A Theoretical Study of Thionitrosyl Azide (N 3 NS), Thiazyl Azide (N 3 SN) and Nitrosyl Azide (N 3 NO)

Stimulated by the recent detection of nitrosyl azide (N 3 NO), we investigated the stability of the sulfur analogues thionitriosyl azide (N 3 NS) and thiazyl azide (N 3 SN) by using ab initio MO calculations up to the QCISD(T)/6‐311+G(d)//QCISD/6‐311G(d) + ZPE level. Both azides have a similar energy content. While thionitrosyl azide is not stable with respect to N 2 elimination, thiazyl azide resists to this process by an energy barrier of about 110 kJ/mol. The NS and N 3 fragments resulting from homolytic cleavage lie about 100 kJ/mol above the azides. The five‐membered ring is thermodynamically much more stable than both azides but kinetically unstable with respect to cheletropic decomposition yielding N 2 S + N 2 . Overall, trans ‐thiazyl azide is the most likely candidate for experimental observation of, for example, the reaction of NS + salts with the azide anion. IR wavenumbers of the azides were also predicted.