to determine possible substituent group electronic effects on the 18O‐isotope shift. The isotope shifts were found to be correlated with a number of properties which demonstrate the molecular basis of the isotope shift. Good correlations were obtained for the isotope shift as a function of σp+, the carbonyl stretching frequency, the carbonyl group bond order, the n→π**transition of the carbonyl group and the chemical shift of the ipso carbon. In contrast, no correlation was observed between the magnitude of the 18O‐induced isotope shift and the 13C chemical shift of the carbonyl carbon. These properties are discussed in connection with the theoretical basis of the isotope shift.
Accurate referencing of 13C NMR spectra from glycosaminoglycan and other polysaccharides in aqueous medium
Authors: Huckerby T. N.
Published: May 2005

The use of the water‐soluble reference materials sodium 2,2‐dimethylsilapentane sulphonate (DSS) and sodium 2,2,3,3,‐tetradeuterio‐3‐trimethysilyl propionate (TSP‐d4) as internal standards for the calibration of carbon spectra determined in D2O is proposed. Problems arising from the use of secondary or external references are eliminated; very high field spectra (13C at 100 MHz) may be calibrated to 0.01 ppm.
29Si NMR spectra of trimethylsilylated cyclic acyloins and ketones. 29Si chemical shifts as a measure of ring size
Authors: Schraml J. , Šraga J. , Hrnčiar P.
Published: May 2005

29Si chemical shifts are reported for nine 1,2‐bis(trimethylsiloxy)cycloalkenes and four 1‐trimethylsiloxycycloalkenes, (Me3SiO)xCnH2n–2–x (x=1, 2). For cycloalkene derivatives with n⩽8 the silicon shift exhibits a strong dependence on the ring size, although the silicon is exocyclic and is separated by two bonds from the olefinic carbon atom. The dependence can be exploited for ring size determination of cyclic ketones after trimethylsilylation.
Differentiation of diastereomeric bornane derivatives by 13C NMR spectroscopy
Authors: Duddeck Helmut , Blagoev Blagoy , Berova Nikolina D. , Vassilev Vassil
Published: May 2005

Three diastereomeric bornane derivatives have been assigned configurational structures by 13C NMR measurements in the presence of Yb(dpm)3.
Influence of the Z/E configuration on the 13C15N coupling conditions 1J(13C15N) in aromatic azo and diazo compounds
Authors: Simova S. , Fanghänel E. , Radeglia R.
Published: May 2005

The 13C NMR spectra of singly 15N‐labelled Z/E isomers of azo and diazo compounds were recorded. The 1J(13C15N) coupling constants are strongly dependent on the geometrical configuration of the azo group, the relative position of the lone pair of electrons at the non‐coupling azo nitrogen atom having a decisive influence.
Aza‐polycyclic aromatic hydrocarbons: 1—Elucidation of the regiochemistry of 1,2,3,4‐tetrahydroazabenz‐[a]anthracene‐7,12‐diones by long‐range carbon–proton coupling constants
Authors: Haber Arthur , Hilton Bruce D.
Published: May 2005

The 13C NMR spectra of 5,8‐quinolinedione, 6‐chloro‐5,8‐quinolinedione and 7‐chloro‐5,8‐quinolinedione have been examined in detail. Utilization of long‐range proton‐carbon coupling constants have allowed the unambiguous identification of the regioisomeric 8‐aza‐1,2,3,4‐tetrahydrobenz[a]anthracene‐7,12‐dione and 11‐aza‐1,2,3,4‐tetrahydrobenz[a]anthracene‐7,12‐dione.
13C chemical shifts of Δ1‐pyrrolines
Authors: Gawley Robert E. , Termine Enrico J. , Goicoechea‐Pappas Marta
Published: May 2005

13C chemical shifts are reported for the ring carbons of several substituted Δ1‐pyrrolines. Average values for methine and methylene ring carbons facilitate structure elucidation of substituted δ1‐pyrrolines by 13C NMR spectroscopy.
13C NMR spectra of benzothiazepinone, benzothiazinone and benzosulphonamide N‐substituted derivatives
Authors: Stassinopoulou C. I. , Catsoulacos P. , Camoutsis Ch.
Published: May 2005

