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

The crystal structure of the cumyl cation ( 1; 2-phenyl-2-propyl cation) has been determined at −124 °C (as hexafluoroantimonate, 1 ·SbF 6; R 1 = 0.0502, wR 2 = 0.1054). The cation 1 is nearly planar and has a short C + −C ipso bond (1.41(2) Å) and bond lengths in the phenyl ring which agree with strong benzylic delocalization. The weak but distinct shortening of the C + −CH 3 bonds by 0.025(12) Å indicates weak C−H hyperconjugation. Nearly all H atoms are involved in H···F contacts to SbF 6 anions, and one close C + ···F contact (3.11(2) Å) is observed. The phenyl rings form infinite stacks and are shifted against each other in the stack.