摘要:

AbstractThe equilibrium rotamer populations and NN rotational barriers ofN‐nitrosopyrrolidine (1),N‐nitrosothiazolidine (2),N‐nitrosooxazolidine (3) and their 2‐methyl derivatives, 4, 5 and 6, were determined by13C NMR spectroscopy. While equal rotamer populations occur in 1 and 2, theErotamers predominate in the other four compounds, with the highest percentage (92%) ofErotamer occurring inN‐nitroso‐2‐methyloxazolidine (6). The average barrier to NN bond rotation varies over a range of 4.1 kcal mol−1in these compounds, decreasing in the orderN‐nitrosopyrrolidine>N‐nitrosothiazolidine>N‐nitrosooxazolidine. The compounds which contain an exocyclic 2‐methyl group have average rotational barriers which are 0.1–0.9 kcal mol−1higher than those of the corresponding unmethylated derivatives. The results are interpreted in terms of the relative effects of steric hindrance by the 2‐methyl substituents and electron induction by the heterocyclic sulfur and oxygen atoms on both the rotamer population

ISSN:0030-4921    

DOI:10.1002/omr.1270210202

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractThe1H NMR spectra of several six‐coordinate cobalt(III) porphyrins of general formula L2Co(DPDME)CI, where DPDME=deuteroporphyrin dimethyl ester and L is an optically active ligand, have been measured at 250 or 400 MHz. In a few cases, two signals of equal intensity are observed for the L ligand protons. This magnetic non‐equivalence, which never exceeds 0.04 ppm, is thought to arise from the planar chirality of the porphyrin ring, which makes a proton in the ligand L above the porphyrin ring and the corresponding proton below this ring diastereoto

ISSN:0030-4921    

DOI:10.1002/omr.1270210203

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

Abstract13C NMR spectra of thiols, sulfinic acids, sulfinyl chlorides, sulfonic acids and sulfonic anhydrides have been obtained. The data are discussed in terms of the additivity of the deshielding effects exerted by the sulfur functionality at the α‐ or β‐position, and the shielding effects produced by the sulfur function at the γ‐

ISSN:0030-4921    

DOI:10.1002/omr.1270210204

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of 62 oxanes (tetrahydropyrans) with and without methyl substituents at various ring positions, some of them bearing in addition (or instead) ethyl, vinyl, ethynyl, carbomethoxy and methylol substituents at C‐2, have been recorded, and the 294 resulting chemical shifts have been correlated by multiple linear regression analysis. Axial and equatorial α‐, β‐, γ‐, δ‐,gem‐ andvic‐parameters for shifts caused by methyl groups at all ring positions, and similar parameters for Et,—CHCH2,—CCH, CO2Me and CH2OH groups at C‐2, are reported. Standard deviations of the parameters are, in most cases, within 0.3 ppm and the agreement of calculated and experimental shifts is excellent. This is probably the largest parameter set of this type extant.13C NMR spectra of a number of additional substituted tetrahydropyrans, and of 3,6‐dihydro‐2H‐pyrans and 3,4‐dihydro‐2

ISSN:0030-4921    

DOI:10.1002/omr.1270210205

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

Abstractα‐Pinene and β‐pinene13C enriched at the C‐10 position were prepared by an unambiguous synthesis.13C NMR spectral analysis provided evidence for a revised assignment for α‐pinene at the C‐9 and C‐1

ISSN:0030-4921    

DOI:10.1002/omr.1270210206

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractThe polypeptide carbobenzoxy‐glycyl‐L‐prolyl‐L‐leucyl‐L‐alanyl‐L‐proline (0.2Min DMSO‐d6) was investigated using13C,1H and15N NMR in natural abundance at 4.7 tesla. The existence ofcis–trans‐Gly‐Pro and ‐Ala‐Pro bonds permits up to four isomers, and all four were observed (in a 60:30:7:3 ratio).13C shifts of the proline β‐CH2resonances are consistent only with the 60% form beingtrans–trans. The 30% form is eithertrans–cisorcis–trans(order as above) and was tentatively assigned ascis‐transon the basis of relaxation behavior. Refocused INEPT studies aided the13C assignments. The15N data were obtained using both NOE and INEPT excitation, with signals evident for the three major isomers. The spectra were analysed by starting from the13C data, which were assigned based on known regularities in peptide spectra. A13C1H heteronuclear two‐dimensional chemical shift correlation experiment allowed direct assignment of proton shifts for major and minor isomers. The NH proton shifts were assigned by running a homonuclear two‐dimensional chemical shift correlation experiment and noting the correlation with the previously assigned α‐CH protons. The15N resonances were then assigned from a15N1H heteronuclear two‐dimensional chemical shift correlation experiment, relating the15N signals directly to the NH proton resonances. Isomer interconversion between the two major isomers was demonstrated by performing a magnetization transfer homonuclear 2D experiment. Off‐diagonal intensity was noted relating the major and minor isomer alanine NH proton, as we

ISSN:0030-4921    

DOI:10.1002/omr.1270210207

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractThe assignments of the13C NMR shift values of the dihydrobenzofuranoid lignans cedrusin and dihydrodehydrodiconiferyl alcohol, their respective 4‐O‐β‐D‐glucosides and their acetates have been made. The furanoid stereochemistry in 8,3′‐lignans could be deduced from comparative

ISSN:0030-4921    

DOI:10.1002/omr.1270210208

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractThree diastereomeric bornane derivatives have been assigned configurational structures by13C NMR measurements in the presence of Yb(dpm)3.

ISSN:0030-4921    

DOI:10.1002/omr.1270210209

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractINDO parameterized calculations, employing phosphorus s, p and d valence orbitals, are reported for values of1J(PC) and1J(PF) relating to phosphorus in formal tri‐ and pentavalent states. The1J(PC), interactions are mainly controlled by the contact term. Thus, trivalent phosphorus compounds have negative values for1J(PC), whereas those for pentavalent phosphorus are positive due to the s lone‐pair effect. The inclusion of phosphorus 3d orbitals is shown to be important for an understanding of the processes contributing to1J(PF) interactions.1J(PF) values are shown to be negative for both tri‐ and pentavalent phosphorus compounds. The contact and orbital interactions are significant for the trivalent phosphorus molecules, whereas in the pentavalent phosphorus case1J(PF) is dominated by the orbital

ISSN:0030-4921    

DOI:10.1002/omr.1270210210

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractThe13C 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 andnJ(13C15N) values were used for the assignment of the signals of the aromatic carbon

ISSN:0030-4921    

DOI:10.1002/omr.1270210211

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY