## Abstract

The molecular structure of dibenzyl has been determined to an accuracy of about 0$\cdot $01 A by using extensive X-ray data in three-dimensional Fourier syntheses to refine the approximate atomic parameters originally derived by Robertson. The three formally single-carbon bonds joining the benzene rings have lengths of 1$\cdot $50, 1$\cdot $48 and 1$\cdot $50 A and make angles of 115 degrees with each other. The departure from the standard length of 1$\cdot $54 A is discussed in relation to the analogous systems of polyisoprenes and 1$\cdot $5 dienes where related effects have been observed. The dimensions of the benzene rings also reflect the unusual character of the acyclic carbon bonds, two of the aromatic bond lengths being 1$\cdot $39 A and the other four 1$\cdot $37 A. The molecule, although possessing a centre of symmetry, is not absolutely symmetrical, since the central CH$_{2} \chembond{1,0} $ CH$_{2}$ bond is inclined at 70$\cdot $5 degrees to the plane of the benzene rings. This is ascribed to the influence of intermolecular forces.