Neutron diffraction study of aromatic hydrogen bonds: 5-ethynyl-5H-dibenzo[a,d]cyclohepten-5-ol at 20 K

摘要

The neutron diffraction crystal structure of the title compound, C17H12O, was determined at 20 K. One of the benzyl groups accepts intermolecular hydrogen bonds from a hydroxyl and an ethynyl group, one to each face of the ring. The bond donated by the hydroxyl group points almost linearly to an aromatic C atom with a H ... C separation of 2.339 (6) Angstrom. The bond donated by the ethynyl group points to the aromatic midpoint M with a H ... M separation of 2.587(5) Angstrom. The average acetylenic C-H bond length determined by low-temperature neutron diffraction is only 1.062(6) Angstrom, appreciably shorter than observed for chemicallydifferent C-H bonds.