A comparative study of the 13C NMR spectra of benzothiazinone and benzothiazepinone dioxide derivatives and of some structurally related benzosulphonamides is presented. The size of the heterocyclic ring is reflected in the 13C chemical shifts and in the one‐bond carbon‐proton aromatic coupling constants. An upfield γ‐effect of sulphur on the 13C chemical shifts in N‐substituted carboxyethylbenzene‐4,5‐dimethoxysulphonamides is reported.
A model for the complex of the (R)‐MTPA ester oftrans‐4‐tert‐butylcyclohexanol with Eu(fod)39based on lanthanide induced shifts
Authors: Vanhoeck L. , Merckx E. M. , Bossaerts J. , Lepoivre J. A. , Alderweireldt F. C.
Published: May 2005

It is shown that the complexation of Eu(fod)3with the MTPA ester oftrans‐4‐tert‐butylcyclohexanol is very similar to that of ketones with Eu(fod)3. It is found to be more likely that the MTPA moiety can exist as two rotamers, suggesting that earlier models for correlating LIS and absolute configuration are inadequate.
13C NMR spectra of some monosubstituted quinolizinium bromides
Authors: Van Veldhuizen A. , Van Dijk M. , Sanders G. M.
Published: May 2005

Chemical shifts are reported for quinolizinium bromide and 12 monosubstituted derivatives, carrying a bromohydroxy, diethylamino or piperidino group as the substituent. In addition, 1J(CH) values and long‐range coupling constants are given.
Electron spin resonance spectra and hyperfine coupling constants of the α‐tocopheroxyl and 2,2,5,7,8‐pentamethyl‐chroman‐6‐oxyl radicals derived from vitamin E and its model and deuterated model compounds
Authors: Matsuo Mitsuyoshi , Matsumoto Shigenobu , Ozawa Toshihiko
Published: May 2005

Highly resolved electron spin resonance spectra of the α‐tocopheroxyl or 2,2,5,7,8‐pentamethylchroman‐6‐oxyl radicals were obtained from the oxidation of α‐tocopherol (vitamin E) or its model compound, 2,2,5,7,8‐pentamethylchroman‐6‐ol, with 2,2‐diphenyl‐1‐picrylhydrazyl or superoxide ion. Complete assignments of the hyperfine coupling constants of these radicals were made on the basis of the spectra of the deuterated isotopomers of the 2,2,5,7,8‐pentamethylchroman‐6‐oxyl radical. The large coupling constant due to the methyl group at C‐5 in the α‐tocopheroxyl radical may have implications for the high reactivity toward radicals of C‐5 in α‐tocopherol.
Fluoroimines from the reaction of fluoro amino acids or fluoroketo acids with the aldehyde or amine form of vitamin B6: 2—Stereochemical aspects of their formation from β‐fluoroaspartates or β‐fluorooxaloacetate, using 19F NMR
Authors: Salon M. C. , Hamman S. , Beguin C. G.
Published: May 2005

The fluorine NMR spectra of systems initially containing 0.05–0.1 M of pyridoxal 5′‐phosphate and erythro‐β‐fluoroaspartate (or threo‐β‐fluoroaspartate) in D2O solution were examined over the pD range 1–12. The formation of the aldimine Schiff base gave only one stereoisomer, whcih was trapped with sodium borohydride. Reactions of pyriodoxamine 5′‐phosphate and fluorooxaloacetate were examined under the same conditions. A mixture of two products was given, identified as two ketimine Schiff bases (E and Z isomers) with well characterized fluorine chemical shifts and 2J(DF) values. This mixture, trapped with sodium borohydride, gives the two reduced erythro and threo aldimines. The configurations and conformations of all reaction products were determined using the 3J(HF) values and their correlation with the fluorine chemical shift. The role of the 3‐phenolate oxygen of the pyridine ring, of the conjugate acid of the iminium nitrogen and of the carboxylate oxygen in ionic or hydrogen bond interactions in the determination of the stereochemistry is discussed.
13C NMR studies of conformational isomerism in thioureas: Signal assignments via chemical shift and population trends
Authors: Sullivan Richard H. , Nix Pamela , Jun. Eddie L. Summers , Parker Stanley L.
Published: May 2005

