Color and Conformation of Some Derivatives of Benzil in the Solid-State: Crystal-Structures of 2,2′-Dimethoxy- 4,4′-Dimethoxy- , 4-4′Diethoxy- and 4,4'-Dibenzyloxy-benzil

Abstract

The crystal structures of the colourless 2,2'-dimethoxybenzil (2) and 4,4'-diethoxybenzil (6), the yellow 4,4'-dimethoxybenzi (5), and the yellow polymorph of 4,4'-dibenzyloxybenzil (7) have been determined by single-crystal X-ray studies from diffractometer data at 295 K, and refined by full matrix least-squares techniques to residuals of 0.048 (1281 'observed' reflections), 0.041 (610), 0.052 (662) and 0.043 (2140) respectively. Crystals of 2,2′-dimethoxybenzil (2) are monoclinic, P2₁/c, a 7.861(4), b 7.991(2), c 21.557(9)Å, β90.37(4)º, Z 4. Crystals of 4,4'-dimethoxybenzil (6) are monoclinic C2/c, a 21.912(9), b 4.055(2), c 15.197(5) Å,β 102 13(3)º Z 4. Crystals of 4,4′-diethoxybenzil (6) are monoclinic C2₁/c, a 14.544(7), b 4.781(2), c 22.128(7), β 99.06(3)º, Z 4. Crystals of the yellow modification of 4,4'-dibenzyloxybenzil (7) are monoclinic P2₁/c, a 19.126(4), b 6.91 1(2), c 16.673(7) Å β 99.52(3)º, Z 4. It has been found that there is a correlation between the colour of the crystal and the conformation adopted by the molecule in the solid state with the colourless derivatives of benzil having the aromatic ring planes orthogonal.