A new estimate of π < inf> 2 (N < inf> 2 ) for prediction of activation parameters for homolysis of azo compounds

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The activation parameters for homolysis of trans-azo compounds (azoalkanes, hyponitrites, and tetrazenes) can be related to thermodynamic quantities by the equation E′ (kcal/mol) = 29.65 + ΔHf°(X·) - 0.5ΔHf°(X2N2), where E′ is the intercept at log A/s = 15.1 in linear plots of Ea vs. log A within a related series of azo compounds. Except for azoalkanes with groups more branched than tert-butyl, the equation correctly predicts E′ to within 1.1 kcal/mol in about half of 21 examples. Values of E′ = 37.5 and 38.9 kcal/mol are calculated for homolysis of trans-(HON=)2 and N2F2, for which no kinetic data are available. © 1985 American Chemical Society.

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Journal of Physical Chemistry