The structure of acetyltriphenylsilane

Abstract

Crystals of acetyltriphenylsilane, Ph₃Si·COMe, are monoclinic, with a= 7·53, b= 28·7, c= 7·90 Å, β= 96°50′, Z= 4, and space group P2₁/c. The structure was determined with Mo-K_α scintillation counter data from Patterson and electron-density maps and refined by least-squares methods, to R 0·10 for 1669 observed reflexions.

The acetyl and three phenyl groups are arranged tetrahedrally around the silicon atom. The phenyl rings are oriented in a propeller fashion, the angle between the ring plane and the C(Ac)–Si–C(Ph) plane being about 60° for each of the rings. The mean aromatic C–C distance is 1·38₈Å, and the mean C–H length is 1·04 Å. Two distinct Si–C bond-lengths are found: Si–C(Ph), 1·864(σ 0·008), and Si–C(Ac) 1·926(σ 0·014)Å. This is similar to the situation found for the Ge–C bonds in acetyltriphenylgermane, and the difference in Si–C bond-lengths can similarly be explained on the basis of electronegativity differences.

The crystal structures of the silicon and germanium analogues, although not identical, have features in common. Both contain identical building units of two molecules related by a c glide plane, but the stacking of these units is different in the two crystals.