Ab initio studies of a 1,2,3,5-tetrazocine

COMP 207

Sarah A Kebbell, sarah.kebbell2@mail.dcu.ie and Dermot F Brougham. School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Dublin, Ireland
Tetrazocines are eight-membered rings possessing four nitrogen atoms. Tetrazocines do not occur in nature, so the synthesis of these compounds is a novel idea in itself. James et al[1] have successfully synthesised a 1,2,3,5 tetrazocine molecule from the photo-rearrangement of a substituted hexahydropyrrolo-[2,3-d]triazole to a 1,3a,6,6a-tetrahydroimidazo [4,5-c]pyrazole. Ab initio molecular orbital calculations have been performed on 1,2,3,5 tetrazocines at the HF/3-21G and the B3LYP/6-31G* levels, in order to obtain more information on the physical properties of these systems. Our results indicate that for the 1,2,3,5 tetrazocine the planar (aromatic) structure is the most stable, though this is not observed in nature, presumably due to steric repulsion between the large aromatic substituents often used to stabilise the molecules. Excluding this structure we found that at the B3LYP-6-31G* level, there is a significant 42.64kcal/mol, thermodynamic stabilisation of 1,2,3,5 tetrazocine over the 1,3a,6,6a-tetrahydroimidazo [4,5-c]pyrazole.

1. Byrne, C.; Draper, S.M.; James, J.P.; Long, C. J Chem. Research. 1995, 2501