The 22.63 MHz 13C NMR spectra of a series of alkylated thioureas are reported. Characteristic Z and E spectral regions were found for the 13C  S resonances. The two regions were generally found to be non‐overlapping for the series, with the region of the Z, Z resonances occurring more downfield than those of either the Z, E or E, Z conformers in the cases of 1,3‐disubstitution. The Z, Z configuration became favored and the relative chemical shift difference (Rδ) increased linearly with increasing substituent size. At 217 K, hindered internal rotation caused a multiplicity of resonances which were normally single peaks in the broad band 1H decoupled 62.86 MHz 13C spectrum of CH3NHCSNH(CH2)2NHCSNHCH3 (2MTE) at room temperature. The trends in chemical shifts and populations were employed to assign tentatively the resonances of five of the six possible configurational isomers contributing to the 2MTE spectra at 217 K. The isomer populations are given. The 13C NMR spectra reported here led to signal assignments of Z and E isomers which supported prior 1H NMR results and contradicted more recent results of another 13C NMR study of N‐methylthiourea. The major peak of the exchange doublet occurs at relatively high field strengths in both methanol‐d5.
1H NMR study of 2,8‐dithia‐1,5‐dielementbicyclo[3.3.0]octanes
Authors: Zschunke A. , Mügge C. , Meyer H. , Tzschach A. , Jurkschat K.
Published: May 2005

The analysis of the 1H NMR spectra of 2,8‐dithia‐1,5‐diphosphabicyclo[3.3.0]octane, 2,8‐dithia‐1‐phospha‐5‐azabicyclo[3.3.0]octane and 2,8‐dithia‐1‐arsa‐5‐phosphabicyclo[3.3.0]octane is supported by means of 2D‐ J‐resolved NMR measurements. The spectra suggest a preferred conformer with strong puckering of the fused five membered rings.
A carbon‐13 NMR study of the ion pair structure of the dibenzo[b,f]pentalene dianion
Authors: Eliasson Bertil , Edlund Ulf
Published: May 2005

The 1H and 13C NMR chemical shifts of dibenzo[b, f]pentalene and its 5,10‐dimethyl derivative are presented and compared with those of the corresponding dilithium dianions. As probed by the relative 13C NMR chemical shifts, the charge distribution within the dianion system is clearly dependent on the actual ion pair state. This condition is demonstrated by varying the solvent and temperature. The polarization of charge towards the pentalene carbons, i.e. the preferred cation positions, is observed on going to tight ion pair conditions. Further support for this model is gained from 7Li NMR. The limitations of the use of 1H and 13C NMR chemical shifts to measure charge distributions within anion systems are discussed.
Solution conformation and dynamics of L‐6‐methylperhydroimidazo[1,5‐c]thiazole‐5,7‐dione (γ‐thiaprolinehydantoin). A 1H and 13C NMR study
Authors: Borremans Frans A. M. , Buděšínský Milos , Callens Roland E. A. , Anteunis Marc J. O.
Published: May 2005

The solution conformation of L‐6‐methylperhydroimidazo[1,5‐c]thiazole‐5,7‐dione (γ‐thiaprolinehydantoin) has been determined from an extensive 1H and 13C NMR study, allowing the extraction of vicinal inter‐proton and carbon‐hydrogen coupling constants. The major conformation of the thiazolidine ring is an envelope with C‐δ as the flap exo (δ−). In solution the preferred solid state (twist) conformer with C‐α exo and C‐β endo (αβT) is only a minor contributor. 13C spin–lattice relaxation data reveal the flexibility of the thiazolidine ring.