Theoretical investigations on stability of pyridylpentazoles, pyridazylpentazoles, triazinylpentazoles, tetrazinylpentazoles, and pentazinylpentazole searching for a replacement of phenylpentazole as N5 (-) source.

Stabilities of pyridylpentazoles, pyridazylpentazoles, triazinylpentazoles, tetrazinylpentazoles, and pentazinylpentazole were studied using density functional theory to assess their potentials as the source of pentazole anion (N5 (-)) for replacement of phenylpentazole (PhN 5 ). Replacing the aryl group of PhN 5 by six-member heterocycle weakens pentazole ring. Compared to PhN 5 , title molecules have longer N-N bonds and lower activation energy (E a,1) needed for the N5 ring breaking. E a,1 decreases with the increasing number of nitrogen atoms of heterocycle. The ortho nitrogen of heterocycle most obviously lowers the stability of pentazole. The central C-N bond dissociation energies (BDEs) of title molecules are lower than that of PhN 5 . For the molecule with 0~1 ortho-nitrogen, H rearrangement happens during the central C-N bond breaking. The energy (E a,2) required for H rearrangement is considerably smaller than the corresponding BDE. ΔE a,2 (E a,2(PhN5) - E a,2 = 7.5~35.7 kJ mol(-1)) is larger than ΔE a,1 (E a,2(PhN5) - E a,2 = 4.6~15.5 kJ mol(-1)), while ΔE a,2/E a,2(PhN5) (2~9.5 %) is smaller than ΔE a,1/E a,1(PhN5) ( 4.4~15.0 %). The larger ΔE a,1/E a,1(PhN5) suggests that title molecules can not be the better N5 (-) than PhN 5 .