Conformational studies of dihydrotetraphenylmethanes. 2. X-ray crystallographic and solution proton NMR studies of cis-1,4-dihydro-4-tritylbiphenyl and its 4'-bromo derivative: conformational control by an intramolecular edge-to-face aromatic interaction

摘要: X-ray structural studies of cis-1,4-dihydro-4-tritylbiphenyl (2a) and its 4'-bromo derivative 2b reveal that, in contrast with earlier predictions based on solution NMR data, both adopt a similar congested conformation which the cyclohera-1,4-diene ring is almost planar, forcing isolated aromatic into π-cloud one benzene rings trityl substituent leading to considerable stretching C 1 -C 11 bond close intramolecular edge-to-face interaction. Variable-temperature H experiments suggest that this interaction becomes increasingly important at low temperatures