A QUANTITATIVE INVESTIGATION OF OZONOLYSIS REACTION .8. ON DIRECTION OF CLEAVAGE OF PRIMARY OZONIDES OF SELECTED UNSYMMETRICAL OLEFINS

The cleavage of the primary ozonides of a series of unsymmetrical olefins, R1C6H4CH=CHR2, has been studied. The proportions of the two ways of cleavage to yield (a) R1C6H4CHO + R2C+HOO¯ and (b) R1C6H4C+-HOO- + R2CHO have been found to be related to Hammett's ó and ρ constants by the equation [formula-omitted], providing the compounds involved have a common R2, substituent (x = proportion of cleavage following route a; [formula-omitted] = Gibbs activation energy difference between assumed transition states of the primary ozonide, when R1 = H). An interpretation of the Hammett relationship and of the behavior of the R2 groups in terms of transition states concludes that the zwitterion, which is formed preferentially, is the one whose en ironment is better able to stabilize the positive charge by increasing the electron density in the vicinity of the potential zwitterionic carbocation (in the transition state) via inductive and mesomeric effects. The relative efficiencies of the R2 groups in stabilizing zwitterions can be placed in the order COCH3 > CH3 > COOH > Ph > H > CH2OH > COOCH3. The behavior of the groups COCH3 and COOH, which tend to stabilize the zwitterions R2C+HOO- despite the fact that they are electron-withdrawing groups, is explained by resonance stabilization. © 1969, American Chemical Society. All rights reserved.