Structural studies of N-(2′-substituted phenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboximides by X-ray diffraction and NMR spectroscopy—proofs for CH/π interactions in liquid and solid phases

Abstract

N-(2′-R-Phenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboximides with R = Me (1), OMe (2), OEt (3) and H (4) were investigated. The crystal and molecular structures of 1–3, determined by single crystal methods, show different conformations of the N-(2′-R-phenyl) group. Anti conformations and weak intermolecular CH/π contacts were found in 2 and 3, while anti and syn conformations coexist in 1 with CH/π contacts being absent. Solid-state 13C CP/MAS spectra confirm the X-ray molecular structural data. Two crystallographically independent molecules in the unit cell of 2 correspond to two isotropic chemical shifts for C atoms in the CP/MAS spectrum. The different molecular dynamics of both molecules in the crystal lattice of 2 indicated by the thermal factors and intermolecular CH/π contacts were clearly visible in different cross-polarisation profiles. The NMR data of 4 suggest that the phenyl ring bonded to the nitrogen is nearly coplanar to the ethanocarboximide ring. Full assignment of liquid state 1H and 13C NMR spectra of 1–4 was possible by application of high field NMR spectroscopy. Some incorrect assignments of 13C chemical shifts in the literature were revised. The different ratios of [syn]∶[anti] in solutions of chloroform and DMSO are explained in terms of different intermolecular CH/π interactions.