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Absolute rate constants for the addition of hydroxymethyl radicals to alkenes in methanol solution
Author(s) -
Wu J. Q.,
Fischer H.
Publication year - 1995
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550270207
Subject(s) - chemistry , reaction rate constant , radical , hydroxymethyl , enthalpy , methanol , alkene , medicinal chemistry , photochemistry , analytical chemistry (journal) , kinetics , organic chemistry , catalysis , thermodynamics , physics , quantum mechanics
Absolute rate constants and their temperature dependencies were determined for the addition of hydroxymethyl radicals (CH 2 OH) to 20 mono‐ or 1,1‐disubstituted alkenes (CH 2 = CXY) in methanol by time‐resolved electron spin resonance spectroscopy. With the alkene substituents the rate constants at 298 K ( k 298 ) vary from 180 M −1 s −1 (ethyl vinylether) to 2.1 middot; 10 6 M −1 s −1 (acrolein). The frequency factors obey log A /M −1 s −1 = 8.1 ± 0.1, whereas the activation energies ( E a ) range from 11.6 kJ/mol (methacrylonitrile) to 35.7 kJ/mol (ethyl vinylether). As shown by good correlations with the alkene electron affinities (EA), log k 298 /M −1 s −1 = 5.57 + 1.53 · EA/eV (R 2 = 0.820) and E a = 15.86 − 7.38 · EA/eV (R 2 = 0.773), hydroxymethyl is a nucleophilic radical, and its addition rates are strongly influenced by polar effects. No apparent correlation was found between E a or log k 298 with the overall reaction enthalpy. © 1995 John Wiley & Sons, Inc.