Dipole moments and molecular conformation of diazo-compounds. Part III. Benzoylphenyldiazomethane and related molecules

Abstract

Dipole moment and i.r. data on benzoylphenyldiazomethane may be interpreted either through the occurrence, in non-polar solvents, of cis–trans rotational isomerism at the diazo-carbonyl linkage, with the diazo-carbonyl group virtually planar, or through a single distorted structure with an azimuthal angle of ca. 85° between the planes containing the Bz and CPhN₂ groups. For o-chlorodiazoacetophenone both cis- and trans-diazo-carbonyl conformers occur; the presence of a trans-diazo-carbonyl conformer, as distinct from the cases of the meta- and para-derivatives, is attributed to phenyl rotation out of the diazo–carbonyl molecular plane, which releases the steric hindrance of the ortho-hydrogen atom. The presence of a single distorted arrangement of the chlorine and carbonyl groups is suggested. For m-chlorodiazoacetophenone only the diazo-carbonyl cis-conformer is present; the chlorine atom and the carbonyl group may be both cis and trans.