摘要:

Abstract13C screening constants and their anisotropies are calculated within the CNDO/S framework by using gauge dependent atomic orbitals in the molecular orbital description. The calculations include the excited singlet states which are mixed with the ground state by an external magnetic field. Reasonable agreement with available experimental data is obtained in most cases. Comparisons with someab initioresults are also made.

ISSN:0030-4921    

DOI:10.1002/mrc.1270090502

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractSome nitrogen screening constants and their anisotropies are calculated within the CNDO/S level of approximation. Satisfactory agreement is found with available experimental data in most cases. In general the reported results are in closer agreement with experiment than are those found fromab initiocalculations. The calculated data for the isoelectronic molecules N2O and CH2N2would be in better agreement with experiment if the assignments of the two nitrogen nuclei were reversed in both cases. A reasonable correlation is obtained with some observed nitrogen chemical shifts. Contributions arising from electronic transitions are reported for N2, HCN, CH3CN, CH3NC, NO2+and NO2

ISSN:0030-4921    

DOI:10.1002/mrc.1270090503

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractPour les R‐3 et R‐5 acétoxy‐1 cyano‐4 cyclohexène D2‐6,6trans, les fractions molaires des conformères diéquatoriaux ont été évaluées: 0,83 (méthyl‐3), 0,68 (méthyl‐5), 0,57 (t‐butyl‐3) et 0,55–0.69 (t‐butyl‐5). Pour les deux derniers composés, les valeurs des constantes de couplage sont compatibles avec l'hypothèse d'équilibres ee⇄aa. Pour les isomèrescis, les conformères à groupement alkyle équatorial sont prédominants (fraction molaire 0,76 pour méthyl‐3 et méthyl‐5) ou exclusifs (t‐butyl‐3‐butyl‐5). Par contre, l'acétoxy‐1t‐butyl‐3 méthoxycarbonyl‐45 cyclohexènecisprésente une hétérogénéité conformationnelle. L'enthalpie libre conformationnelle du gr

ISSN:0030-4921    

DOI:10.1002/mrc.1270090504

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractTous les paramètres RMN sont déterminés pour les dérivés suivants du diméthyl‐1,6 bicyclo[4.1.0]heptane: diméthoxycarbonyl‐3,4 (3 diastéréoisomères), méthoxycarbonyl‐3 (d4‐2,2,5,5)cisettrans, méthyl‐3 méthoxycarbonyl‐3cisettrans; les triméthyl‐1,5,5 bicyclo[4.1.0]heptanols‐3cisettransont été également étudiés. Les divers déplacements chimiques sont corrélés grǎce à un ensemble d'incréments déterminés empiriquement. Les équilibres conformationnels sont précisés à partir des constantes de couplage vicinales; les enthalpies libres conformationnelles du groupement COOCH3sont évalué

ISSN:0030-4921    

DOI:10.1002/mrc.1270090505

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractIn the reactions of Grignard reagents andn‐butyllithium the presence of transition metals and complexing solvents facilitates the formation of anion radicals. High radical concentrations, observable for some days at laboratory temperature, and very well resolved e.s.r. spectra of the following structural types have been obtained using a relatively simple procedure: aromatic hydrocarbons, heteroaromatics, aldehydes, ketones, α‐diketones, enolates of β‐diketones, quinones, sulphones, sulphoxides, nitro‐, nitroso‐ and azo‐benzenes, cyano compounds and phosphine oxides. It is suggested that the transition metals, according to the type of reactants and the experimental conditions, mediate the transfer of one electron to the substrate in many reactions and stabilize the intermediate products as anion radicals. The variation of solvents and organometallic compounds modifies the reduction power of such systems and leads to the radical products in a different reduction state. The procedure described is advantageously employable in the generation of anion radicals, and the effect of transition metals which has been found may widen the scope of this phenomenon to many different

ISSN:0030-4921    

DOI:10.1002/mrc.1270090506

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe conformations of the isopropyl groups and the barriers to conformational interconversion in methylN,N‐diisopropylcarbamate, its thiol and seleno analogues have been studied by1H d.n.m.r. In the diselenocarbamate, complete bandshape analysis of the Se‐methyl proton signals proves unequivocally that the conformational interconversion takes place by rotation of one isopropyl group at a time rather than by a concerted rotation of both groups. The populations and barriers observed for the new compounds fit well into the general scheme found previously for otherN,N‐diisopropylamides and ‐thi

ISSN:0030-4921    

DOI:10.1002/mrc.1270090507

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe13C chemical shifts of the diazanaphthalenes have been recorded as a function of the pH value, providing classical titration curves. From these curves the pK1and pK2values have been determined taking into account the activity coefficients. The changes in13C chemical shift under the influence of nitrogen protonation (Δδ) can be described by two protonation parameter set

ISSN:0030-4921    

DOI:10.1002/mrc.1270090508

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe13C n.m.r. spectra of 53 thianium,S‐methylthianium,S‐alkylthianium andS‐methyl‐1‐thiadecalinium salts, most of them substituted with methyl groups in the ring, have been recorded. The chemical shifts of the ring carbons in these thianium andS‐methylthianium salts and theS‐methyls in theS‐methylthianium salts have been analyzed in terms of additive parameters of the methyl substituents which are compared to those previously determined for the parent thianes. Comparison is also made with other

ISSN:0030-4921    

DOI:10.1002/mrc.1270090509

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe13C,29Si and119Sn chemical shifts of 2‐ and 2,5‐substituted organometallic (M=C, Si, Ge, Sn, Pb) derivatives of furan were measured. The most important factors, determining the specific features of the studied spectra, are d‐orbital availability and atomic radius of the central atom M, as well as the relatively higher (as compared with benzene) energies of the π‐electron energy levels of the fu

ISSN:0030-4921    

DOI:10.1002/mrc.1270090510

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

ISSN:0030-4921    

DOI:10.1002/mrc.1270090501

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY