The ESR spectra of p-RCH2-substituted phenoxy radicals (1) can be interpreted in terms of a radical mechanism involving CH and (for 1g) CP hyperconjugation. Evidence for a hindered rotation around the CP bond is furnished by the temperature dependence of the ESR spectrum of 1g at −85 to +100°. The phenoxyls are dehydrogenated to p-quinone methides (2). Temperature dependent NMR spectra are only
p -RCH 2取代的
苯氧基自由基(1)的ESR光谱可以用涉及CH和(对于1g)CP超共轭的自由基机理来解释。围绕CP键旋转受阻的证据是在-85至+ 100°时1g的ESR光谱对温度的依赖性。苯氧基被脱氢为对醌甲基化物(2)。与温度相关的NMR光谱仅在直接或通过
乙烯基键结合的对-双醌甲基化物2k和21中观察到。计算出绕环CC双键旋转的活化自由焓分别为2k和21时为26和20 kcal / mol 。由于旋转的结构先决条件,因此认为涉及双自由基过渡态。