Synthesis, Characterization, and Conformational Study of Acylhydrazones of α,β‐Unsaturated Aldehydes

ABSTRACT New acylhydrazone derivatives 1–6 have been synthesized by condensation of tert‐butylphenoxyhydrazide and cinnamaldehyde A or β‐chloro‐α,β‐unsaturated aldehydes B–F . They were characterized by IR, ( 1 H, 13 C, 19 F) nuclear magnetic resonance (NMR), and high‐resolution mass spectroscopy. The NMR data show the existence of the cis / trans ‐amide conformers due to N–C(O) bond rotation in addition to the E / Z isomers around the C=C bond of some of the starting aldehydes. The solvent polarity effects on the ratios of the cis / trans ‐amide rotamers have also been investigated. Importantly, rotational barriers around the N–C(O) bond for all compounds 1–6 (62.9–68.8 kJ mol –1 ) were calculated using the coalescence‐temperature method according to the Eyring equation. The results are discussed and compared with those previously reported for related acylhydrazones of aryl adehydes and acetone.