Rate constants for the addition of the 2-cyano-2-propyl radical to alkenes in solution

Absolute rate constants for the addition of the 2-cyano-2-propyl radical to 26 alkenes CH₂=CXY at 315 K were determined in solution by time-resolved electron-spin-resonance spectroscopy. They vary with the alkene substituents from 30 M^?1 s^?1 to 7′010 M^?1 s^?1. For styrene the temperature dependence is given by log k/M^?1 s^?1 = 7.7 ? 26.1/Θ where Θ = 2.303 RT in kJ/mol. An analysis of the substituent effects in terms of polar and enthalpic factors reveals a dominant influence of the overall reaction enthalpy. © 1993 John Wiley & Sons, Inc.