Structures of vicinal polyketones

Abstract

The crystal structures of mesitil, dimesityl triketone, and dimesityl tetraketone have been determined by X-ray diffraction methods and refined by least squares techniques to residuals of 0.087, 0.070, 0.053, respectively. Crystals of mesitil are monoclinic, P2₁/n, a= 17.666(8), b= 6.232(3), c= 17.514(8)Å, β= 117.58(2)°, Z= 4. Crystals of dimesityl triketone are monoclinic, C2/c,a= 29.625(15), b= 9.329(5), c= 15.182(8)Å, β= 121.07(2)°, Z= 8. Crystals of dimesityl tetraketone are monoclinic, C2/c, a= 14.295(7), b= 8.411(4), c= 16.190(8)Å, β= 105.20(2)°, Z= 4. The two carbonyl groups of mesitil assume an s-trans conformation with the aromatic rings approximately perpendicular to the plane defined by the carbonyl groups. In contrast, the tri- and tetra-ketone had torsion angles >100° and of identical sign along the chain of carbonyl groups and torsion angles of 25–40° between aromatic rings and adjacent groups. The geometrical parameters of a series of open-chain di-, tri-, and tetra-ketones are compared.