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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 21, Number 9
BKCSDE 21(9)
September 20, 2000 

Transmission of Substituent Effects through Five-Membered Heteroaromatic Rings,II. Deprotonation Equilibria of Phenol Analogues
Chang Kook Sohn, Sun Hee Lim, Soon Ki Rhee, Chang Kon Kim, Chan Kyung Kim, lkchboon Lee*
Transmission of substituent effects through 5-membered heteroaromaticrings isinvestigated theoretically at the RHF/6-31+G* and B3LYP/6-31+G* levelsusing the deprotonation equilibria of phenol analogues with heteroatoms Y = NH, O, PHand S. The increase in the resonance delocalization of the πlone-pair on the phe-nolic oxygen atom, nπ(O), accompanied with the deprotonation depends on the heteroatom Y,in the order NH < O < PH < S. This represents the πelectron accepting ability, or conversely reverse order of the πelectron donating ability of the πlone-pair on Y, nπ(Y). The transmission efficiency of substituenteffects is, however,in the reverse order NH > O > S, which represents the order of delocalizability of nπ(Y). A better correlation is obtained with σp - than with σp for the Hammett type plots with the positive slope, ρ- > 0, of the magnitude in the same order as that for the delocalizability of nπ(Y). Thedeprotonation energy, ΔG = [G(PA) + G(H+)] -G(P), decreases with the increasein the extence delocalization in the order NH > O > PH > S.
891 - 895
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