Transmission of substituent effects through five-membered heteroaromatic rings, II. Deprotonation equilibria of phenol analogues

Title
Transmission of substituent effects through five-membered heteroaromatic rings, II. Deprotonation equilibria of phenol analogues
Authors
Kim, C.K.
Keywords
heteroaromatic rings
Issue Date
2000-09
Publisher
BULLETIN OF THE KOREAN CHEMICAL SOCIETY
Abstract
Transmission of substituent effects through 5-membered heteroaromatic rings is investigated theoretically at the RHF/6-31+G* and B3LYP/6-31+G* levels using the deprotonation equilibria of phenol analogues with heteroatoms Y = NH, O, PH and S. The increase in the resonance delocalization of the pi lone-pair on the phenolic oxygen atom, n(pi)(O), accompanied with the deprotonation depends on the heteroatom Y, in the order NH < O < PH < S. This represents the pi electron accepting ability, or conversely reverse order of the pi electron donating ability of the pi lone-pair on Y, n(pi)(Y). The transmission efficiency of substituent effects is, however, in the reverse order NH > O > S, which represents the order of delocalizability of n(pi)(Y). A better correlation is obtained with sigma(p)(-) than with sigma(p) for the Hammett type plots with the positive slope, rho(-)>0, of the magnitude in the same order as that for the delocalizability of n(pi)(Y). The deprotonation energy, Delta G = [G(PA) + G(H+)] - G(P), decreases with the increase in the extent of resonance delocalization in the order NH > O > PH > S.
URI
http://dspace.inha.ac.kr/handle/10505/20168
ISSN
0253-2964
Appears in Collections:
College of Natural Science(자연과학대학) > Chemistry (화학) > Journal Papers, Reports(화학 논문, 보고서)
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