摘要:

AbstractThe substituent influence on the1H and13C NMR chemical shifts in 2‐substituted benzimidazoles and their anions and cations has been investigated. The transmission of the electronic effects of substituents from C‐2 to C‐5 (6) is approximately 20% less effective than that in the opposite direction. The solvent influence on the chemical shifts of protons and transmission effects in the charged forms of 2‐substituted benzimidazoles has been

ISSN:0030-4921    

DOI:10.1002/mrc.1270150302

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractA13C NMR study of a series of 3‐aryl‐2‐thioxo‐4‐imidazolidinones, which are capable of existing as enantiomeric or diastereomeric rotational isomers about the aryl CN bond, shows that rates of internal rotation are slow at the probe temperature. The effects of hetero‐ and aryl‐ring substituents on hetero‐ring carbon atoms have

ISSN:0030-4921    

DOI:10.1002/mrc.1270150303

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractLow temperature13C NMR spectra of 80:20 mixtures ofcisandtrans‐4CH3CH3C6H10CH2X, where C6H10‐is 1, 4‐disubtituted cyclohexyl and X=Br, CN, OH, OCH3, Si(CH3)3, Sn(CH3)3, Pb(CH3)3and HgOCOCH3have been recorded. The signals of thetrans(e, e) components were assigned from the ambient temperature spectra of C6H11CH2X and the established substituent effects of an equatorial methyl group in cyclohexane. Conformational equilibria of thecis(e, a⇄a, e) components were then computed from the intensities of the (remaining) signals (∼180 K) of the two conformational isomers. From these equilibriaAvalues of CH2X were calculated, assuming additivity of conformational energies of CH3and CH2X (the counter‐poise approach). In general, these values are very similar to the value of the CH3, although some trends do emerge. This study provides α, β, γ, and δ effects for a wide range of axial and

ISSN:0030-4921    

DOI:10.1002/mrc.1270150304

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe NMR spectrum of phenazine, the tricyclic diazine, oriented in a nematic phase is investigated. The ratios of the interproton distances are determined. They do not deviate significantly from the corresponding values in quinoxaline oriented in a thermotropic solvent.

ISSN:0030-4921    

DOI:10.1002/mrc.1270150305

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractHigh precision14N nuclear screening data are presented for some alkyl‐ and aryl‐N‐sulphinylamines. For the alkyl compounds the β effect is seen to produce a decrease in screening and the opposite influence from the γ effect is also observed. An exception to the general tendency for the β effect is noted for (CH3)3CNSO. CNDO/S parameterized nitrogen screening calculations show that for this molecule the distortedcisform, with all of the methyl carbons rotated out of the CNSO plane, is the most probable structure. A similar effect is observed upon substituting the bulkytert‐butyl group in the 2 position of the aryl compounds studied. Nitrogen screening calculations again indicate the presence of the distor

ISSN:0030-4921    

DOI:10.1002/mrc.1270150306

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe13C chemical shifts of 2‐substituted and 2,6‐disubstituted anthraquinones have been determined and assigned. The C‐1, 2, 3, 4, 13 and C‐14 chemical shifts of 2‐substituted anthraquinones are correlated with the chemical shifts of monosubstituted benzenes. A three‐parameter correlation with Swain and Lupton's ℱ and ℛ parameters and Schaefer'sQparameter provides relationships for the prediction of all chemical shifts of 2‐substituted anthraquinones from the substituent parameters.Qvalues for the SCH3, OCOCH3, C2H5and C(CH3)3groups are proposed. The two types of correlations are compared for predictin

ISSN:0030-4921    

DOI:10.1002/mrc.1270150307

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe19F substituent chemical shifts (SCS) of a series ofpara‐phenylacetyl fluorides (XPhCH2COF) are reported and compared with the related benzoyl fluoride series (XPhCOF). A dual substituent parameter analysis of the results for the new series shows that both inductive and resonance effects are reduced by one third when compared with the benzoyl fluorides.13C shifts for the side chain carbonyl were also measured and found to follow a reversed trend in substituent effects, consistent with a pi polarization mechanism. SCS values for the fluorine and its adjacent carbon are not directly related.Ab initio(STO‐3G) calculations of the carbon and fluorine electron density for this series have been compared with the appropriate SCS values. From the electron densities and the observation that the fluorine SCS values follow a normal direction, whilst those for electron densities and the observation that the fluorine SCS values follow a normal direction, whilst those for the adjacent carbon are reversed, it is concluded that fluorine SCS values (and Δqπ values) result from polarization of the CF pi bond and do not merely monitor changes in electron density of th

ISSN:0030-4921    

DOI:10.1002/mrc.1270150308

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe1H NMR spectra of naphthalene as an eight spin system, and two of its derivatives, 2,4‐dichloro‐ and 2,4‐dinitro‐1‐naphthol, have been completely analysed. The Indor technique has been very useful in the determination of the signs and magnitudes of very small coupling constants. An improved version of the Laocoon 3 program has greatly facilitated the spectral analysis through, first, the knowledge of the dependence of each transition upon the spectral parameters; second, some modifications in the iterative loop which avoid failure of convergence, and, third, the use of a slightly modified diagonalization subroutine which saves 20% CPU computer time. Our data suggest a rather small substituent effect on intra‐ring couplings of the unsubstituted ring. The inter‐ring coupling constants display a negative or positive sign according to an even or odd number of intervening bound, except the all‐trans6Jwhich is positive. No substituent effect on the inter‐ring couplings has been observed, except a small effect fo

ISSN:0030-4921    

DOI:10.1002/mrc.1270150309

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractIsomeric mixtures of compounds MenM(CHCHMe)4−n(M=Si, Pb; n=0−3) have been prepared and studied, as well as pure Me3M(CMeCH2) and mixtures containing propenyl isopropenyl residues bonded to silicon and lead.1H,13C,29Si and207Pb NMR data are presented; as previously observed for the corresponding tin compounds, the29Si and207Pb shifts for the Me3MC3H5isomers can be used to calculate the shifts expected for the other isomers; while for lead the agreement is good, calculated and observed values for silicon diverge with decreasingndue, at least in part, to steric

ISSN:0030-4921    

DOI:10.1002/mrc.1270150310

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractAn equation has been developed which relatesorthoor C‐β13C substituent chemical shifts (SCS) to theorthoproton–proton coupling constant in the unsubstituted member of a conjugated series. This method is an extension of previous equations which have been used to predictortho1H SCS values, and has its origin in a relationship between bond order and SCS values. The equation was derived fromortho13C data in 2‐naphthalenes and monosubstituted benzenes and its application to other unsaturated series is dis

ISSN:0030-4921    

DOI:10.1002/mrc.1270150311

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY