X-Ray crystallographic and infrared spectroscopic evidence for the electronic structure of the 1,5-diamino-1H-1,2,4-triazolo[1,5-c]quinazolinium cation

Abstract

The crystal structure of the title cation (1) shows it to possess a system of strongly localised alternant double bonds which can be interpreted in terms of a dominant pseudo-quaternary canonical form. Its i.r. spectrum contains a doublet near 1 700 cm^–1 which is interpreted, on the results of deuteriation, as ν(CN⁺) coupled with δ(NH₂) and with other ring modes. The electron distribution revealed by both techniques helps to explain the high and localised reactivity of the cation.