The Central Bond Length in 1,2-Diarylethanes

The structures of several vicinal diarylethanes are determined by X-ray crystallography and calculated by Hartree-Fock ab initio computations. The structure of the general class of 1,2-diarylethanes is discussed, and a “standard molecular fragment” is derived from a search of the Cambridge Structural Database. The anomalously short C_sp³-C_sp³ (central) bond reported for the parent 1,2-diphenylethane and some derivatives is not representative of the average molecular geometry derived from the database and is likely an experimental artifact. High-level split valence ab initio calculations predict a normal (1.54 Å) bond length for C_2h1,2-diphenylethane.