Relayed Proton Brake in -Pyridyl-2--propylaniline Derivative: Two Brakes with One Proton.

The addition of methanesulfonic acid to -(2,6-dimethylpyridin-4-yl)--methyl-2--propylaniline led to the selective protonation of the pyridine nitrogen atom, resulting in a significant deceleration of the rotation rates around both -pyridyl and -(-Pr)phenyl bonds through a relayed brake mechanism.