Ab initio SCF molecular orbital calculations have been performed to ascertain the conformational preferences of protonated, neutral, and deprotonated amidine [HC(NH)NH2], using the 3‐21G split valence basis set. The states of eight stable species, eight transition states, and four higher‐order saddle points have been determined by complete geometry optimization utilizing analytic energy gradient techniques. Protonation at the amidine NH is preferred over the –NH2 site by 37.1 kcal/mol. Neutral amidine has rotational barriers of 9.6 and 11.7 kcal/mol for the HNCN cis and trans isomers, respectively, while all the stable HC(NH2)2+ and HC(NH)2− species possess torsional barriers larger than 23 kcal/mol. There is, however, essentially free C—N single‐bond rotation in HC(NH)NH3+, the calculated barriers being 0.7 and 1.8 kcal/mol for the cis and trans HNCN isomers, respectively.
ASJC Scopus subject areas
- Computational Mathematics