Theoretical studies on the protonation equilibria of benzoyl derivatives

Title
Theoretical studies on the protonation equilibria of benzoyl derivatives
Authors
Lee, B.S.
Keywords
protonation equilibria, benzoyl derivatives
Issue Date
2001-04
Publisher
BULLETIN OF THE KOREAN CHEMICAL SOCIETY
Abstract
The effects of ortho- (R = H and CH3) and Y-substituents (Y = OCH3, CH3 H 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 (theta) 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, DeltaG degrees, 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 sigma (+) than with sigma 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 (p or rho (+)) are not. much different from those of R = H.
URI
http://dspace.inha.ac.kr/handle/10505/20189
ISSN
0253-2964
Appears in Collections:
College of Natural Science(자연과학대학) > Chemistry (화학) > Journal Papers, Reports(화학 논문, 보고서)
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