摘要:

AbstractThe COLOC‐S pulse sequence (a modification of COLOC) provides rapid and selective long‐range correlation 2D NMR spectra. It combines the advantages of the COLOC and Freeman sequences. This modification is analysed in terms of the Product Operator Formalism, and its application is illustrated by spectral peak assignments of two insecticides, ryanodine and 1R,cis‐pheno

ISSN:0749-1581    

DOI:10.1002/mrc.1260251002

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractA NOESY‐type experiment with multiple mixing periods and acquisitions within a single pulse sequence was used to obtain a complete NOE correlation map of a small organic molecule. Incorporating multiple mixing periods and acquisitions into a single sequence can eliminate the need for repeating NOESY experiments with different mixing periods to observe dipolar exchange of considerably different rates or to determine exchange rates. The sequence has been applied to the molecular structure elucidation ofcis‐8a‐vinyloctahydro‐3H‐2‐benzopyran‐3,7‐dione, a small organic molecule where the use of a single mixing period does not reveal all protons undergoing d

ISSN:0749-1581    

DOI:10.1002/mrc.1260251003

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractComparison of the1H and13C chemical shift data of bryonolic acid (D : C‐friedoolean‐8‐en‐3β‐ol‐29‐oic acid) and its derivatives (13 species) revealed that the conformational features of these compounds in CDCl3solution depend on whether the functional groups at C‐29 are trigonal, such as COOCH3, or tetrahedral, such as CH2OH. In order to study the conformational features of these two groups of compounds, vicinal coupling constants between the protons on the E rings of the methyl ester of D : C‐friedoolean‐8‐en‐29‐oic acid, D : C‐friedoolean‐8‐en‐29‐oic and its acetate were measured. Comparison of the results with the steric geometries to be expected from the molecular mechanics calculation for the E‐ring moieties of these derivatives in the S form (D‐E rings: boat‐boat form) and the F form (D‐E rings: chair‐chair form) led to the conclusion that the compounds having a trigonal functional group at C‐29 mainly adopt the S form, and those having a tetrahedral functional group at C‐29 are present as mixtures o

ISSN:0749-1581    

DOI:10.1002/mrc.1260251004

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe preferred conformations and, for the 3‐methyl‐substituted analogues also the configurations of the C‐3 atom, for 3‐unsubstituted and 3‐methyl‐substituted di‐exo‐ and di‐endo‐annellated oxazepinone derivatives fused with a norbornane or norbornene skeleton were determined by1H and13C NMR spectroscopy, including the use o

ISSN:0749-1581    

DOI:10.1002/mrc.1260251005

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe previously reported finite perturbation MNDO/GIAO method was ued to calculate nuclear magnetic shielding constants. A set of atomic MNDO parameters for nitrogen and oxygen was chosen by comparing calculated and experimental chemical shifts for compounds containing N and O atoms. The agreement of the trends within these compounds was satisfactory.

ISSN:0749-1581    

DOI:10.1002/mrc.1260251006

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe neutral and the protonated, positively charged, forms of 7‐methylguanosine have been characterized by15N NMR in dimethyl sulphoxide. It is shown that in this solvent protonated 7‐methylguanosine gives specific interactions with cytidine at the same sites as those involved in the guanosine‐cytidine Watson‐Crick base‐pairs present in nucl

ISSN:0749-1581    

DOI:10.1002/mrc.1260251007

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

Abstract1H NMR spectra oft‐3‐ethyl‐r‐2,c‐6‐diphenylpiperidine,t‐3‐ethyl‐r‐2,c‐6‐diphenyl‐4‐piperidone and several related compounds have been obtained in deuteriochloroform and deuteriotrifluoroacetic acid solutions, and compared with the spectra of their hydrochlorides in deuteriochloroform‐hexadeuteriodimethyl sulphoxide solutions. The effects of the structural changes 4‐CH2→ have been observed on the chemical shifts of ring and substituent protons, and on the non‐equivalence of the diaster

ISSN:0749-1581    

DOI:10.1002/mrc.1260251008

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractA new method is presented for the assignment of the NMR resonances of the diastereotopic protons in tetrahydrofur‐furyl and pyrrolidinylmethyl groups, based on the conformational transmission effect This effect describes the conformational changes produced by an increase of coordination from four to five of a phosphorus, silicon or germanium atom attached to the tetrahydrofurfuryl or pyrrolidinylmethyl moieties. The1H NMR conformational analysis of these cyclic four‐ and five‐coordinated compounds yields two possible results, based on two assignments of the diastereotopic proton resonances. Comparison with the conformations of the analogous four‐ and five‐coordinated systems with acyclic 2‐methoxyethyl and dimethylaminoethyl groups (which lack diastereotopic protons) directly shows which assignment is correct, since a similar conformational transmission occurs in both the cyclic and the acycli

ISSN:0749-1581    

DOI:10.1002/mrc.1260251009

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractMultinuclear NMR data (1H,13C,119Sn) have been obtained for almost all possible isomers of the composition Me3Sn(C3Hm)SnMe3(m= 2, 4, 6) and Me3Sn(C4Hn)SnMe3(n= 0, 2, 4, 6, 8). The coupling constantsxJ(Sn, Sn) (x= 4, 5) are not linearly related to the corresponding coupling constantsxJ(H, H), but are particularly large when tin‐carbon bonds can interact hyperconjugatively with carbon‐carbon double or triple bo

ISSN:0749-1581    

DOI:10.1002/mrc.1260251010

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractA refined version of the IPPP‐INDO method was used to analyse the difference betweencisandtrans13C‐31P couplings in phosphorus‐substituted alkenes. A large through‐space transmission of the Fermi contact term is predicted for thecis13C‐31P coupling. With the new version of the IPPP method it was assessed how different orbitals, describing chemically intuitive bonds, lone pairs and antibonding orbitals, contribute to the Fermi contact term. The importance of the P lone pair and C‐H bonds was clearly determined. The antibonding orbitals, which are very important but rarely mentioned, are als

ISSN:0749-1581    

DOI:10.1002/mrc.1260251011

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY