First Crystal Structure Analysis of an Aliphatic Carbocation—Stabilization of the 3,5,7‐Trimethyl‐1‐adamantyl Cation by CC Hyperconjugation

That hyperconjugation can result in extreme stabilization is confirmed by the first X-ray structure analysis of an aliphatic carbocation. Until now, only carbocations stabilized by π-electron systems or heteroatoms had been studied. The differences in bond lengths in the 3,5,7-trimethyladamantyl cation 1 (0.18(2) Å) are greater than those in compounds exhibiting the largest anomeric effects. 1′ is therefore the best description of the structure of the cation.