ABSTRACT:The thermal decomposition of formyl, acetyl, and benzoyl azides to the corresponding isocyanate and nitrogen has been treated theoretically using ab initio molecular orbital calculations at the Møller-Plesset type 2 (MP2)(full)/6-31G* level. The reaction is stimulated by elongation of NON bond and is followed until the formation of the isocyanate and expulsion of nitrogen. The decomposition of formyl azide proved to be a concerted one-step reaction without the formation of a nitrene intermediate. In contrast, the conversion of both acetyl and benzoyl azides to the corresponding isocyanate and nitrogen is a two-step reaction, and a nitrene intermediate is formed. One transition state is located and identified during the course of the conversion of formyl azide, but two transition states are located and identified during the course of the conversion of acetyl and benzoyl azides. The thermodynamic functions, ⌬E r and ⌬H r , of the studied reactions are calculated. The results predict that the ease of conversion of the acyl azide to the isocyanate and nitrogen goes in the order: formyl azide Ͼ acetyl azide Ͼ benzoyl azide.