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

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/pi contacts were found in 2 and 3, while anti and syn conformations coexist in 1 with CH/pi contacts being absent. Solid-state C-13 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/pi 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 H-1 and C-13 NMR spectra of 1-4 was possible by application of high field NMR spectroscopy. Some incorrect assignments of C-13 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/pi interactions.