ELECTRONIC-STRUCTURES OF 1,2,3,5-THIATRIAZEPINE-1,1-DIOXIDE AND 1,2,3,5-BENZOTHIATRIAZEPINE-1,1-DIOXIDE

1, 2, 3, 5-thiatriazepine-1,1-dioxide 1 is formally a homoaromatic ana logue of 1, 2, 4-triazine which is known to be aromatic. However, elec tronic structure calculations, carried out at the HF/6-31G* and MP2/6 -31G* levels, indicate that 1 is neither planar nor aromatic. The lac k of aromaticity in 1 is reflected in bond lengths and covalent bond o rders that exhibit large degrees of alternation, Similar conclusions a re reached for the 1, 2, 3, 5-benzothiatriazepine-1,1-dioxide molecule 2, in which only the benzene ring is found to be aromatic.