N‐Oxides of Polyazoles and Polyazines

Abstract

The N‐oxide bond, which will be written as N→O, is formally coordinate covalent, with both electrons being provided by a covalently bonded nitrogen. A more realistic description is that the nitrogen lone pair is polarized toward the oxygen by the electric field of the latter. Our present focus is upon the N‐oxides of polyazoles and polyazines, particularly those having three or more linked (catenated) nitrogens. The N→O linkage is inductively electron withdrawing. In resonance delocalization, it is intrinsically a donor of electronic charge although this can be partially countered by electron‐donating substituents. A significant feature of the N→O linkage is that it can somewhat mitigate the destabilization associated with nitrogen catenation. This is discussed in terms of the molecular electrostatic potentials. N‐oxides of polyazoles and polyazines can be prepared by oxidizing the heterocyclic precursors; the sites can to some extent be predicted in terms of local ionization energies (or local polarizabilities), but other factors can also be involved. The current interest in N‐oxides as high explosives is briefly discussed.

Theoretical Studies on Energetic Nitrogen‐Rich Heterocyclic Substituted Derivatives of Pyrazino [2, 3‐e] [1, 2, 3, 4] Tetrazine‐1, 3‐di‐N‐oxide

“…One of the destabilizing factors in polyazoles and polyazines is to transfer the lone pair electrons on adjacent nitrogen atoms. The effective way of shifting these lone pair electrons to other non‐nitrogen atoms is the introduction of N‐oxides . The idea that the N‐oxide can enhance the stability of the polyazines was verified theoretically by Wilson and his research group .…”