Theoretical Studies on the Protonation Equilibria of Benzoyl Derivatives

Bulletin of the Korean chemical society

Chang Kon Kim¹  Yong Bin Kim¹  Bon-Su Lee¹  Wang Ki Kim¹ 

关键词: Protonation equilibria;    Benzoyl derivatives;    Ortho-methyl substituent;    B3LYP/6-31+G*;    NRT analysis.;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

The effects of ortho- (R = H and CH₃) and Y-substituents (Y = OCH₃, CH₃H and CN), which are directly attached to the carbonyl carbon, on the protonation equilibria of the para-X-substituted benzoyl derivatives, 4-X-2, 6-di-R-C₆H₂-C(=O)-Y, are investigated theoretically using the B3LYP method with 6-31+G^* basis set. Structurally, both of the (B) and (BH⁺ ) forms in the species with R = H are nearly coplanar regardless of the Y-substituents implying that the steric repulsion between Y-substituent and R = H is relatively small. In the species with R = CH₃ , the tortional angle (�?) between the carbonyl moiety and aryl ring varies from zero to near right angle depending on the degree of steric repulsion between Y and R = CH₃ and the resonance demand. However the reaction energies, ツG�?, for the protonation processes are more favorable for R = CH₃ than for R = H due to stronger electron donating effect of R = CH₃ , although the species with R = CH₃ are unfavorable sterically. On the other hand, the Hammett type plots are progressively better correlated with �?⁺ than with �? values on going from Y = OCH₃ to Y = CN for both species with R = H and CH₃ indicating that the degree of resonance delocalization between carbonyl moiety and X-substituent is increased for a more electron accepting Y-substituent. Nevertheless the effects of R = CH₃ on the magnitude of Hammett type reaction constants ( �? or �?⁺ ) are not much different from those of R = H.

【 授权许可】

Unknown