Computational Studies on Reactions of Some Organic Azides with C H Bonds.

The computational methods, B3LYP and MP2 with the basis set 6-311+ +G(d,p) have been used to decipher the energetics and mechanisms of different nitrene reactions, namely organic azide decomposition, singlet and triplet nitrene addition to different kinds of C H bonds, azide insertion into C H bonds and substitution reaction of azides to alkanes. The addition of singlet nitrene to the C H bond is exothermic, with one-step addition accompanied by a considerable barrier, where the sequence of facility H>Ac>Me indicates the electrophilic nature of the nitrene reactant. In the case of triplet nitrene, the initial step involves smaller barriers and is endothermic due to the formation of radicals as intermediate products, and the final step involves the coupling of radicals and is hence exothermic. The direct azide addition has higher barrier then the stepwise addition reaction. The Hammond postulate can be used to differentiate the transition state geometries for different reaction steps as “early” or “late". [ABSTRACT FROM AUTHOR]