Aromaticity of 15,16-dimethyldihydropyrene relative to benzene and strain energies of elusive [e]-fused bis-dimethyldihydropyrenes

摘要

Density functional theory calculations have been performed to quantify the aromaticity of 15,16-dimethyldihydropyrene relative to benzene through the dimethyldihydropyrene probe. Moreover, the strain energies in [e]-fused bis dihydropyrenes 6a-d are also calculated by comparison with a suitable reference system. The geometric analysis reveals that all isomers of the bis dihydropyrene 6 (6a-d) are strained, and the strain energies range from 5.87-11.31 kcal mol(-1). The dihydropyrenes 6b and 6d show only splitting type distortion (S-) whereas 6a and 6c have additional arching type distortion (A-) which results in higher strain energies for 6a and 6c. A planar non-strained analog 7 has been proposed, and investigated to elucidate the aromaticity of dimethyldihydropyrene relative to benzene, through magnetic (H-1 NMR and NICS) and geometric (bond fixation) criteria. The aromaticity of the dimethyldihydropyrene is estimated comparable to benzene. Moreover, magnetic and geometric parameters of 6a-d are also discussed within the context of their inability to estimate the aromaticity of dimethyldihydropyrene. (C) 2015 Elsevier B.V. All rights reserved.