摘要:

AbstractThe non‐bonded interactions which occur between solute and solvent molecules are discussed and the various models which describe the interactions are presented. The models are employed, within a quantum chemical framework, to estimate the extent of medium effects on chemical shifts and spin‐spin couplings. Comparison between the calculated and available experimental data is provided for some first row nuc

ISSN:0030-4921    

DOI:10.1002/mrc.1270150202

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractWhile there is a useable paramagnetic relaxation reagent (PARR) for use in nonpolar or low polarity solvents, there has not been a practical PARR for use in highly polar solvents. A reagent, Gd(NO3)3‐inositol, is described which appears to satisfy this need. The performance of the reagent is given in terms of its effect on theT1, NOE and line width values ofN,N‐dimethylformamide. In addition, the application of this reagent to adenosine is also repor

ISSN:0030-4921    

DOI:10.1002/mrc.1270150203

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

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

ISSN:0030-4921    

DOI:10.1002/mrc.1270150204

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe configuration and stable conformation of two dibenzylidene‐L‐iditol isomers formed upon benzalation ofL‐iditol, as well as that of a third isomer obtained by partial hydrolysis of the tribenzylidene derivative—the main product of the benzalation reaction—were determined by1H and13C NMR spe

ISSN:0030-4921    

DOI:10.1002/mrc.1270150205

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe compoundstrans‐NPCl2−n(NMe2)n(NSOPh)2(n=0‐2iNPCl2−nNMe2)n(NSOPh)2(n=0‐2) and N2P2Cl4−nl4−n(NMe2)nNSOP2P2Cl4−n(NMe2)nNSOPh(n=0‐4), were prepared from their chloro‐precursors. The substitution follows a completely non‐geminal pathway, and all possible isomers are formed. The observed relative abundance of these isomers shows that the phenyl group exhibits a strong directing effect on the incoming amine. The1H,31P and13C NMR spectra of the most abundant isomers are reported.2J(CP) couplings within the PNMe2grouping are affected by the number of substituents at the phosphorus atom. Almost linear relationships exist between the degree of substitution and the chemical shift of C‐1 and C‐4 of the phenyl groups. The effect of substitution on the13C chemical shifts of these groups is ascr

ISSN:0030-4921    

DOI:10.1002/mrc.1270150206

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe barriers to internal rotation about the CN bond in several thiopiperidides have been determined by the NMR technique. It was found that the barrier height (ΔG T c‡) increases in the series cinnamoylthiopiperidide

ISSN:0030-4921    

DOI:10.1002/mrc.1270150207

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

Abstracto‐Carbonyl benzeneselenenyl compounds with COCH3, CHO and COOCH3as carbonyl functions and SeCl, SeBr, SeSCN, SeSeCN, SeCN and SeCH3as selenium‐containing groups, have been studied by1H,13C and77Se NMR spectroscopy. The IR CO stretching frequencies of these compounds are also reported. If the SeCH3derivatives are excluded, the compounds mainly adopt a planar ‘cis’ conformation, due to an interaction between the CO group and the selenium atom. The range of over 800 ppm for the observed77Se chemical shifts makes77Se NMR spectroscopy a powerful tool for physical organ

ISSN:0030-4921    

DOI:10.1002/mrc.1270150208

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractCarbon‐13 NMR spectra of mono‐ and dichloro‐hexanes and mono‐ and dichloro‐heptanes are reported. Substituent effects for α, β and γ positions are presented. Differences between the13C chemical shifts of diastereoisomers are observed in the cases of 2,4‐ and 2,5‐dicholohexanes and 2,4‐, 2,5‐ and

ISSN:0030-4921    

DOI:10.1002/mrc.1270150209

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractHuman serum albumin has been specifically acetylated using aspirin in which the methyl carbon of the acetyl group was enriched to 90%13C. A single resonance at 23.13 ppm downfield from tetramethylsilane was observed in13C differences spectra obtained at both 25.2 and 45.3 MHz. Chemical shift studies of several model compounds suggest that this is the resonance position to be expected for an acetamide group exposed to solvent. The line width observed for the enriched methyl resonance is consistent with free rotation of the methyl group.

ISSN:0030-4921    

DOI:10.1002/mrc.1270150210

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe15N NMR spectra of various oligopeptide derivatives of the ZXYYOMe structure, where X and Y are variable amino acids and Z is the benzyloxycarbonyl group, were measured in several protic and aprotic solvents. The shift difference of the15N of the YY and XY bond (neighbouring residue effect) is discussed with respect to the nature of X and Y with respect to the solvent. Oligopeptides of the ZXYYOH and n̊H3XYYOMe structures were compared with the Z‐pëptide esters to investigate the spectroscopic influence of the protecting groups. The methyl ester hydrochlorides of the 25 most common amino acids were measured in water and DMSO to elucidate the solvent dependence of the substituent effects. Moreover, the methyl ester hydrochlorides were compared with Z‐amino acids andN‐acetyl‐amino acid methyl esters in DMSO to establish whether the substituent effects depend on the nature of the amino acid derivatives. In this connection the assignments of the serine, threonine and glycine signals are discussed with respect to silk proteins. Furthermore, the assignments of the signals of copolypeptides by comparison with oligo‐ and homo‐polypeptides are discussed. Finally, it was demonstrated that intramolecular H bonds cause downfied shifts

ISSN:0030-4921    

DOI:10.1002/mrc.1270150211

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY