Ionic and Radical Intermediates

The application of quasi-steady-state and quasi-equilibrium hypotheses will be illustrated with the example reaction 

The vectors for chemical symbols are fixed to = [A B D]anda = [A ]. The generation rates of the main components are given by 

The expression for ca is inserted into the expression for Ri (or R2), and the final rate equation is obtained  

We thus obtain a rate equation in which the intermediate does not appear anymore and the generation rates of the components are calculated from n = ViR, where v, denotes the stoichiometric coefficients of the main components (va = vb = — 1 and vd = 1). 

From the general solution obtained with the quasi-steady-state hypothesis, the solutions corresponding to the quasi-equilibrium hypothesis can be obtained as special cases. If step I is much more rapid than step II, fc i fc+2CB in Equation 2.27, the reaction rate becomes 

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In the dibenzoylperoxide decompositions the effects are caused in pairs which are themselves part of a minor reaction pathway. The same may be true for other reactions, especially of the rearrangement type where ionic and radical intermediates may be present simultaneously. CIDNP effects are evidence for radical intermediates, though others may be present as well, and for quantitative studies CIDNP has to be combined with other techniques to elucidate the relative importance of various possible pathways. 

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