Effect of ortho substituents on carbonyl carbon ~13CNMR chemical shifts in substituted phenyl benzoates

摘要

andphenyl moiety, 4 ortho-substituted methyl and 5 ethyl benzoates as well as 9 R-substituted alkyl benzoates have beenrecorded. The influence of the ortho substituents on the carbonyl carbon~13CNMR chemical shift,hp,was found to bedescribed by a linear multiple regression equation containing the inductive, o_1,resonance,0-R,and steric,g,or vsubstituent constants. For all the ortho-substituted esters containing substituents in the acyl part as well as the phenylpart, the substituent-induced reverse inductive effect (ρ_10), and negativesteric effect (ε-ortho < 0) with the g were observed. In the case of ortho substituents in the phenyl part, the resonanceeffect was negligible. Due to inductive effect, the ortho electron-withdrawing substituents showed an upfield shift orshielding of the carbonyl carbon, while the electron-donating substituents had an opposite effect. Because of thesterical consequences, ortho substituents revealed a deshielding effect on the ~13CNMR chemical shift of the carbonylcarbon. For all the meta- and para-substituted esters, the reverse substituent-induced inductive and resonance effects(A < 0, pR < 0) were found to be significant. In alkyl benzoates, the alkyl substituents showed the reverse inductive andsteric effects. The log k values for the alkaline hydrolysis in water, aqueous 0.5 M Bu4NBr and 2.25 M Bu4NBr, and the IRfrequencies, vco, for the ortho-, meta-, and para-substituted phenyl benzoates and alkyl benzoates were correlatednicely with the corresponding