. Can. J. Chem. 53,373 (1975). 13C and lH spectra have been determined for 18 4-substituted phenylacetylenes and carbon charge densities have been estimated by CND0/2 molecular orbital calculations. Correlations of these parameters with a, and aRO indicate that the important mechanisms of transmission of substituent effects are field, resonance, and w polarization effects, as previously noted for 4-substituted styrenes. Evidence is presented that demonstrates that both IH and 13C chemical shifts for these compounds reflect ground state charge densities. CND012 calculations on a variety of aromatic derivatives suggest that the a, dependence of I9F chemical shifts in these derivatives may primarily be due to rr polarization. Chem. 53,373 (1975). On a dttermin6 les spectres r.m.n. du lH et du I3C de 18 ph6nyIacCtylbnes substitu6s e n position 4 et on a estim6 les densites de charge au carbone par des calculs d'orbitales mol6culaires CND012. Les corrdlations de ces parametres avec a, et a," montrent que les mdcanismes important de transmission des effets des substituants sont des effets de champ de r6sonance et d e polarisation rr tel que not6 antkrieurement pour des styrbnes substituks en position 4. Les donndes sont prdsentkes pour d6montrer que les dkplacements chimiques du proton et du carbone 13 pour ces composts rkfletent les densit6s de charges it 1'6tat fondamental. Les calculs CND012 sur un grand nombre de derives aromatiques suggkrent que la d6pendance des d6placements chimiques du I9F sur a, dans ces d6rivds peut ktre due principalement a une polarisation rr.[Traduit par le journal] IntroductionWe recently utilized n.m.r. spectral parameters (measured under inert conditions) and all-valence electron molecular orbital calculations to determine mechanisms of transmission of substituent effects in a series of 4-substituted styrenes and a-alkylstyrenes (1, 2). It was concluded that field effects, resonance effects, and n inductive (polarization) effects are all important in determining electronic distributions in these molecules.Classical electric field calculations (3), CND0/2 molecular orbital calculations (4), and correlations of l H and 13C chemical shifts with field (F) and resonance (R) divided substituent parameters (DSP) (5) were used to determine mechanisms of transmission of substituent effects in styrenes. If chemical shift -DSP correlations are valid (see refs. 6 and 7 for objections to the approach), then the weighting factors for closely related systems should vary in a manner which is consistent with the proposed

Comparisons of 'H chemical shifts and charge densities (determined by C N D 0 / 2 MO calculations) for 4-substituted derivatives of styrene, toluene, benzylchloride, and N,N,N-trimethylphenylammonium ion indicate that the chemical shifts primarily reflect intramolecular electronic effects. These effects are reflected by correlations of 'H chemical shifts with the F and R reactivity parameters of Swain and Lupton. It is concluded that it is valid to correlate substituent-induced chemical shifts for aromatic derivatives with divided reactivity parameters provided that ( I ) chemical shifts are measured at infinite dilution in a non-polar medium and'(2) at least ten derivatives of each family are investigated.Calculations for 4-substituted toluenes indicate that there will be a small conformational dependence for substituent-induced benzylic proton chemical shifts.La comparaison des deplacements chimiques ' H et des densites de charge (dktermintes par la mkthode CNDO/2 MO) pour des derives substitues en position 4 du styrene, du toluene, du chlorure de benzyle et de I'ion N,N,N-trimkthylphinyl ammonium indiquent que les deplacements chimiques refletent principalement les effets Clectroniques intramolCculaires. Ces effets apparaissent sous forme de correlation entre les deplacements chimiques 'H avec les parametres de rkactivite F e t R de Swain et Lupton. On en conclut qu'il est valide de faire une correlation entre le substituant et les diplacements chimiques induits dans les derives aromatiques possedant des parametres de reactivite divises pourvu (I) q u e les deplacements chimiques soient mesurks dilution infinie dans un solvant non-polaire et (2) qu'au moins dix derives de la famille soient etudits.Les calculs pour les toluenes substituCs en position 4 indiquent qu'il y a une petite dependance conformationnelle pour les dkplacements chi~niques des protons benzyliques qui ont ett induits p a r les substituants.[ (1) derivatives) should reflect resonance effects since R = 0 for the N(CH,),+ group (3). They also [I]

The n.m.r. spectra of eight 1,2-dihaloalkanes have been determined in solvents of differing polarity. The relative rotamer stabilities for each compound have been deduced from the variation of the difference and sum of vicinal coupling constants with solvent. Variations in geminal and long range coupling constants with solvent are also attributed to conformational changes.Les spectres de r.m.n. de huit dihalogeno-1,2 alkanes ont ete determines dans des solvants de polarite differente. Les stabilites relatives des rotameres de chaque compose ont 6te determintes en fonction des variations de la difference et de la somme des constantes de couplage vicinale selon le solvant. Les variations, selon lc solvant, des constantes de couplage geminale et a longue distance sont Cgalement attribuables aux modifications conformationnelles.

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