Abstract: | Absolute rate constants and their temperature dependencies were determined for the addition of hydroxymethyl radicals (CH2OH) to 20 mono- or 1,1-disubstituted alkenes (CH2 = CXY) in methanol by time-resolved electron spin resonance spectroscopy. With the alkene substituents the rate constants at 298 K (k298) vary from 180 M?1s?1 (ethyl vinylether) to 2.1 middot; 106 M?1s?1 (acrolein). The frequency factors obey log A/M?1s?1 = 8.1 ± 0.1, whereas the activation energies (Ea) 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 k298/M?1s?1 = 5.57 + 1.53 · EA/eV (R2 = 0.820) and Ea = 15.86 ? 7.38 · EA/eV (R2 = 0.773), hydroxymethyl is a nucleophilic radical, and its addition rates are strongly influenced by polar effects. No apparent correlation was found between Ea or log k298 with the overall reaction enthalpy. © 1995 John Wiley & Sons, Inc. |