In the pinacol rearrangement, a methyl group is found anti-periplanar to an activated alcohol functional group. This places the σ orbital of the methyl group parallel with the σ* orbital of the activated alcohol. Before the activated alcohol leaves as HO the methyl bonding orbital donates into the C–O antibonding orbital, weakening both bonds. This hyperconjugation facilitates the 1,2-methyl shift that occurs to remove water. See Figure 11 for the mechanism.