Stereodynamics of Bond Rotation in Tertiary Aromatic Amides

The degree to which the rotations about the C−N and Ar−CO bonds of aromatic amides occur in a concerted manner was investigated by a variety of NMR and kinetic techniques. Otherwise complex kinetic analyses were simplified by exploiting symmetry and asymmetry in the N‐substituents of amides. In 2‐unsubstituted 1‐naphthamides bearing branched N‐substituents, most conformational changes about the amide group were by correlated rotation, though uncorrelated Ar−CO rotation also occurred to some extent. In 2‐substituted 1‐naphthamides, correlated rotation accounted for all of the Ar−CO rotations, though a significant amount of uncorrelated C−N rotation also occurred. Naphthamides bearing branched N‐substituents thus turn out to be efficient molecular gears: Compound 12 showed almost no gear slippage. A “cogwheeled” rotation about the Ar−CO and C−N bonds can be observed for tertiary aromatic amides (see scheme). The degree to which the rotations occur in a concerted manner was investigated by a variety of NMR and kinetic techniques. Otherwise complex kinetic analyses were simplified by exploiting symmetry and asymmetry in the N‐substituents of amides.