The pKa of Pentazole (HN5).

Pentazole having the molecular formula HN5 is an archetypical five-membered homocyclic inorganic aromatic molecule consisting of five nitrogen atoms. A hydrogen atom is bonded to one of the nitrogens. Even though the molecule does not contain a carbon it appears last in the series of the heterocyclic azole family; the family containing one to five nitrogen atoms. This series of heterocyclic azoles is pyrrole, imidazole, pyrazole, triazole, tetrazole, and the last one is the pentazole. Barring pentazole, the rest of the members of the azole family are heterocyclic organic molecules. The p K a of N(1)H-acidity values of all the azole members are known, except for that of pentazole. In the present work we endeavoured to determine the p K a of pentazole by a graphical method and by performing theoretical DFT calculations. Addition of every pyridine type nitrogen (= N–) to the azole ring increases the N(1)–H acidity. This idea led to determining the p K a of pentazole by graphical extrapolation. In addition to this, theoretical calculations were performed to calculate the p K a of pentazole. The p K a of pentazole estimated by different methods is reported in this article. [ABSTRACT FROM AUTHOR]