Spectral correlations for β-chlorovinyl ketones

The IR and UV spectroscopic data of a series of alkyl substituted β-chlorovinyl ketones have been determined. Some of the IR and UV spectroscopic criteria, developed for the S-cis or S-trans conformation of ordinary α,β-unsaturated ketones, seem to be applicable for the β-chlorovinyl ketones: the S-cis conformer shows a low ratio (rⁱ) of the integrated intensities of the carbonyl and double bond stretching vibrations and a relatively low UV ε value; whereas high rⁱ and ε values are found for the S-trans conformer; non-planarity increases the rⁱ value and decreases the ε value.The prefered conformations as determined by the IR and UV spectral data have led to the presentation of benzene solvation models for a series of β-chlorovinyl ketones. These models made it possible to assign thecis ortrans structure to α,β-dialkyl-β-chlorovinyl ketones on the basis of the NMR aromatic solvent induced shifts of the β-alkyl group: high solvent shifts to a higher field (0·31–0·66 ppm) are found forcis-β-chlorovinyl ketones, whereas low solvent shifts (0·040·15) are found for thetrans-β-chlorovinyl ketones. Assignments based on the chemical shifts alone can lead to erroneous interpretations.