Effect of methyl substitution on the crystal structures of complexes of quinones with hydroquinones. Crystal structures of the 1 : 1 complex of 2,3,5,6-tetramethyl-1,4-benzoquinone with 2,3,5,6-tetramethylbenzohydroquinone and of the 1 : 2 complex of 2,3,5,6-tetramethylbenzoquinone with hydroquinone. Correlation of Fourier transform infrared spectra with structure

Abstract

The crystal structures of the 1 : 1 complex of 2,3,5,6-tetramethyl-1,4-benzoquinone with 2,3,5,6-tetramethyl-1,4-hydroquinone (duroquinhydrone), and of the 1 : 2 complex of 2,3,5,6-tetramethyl-1,4-benzoquinone with hydroquinone have been determined by X-ray methods. The structure of duroquinhydrone (C₁₀H₁₂O₂·C₁₀H₁₄O₂) is monoclinic, space group P2₁/c with a= 8.006(2), b= 6.574 6(8), c= 17.056(4)Å, β= 105.02(2)°, Z= 2. It was solved by direct methods and refined to R= 0.048 for the 994 non-zero reflections recorded. The gross features of the structure are remarkably similar to those of monoclinic quinhydrone. The structure of the 1 : 2 complex of tetramethylbenzoquinone with hydroquinone is triclinic, space group P with a= 7.578(2), b= 9.455(3), c= 7.183(2)Å, α= 94.02(2), β= 107.75(2), γ= 88.59(2)°. There is one 1 : 2 complex in the unit cell, with each of the three component molecules occupying a crystallographic centre of symmetry. The structure has been refined to an R-factor of 0.046 on 1 634 non-zero reflections. There are chains of alternating quinone and hydroquinone molecules with the other hydroquinone molecule lying between the chains. The structure is unusual in comparison with other complexes between quinones and hydroquinones in that the typical two-dimensional layers of molecules held together in one direction by hydrogen-bonding chains of nearly coplanar quinones and hydroquinones and in the other by π-complexing of overlapping quinone and hydroquinone molecules are absent in this crystal.

These structures, together with structures of other quinone–hydroquinone complexes recently reported, suggest generalizations which help to explain the stoicheiometry of such complex formation.

The implications for the Fourier transform i.r. spectra of the hydrogen bonding of quinone–hydroquinone complexes are discussed.