The structure and aromaticity of 1,4 and 1,5 dihydro diazocine, dioxocine, hydro oxazocine: ab initio CCSD(T) singlet potential energy surface study

Abstract The search for a minima on the ab initio CCSD(T) singlet potential energy surface of 1,4- and the hitherto unknown 1,5-dihydro diazocine, oxazocine, and dioxocine was performed. The calculations predict planar 1 H ,4 H -1,4-diazocine and 4 H -1,4-oxazocine, and nonplanar 1,4-dioxocine as the lowest energy isomers that were in agreement with experimental observations. Energy lowest structures of 5 H -1,5-oxazocine, 1 H ,5 H -1,5-diazocine, and 1,5-dioxocine were planar. The calculations confirm the aromaticity of 1 H ,4 H -1,4-diazocine and 4 H -1,4-oxazocine, and the nonaromatic nature of 1,4-dioxocine and foresee the aromaticity of the 1,5-compounds. The 1 H ,5 H -1,5-diazocine was thermally more stable than the 1 H ,4 H -1,4-diazocine. In the case of dioxocines and oxazocines the 1,4-species are more stable than the 1,5-species.