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Obtaining thermochemical data by the extended kinetic method
Author(s) -
Bouchoux Guy,
Sablier Michel,
BerruyerPenaud Florence
Publication year - 2004
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.680
Subject(s) - chemistry , protonation , logarithm , thermodynamics , kinetic energy , proton , entropy (arrow of time) , computational chemistry , reaction rate constant , denticity , base (topology) , kinetics , organic chemistry , physics , quantum mechanics , mathematics , ion , mathematical analysis , crystal structure
A microcanonical analysis of the extended kinetic method is performed using statistical rate calculations based on orbiting transition state theory. The model systems simulate polydentate bases M which exhibit losses of entropy upon protonation of up to 35 kJ mol −1 K −1 . It is shown that the correlations using the natural logarithm of the ratio of rate constants vs the proton affinity of the reference bases, at several effective temperatures, lead to correct proton affinity and protonation entropy of the base M of interest. A systematic underestimate of the latter quantity (by 5–15%), mainly due to the use of a linear rather than a polynomial curve fitting procedure, is noted, however. When considering experimental data, more severe underestimates are observed for the protonation entropies of polydentate bases (by 50–90%). The origins of these considerable discrepancies are beyond the limits of the present modeling and remain to be determined. Copyright © 2004 John Wiley & Sons, Ltd.