D. A. Evans. B. Breit Carbocations: Structure Chem 206 Carbocation Stabilization Through Hyperconjugation Physical Evidence for Hyperconjugation: The Adamantyl Cation pating in the hyperconjugative interaction, e. g C-R, will be lengthened while the C(+)C bond will be shortened First X-ray Structure of an Aliphatic Carbocation ■ FMO Description 1431A Take linear combination of o C-R(filled) and C prorbital (empty FsSb-F-SbFsI F*C-R C-R 10061608A T. Laube, Angew. Chem. Int. Ed. 1986, 25, 349 aC-R gC-R + planar orientation between interacting orbital C-H versus C-C Hyperconjugation The Adamantane Reference The t-Pentyl Cation alculated carbocation (MM-2 agrees with solution 1528A Me 110 1582A 1092A A Stable Carbocation Chemistry, 1997. p 46-47C C Me H H Me Me Me Me Me H C H H C H H Me Me Me C [F5Sb–F–SbF5] – C H H C H C C R H H H H R D. A. Evans, B. Breit Chem 206 Take linear combination of s C–R (filled) and C pz -orbital (empty): s C–R + s* C–R s C–R s* C–R + Syn-planar orientation between interacting orbitals ■ FMO Description E + + Carbocation Stabilization Through Hyperconjugation C–H versus C–C Hyperconjugation: The t-Pentyl Cation + 1.582 Å + 1.107 Å 1.092 Å R. P von Schleyer in Stable Carbocation Chemistry, 1997, p 46-47 Calculated carbocation agrees with solution structure Physical Evidence for Hyperconjugation: The Adamantyl Cation T. Laube, Angew. Chem. Int. Ed. 1986, 25, 349 First X-ray Structure of an Aliphatic Carbocation 100.6 ° 1.608 Å 1.431 Å + Bonds participating in the hyperconjugative interaction, e.g C–R, will be lengthened while the C(+)–C bond will be shortened. The Adamantane Reference (MM-2) 110 ° 1.530 Å 1.528 Å + Carbocations: Structure