I t is surprising to see both tert-butyl salts showing greater reactivity than the unsubstituted salt. However, this may be rationalized on the basis that the transition state for either 3a and 3b in the rate-determining step leading to the oxides shows less crowding, due to the presence of the tert-butyl group, than does the initial salt; ie, the ground-state energy of 3a or 3b is higher than for 15.
[Tasz, Maciej K.; Gamliel, Asher; Rodriguez, Oscar P.; Lane, Thomas M.; Cremer, Sheldon E.; Bennett, Dennis W. Journal of Organic Chemistry, 1995 , vol. 60, # 20 p. 6281 - 6288]
