Hydrogen-deuterium isotope electronic states

If there is only one step, the reaction has to be second order first order in the peracid and first order in the alkene. The reaction rate has very little dependence upon the solvent, supporting a concerted mechanism with little charge developing at the transition state. The small charge development is also supported by the fact that the rates correlate with a Hammett parameter a ), but the p value is only -1.1 for p-XArCH=CH2. There are only small primary kinetic isotope effects. Values of Ath/Ato around 1.1 to 1.2 are found for the peracid [ROiHfD)]. This means that the hydrogen atom transfer shown in the electron pushing of Scheme 10.5 has to be either minimal at the transition state or almost complete (see Section 8.1.2). Secondary deuterium isotope effects on the alkene carbons are inverse, as may be expected for an sp- to sp transformation. 

The slower rate (by a factor of 1.8) of decomposition of deuterogermane shows then that deuterium desorbs more slowly (by the same factor) than hydrogen from a germanium surface. This factor is consistent with normal zero-point energy differences for hydrogen isotop>es. The existence of a kinetic isotope effect for desorption is what is expected from a normal activated thermal-bond breaking and does not support the idea that the activation energy corresponds to some barrier which electrons have to surmount, possibly caused by a barrier layer due to adsorption surface states (5). 

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