Evidence of an n(amide) → π* Interaction in -Alkyl-,'-diacylhydrazines.

1,2-Dibenzoyl-1--butylhydrazine (RH-5849) and related -alkyl-,'-diacylhydrazines are environmentally benign insect growth regulators. Herein, we show that an unusual n(amide) → π* interaction mediated by a hydrazide amide nitrogen atom plays a crucial role in stabilizing their biologically active trans-cis (t-c) rotameric conformations. We provide NMR and IR spectroscopic evidence for the presence of these interactions, which is also supported by X-ray crystallographic and computational studies.