Aliphatic C-H/π and Heteroatom/π Interactions in N-Aryl-3,4-(9′,10′-dihydroanthracene-9′,10′-diyl)succinimides

A series of N-aryl-3,4-(9',10'-dihydroanthracene-9',10'-diyl)-succinimides have been synthesized as model compounds to study the interaction of an aromatic pi system with aliphatic H atoms and heteroatoms such as oxygen, sulfur, and fluorine. The steric requirements of the rigid scaffold forces the N-aryl residue and a benzene ring of the dihydroanthracenyl moiety to adopt an edge-to-face conformation in which one of the ortho-substituents of the N-aryl group interacts with the pi system. The succinimides were generally obtained as mixtures of isomers and their ratios were considered as a function of the substitution pattern at the ortho positions of the N-aryl residue. The experimentally observed ratios were in good agreement with those predicted computationally by DFT calculations at the BMK/cc-pVDZ level of theory. From this study it was concluded that in these systems the aliphatic C-H/pi interaction is mildly stabilizing and, to a certain extent, capable of overcoming unfavorable steric effects. On the other hand, the interaction of a pi system with oxygen, sulfur, or fluorine atoms was destabilizing. When methyl or ethyl groups were allowed to compete with oxygen and fluorine for interaction with the benzene ring, C-H/pi interactions were consistently observed to preferentially occur despite unfavorable steric effects.