Pyridine–acetaldehyde, a molecular balance to explore the n→π*interaction

Abstract

The complex pyridine–acetaldehyde is formed through an n->pi* interaction and a C‐H∙∙∙O contact. The acetaldehyde methyl group internal rotation induces a phase‐locked intermolecular oscillation along the Bürgi‐Dunitz coordinate. Surprisingly, this sort of molecular balance extracts energy through the n->pi* interaction to reduce the size of the internal rotation barrier.