First X-ray Crystallographic Study of a Benzyl Cation, Cumyl Hexafluoroantimonate(V), and Structural Implications

Abstract

The crystal structure of the cumyl cation (1; 2-phenyl-2-propyl cation) has been determined at −124 °C (as hexafluoroantimonate, 1·SbF6; R1 = 0.0502, wR2 = 0.1054). The cation 1 is nearly planar and has a short C+−Cipso bond (1.41(2) A) and bond lengths in the phenyl ring which agree with strong benzylic delocalization. The weak but distinct shortening of the C+−CH3 bonds by 0.025(12) A indicates weak C−H hyperconjugation. Nearly all H atoms are involved in H···F contacts to SbF6 anions, and one close C+···F contact (3.11(2) A) is observed. The phenyl rings form infinite stacks and are shifted against each other in the stack.