ISSN:0030-4921    

DOI:10.1002/mrc.1270080716

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

ISSN:0030-4921    

DOI:10.1002/mrc.1270080718

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

ISSN:0030-4921    

DOI:10.1002/mrc.1270080719

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractThe temperature dependence of the geminal H,H coupling constant in solutions of α‐chloroacetophenone, α‐bromoacetophenone, 1‐bromo‐3‐chloro‐1‐phenylpropan‐2‐one and 1,3‐dibromo‐1‐phenylpropan‐2‐one has been determined at temperatures between 230 and 404 K. The values indicate that in the chloromethyl ketones the conformer with halogen and oxygen eclipsed is favored over that with hydrogen and oxygen eclipsed, while in the bromomethyl ketones the two conformers are of more nearly equal energy. The use of geminal coupling constants to indicate conformational preferences in substitu

ISSN:0030-4921    

DOI:10.1002/mrc.1270080702

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractLe phénomène d'inversion de l'azote a pu être mis en évidence par RMN du proton dans un certain nombre d'aziridines NH diversement C‐substituées. Lorsque l'encombrement des deux faces du petit cycle est trop différent, un seul invertomère existe. A partir des différents déplacements chimiques et des constantes de couplages HCNH, on peut constater que l'invertomère privilégié, ou unique, est toujours celui pour lequel le proton NH est du côté du cycle le moins encombré. Pour les aziridines symétriques, la barrière d'inversion a été mesurée: elle est abaissée lorsque l'encombrement stérique augmente. Dans les dérivés C‐phénylés un facteur supplémentaire de stabilisation des invertomères apparaît, sans doute dû à des conformations

ISSN:0030-4921    

DOI:10.1002/mrc.1270080703

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractD.n.m.r. studies have been performed involving the measurement of rates oftrans‐cisisomerization of aliphatic enamino ketones of the type RCOCHCHNHR1, by means of equilibration experiments and the method of finding the coalescence temperature. Simultaneous observation of the rates of dynamic NH proton exchange and isomerization processes by the latter method has facilitated the assignment of the rate‐determining reaction step in the title compounds studied in aprotic solvents. Thermodynamic parameters are discussed and the dipolar transition state to isomerization in a nonpolar solvent indicated. The dynamic behaviour of all protons undergoing exchange between the possible sites in the molecule are discussed in the light of our own experiments and othe

ISSN:0030-4921    

DOI:10.1002/mrc.1270080704

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

Abstract15N chemical shifts were measured in a series of anilinium fluorosulfonate salts and compared with chemical shift data from a comparable series of15N‐enriched aniline derivatives. A smaller overall range of nitrogen chemical shifts was observed for the protonated aniline series compared with that for the unprotonated anilines and is attributed to the elimination of nitrogen lone pair delocalization in the former series. Further‐more, it was found that the range of nitrogen chemical shifts in the protonated anilines is determined primarily by substituent electronic effects from theorthoring position with almost negligible contributions from theparaposit

ISSN:0030-4921    

DOI:10.1002/mrc.1270080705

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractLa résonance magnétique du77Se a été observée dans vingt‐six composés organiques dont certains contiennent un atome de séléniumendocyclique. Nous avons pu ainsi compléter l'échelle de déplacements chimiques établie par McFarlane. II apparaît difficile de définir une gamme de déplacement chimique du77Se caractéristique de son état de valence ou de sa positionendo‐ ouexocyclique. Certains résultats sont discutés qualitativement. Dans le cas du sélénolo [2,3‐b]thiophène, des arguments en faveur d'un couplage4J(Se, H) à travers l'atome

ISSN:0030-4921    

DOI:10.1002/mrc.1270080706

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

Abstract13C n.m.r. chemical shifts and carbon‐proton coupling constants of 2‐substituted pyrimidines are reported. The carbon chemical shifts are correlated with π‐electron densities. Substituents which cause deshielding at the directly bound carbon (e.g. NH2, OCH3and F) exert a more powerful effect in the benzene series than in the pyridine or pyrimidine series. The carbon‐proton coupling constants do not correlate with the electronegativity of the substituents. Carbon‐proton coupling constants and proton‐proton coupling constants over the same number of bonds do not obey the Karabatsos relationship. The changes in the carbon‐proton coupling constants in 2(1H)‐pyrimidinone and 2(1H)‐pyrimidinethione which accompany anion and cation form

ISSN:0030-4921    

DOI:10.1002/mrc.1270080707

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractThe conformations in solution of 6‐phenyltetrahydropterin, 6,7‐diphenyltetrahydropterin and 6‐7, dimethyltetrahydropterin have been determined from their proton magnetic resonance spectra. The 6‐phenyltetrahydropterin has the reduced pyrazine ring in a half chair conformation with the phenyl ring in the equatorial position. Both the 6,7‐diphenyl‐ and 6,7‐dimethyltetrahydropterins are of thecisconfiguration and have one substituent in an axial position. The enzymatic activity of these cofactors may be related to these

ISSN:0030-4921    

DOI:10.1002/mrc.1270080708

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY