Unusual π−π cofacial parallel stacked geometry interaction and intramolecular Csp2-H···O=C bonding in 3-Aryl-5-propylene-3-pyrrolin-2-one molecular structure

Abstract

The title compound was synthesized by hydrocyanation of 1-phenyl-hex-1-yn-3-one using the Ni(CN)2/CO/KCN system in an alkaline aqueous medium under mild conditions, a crystal of the mentioned compound was obtained for single-crystal X-ray diffraction studies. The structure consists of a pyrrolinone ring (N1C2C3C4C5) and a phenyl ring (C6C7C8C9C10C11) linked by a C6-C3 bond. Both planar rings describe a torsion defined by the angle C11-C6-C3-C4 (15.7 °), showing an unexpected quasi-planar conformation. The CH···O bonding, the homoconjugation between double bonds in the phenyl and pyrrolinone rings, and the exocyclic double bond stabilize this conformation. Unexpectedly, interaction π−π cofacial parallel stacked is present in the crystal structure between the unsubstituted aromatic rings. The geometry of the molecular structure was calculated at the DFT-B3LYP-D3/6–31+G** level of theory supporting the quasi-planar conformation, the CH···O bonding, and the homoconjugation between double bonds in phenyl and pyrrolinone rings. Furthermore, to support the X-ray diffraction findings noted above, experimental and theoretical NMR studies were performed. The 1H and 13C chemical shifts calculated by Ochsenfeld theoretical method at the ωB97X-V/6–311+G(2DF,2P)[6–311G*]//ωB97X-D/6–31G* level are reported here. Thus, the features of the bond between the phenyl group and the quaternary carbon adjacent to the methine proton at high downfield (7.09 ppm) indicate a quasi-planar conformation between the phenyl and pyrrolinone rings.