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Substituent Effects on Phosphate‐Catalyzed Proton Exchange in Amides
Author(s) -
Wang WeiHsien,
Cheng ChingChih,
Lee MingChao,
Huang ChiungYi
Publication year - 1991
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.199100059
Subject(s) - chemistry , substituent , catalysis , phosphate , proton , medicinal chemistry , kinetics , concerted reaction , organic chemistry , computational chemistry , stereochemistry , physics , quantum mechanics
The kinetics of phosphate‐catalyzed proton exchange have been measured with NMR lineshape analysis for a series of amides, ureas, and carbamates. A hypothetical energy profile for transition structures of concerted phosphate catalysis ‡ c and of stepwise phosphate catalysis ‡ 1 , ‡ 2 is used for discussion of the substituent effects. The concerted mechanism of phosphate catalysis operates only for amides RCONHCH 3 for which the electron‐donating ability of the substituent R is comparable with, or better than, that of the methyl group. We conclude that concerted phosphate catalysis is inoperative in proteins or polypeptides.