Chemistry of Anthracene–Acetylene Oligomers. XXIV. Theoretical Evaluation of Molecular Strain and Interactions in Anthracene–Acetylene Cyclic Oligomers by Homodesmotic Reaction Method

Abstract

Abstract The structures and stabilities of 1,8-anthrylene cyclic oligomers having acetylene or diacetylene linkers were investigated by DFT calculations with M05 and M06 series functionals. The structures of the cyclic oligomers were reasonably reproduced at the M05-2X/6-31G* level by using the interlayer distance between stacking anthracene planes in the anthracene–acetylene cyclic tetramer as benchmark. The structural features of the cyclic oligomers ranging from dimers to hexamers were discussed on the basis of the optimized structures. The stabilities of the cyclic oligomers were analyzed by thermochemical calculations of the homodesmotic reactions. The decreased stabilities of the odd-numbered oligomers are mainly attributable to molecular strain due to bending deformations at acetylene carbons. The increased stabilities of the tetramers and the hexamers are attributable to the intramolecular π···π interactions between anthracene units. The contributions of other factors influencing the overall stability, such as conjugation, steric hindrance, aromaticity, and CH···π interaction, are also discussed.