Direct Evidence for Synchronicity between Rotation along Cα−C′ and Pyramidalization of C′ in Amides.

In amides, the presence of sinusoidal synchronicity between rotational motion along Cα−C′ σ‐bond (τ rotation) and the concomitant pyramidalization of C′ (θ) is evidenced for the first time in solution. Temperature‐dependent 1H NMR and DFT simulations on suitable amide models (iBui−−Proi−Xaai+1−OMe; iBu is isobutyryl) reveal the perturbation in synchronicity when τ‐rotation is 'locked' with interactions, resulting in a strain on the amide bond, which influences a decrease in energy barrier for the amide bond cis/trans isomerism by ∼1.68 kcal/mol. [ABSTRACT FROM AUTHOR]