Conformational study on some β-phenyl-α,β-unsaturated ketones

The conformation of three (E)-β-phenyl-α,β-unsaturated ketones and their corresponding (Z)-isomers 1, 2, and 3 was established by IR and ASIS. (Z)-1 and (E)-1 have exclusively the s-trans conformation. The two isomers of 2 occur in both conformations but there is a higher s-cis to s -trans ratio with the (Z) than with the (E)-isomer. (Z)-3 appears to exist exclusively in the s-cis conformation, the (E)-isomer has a small content of the s-trans conformation. It was concluded that the ASIS for H_b, is a measure of the s-cis content of the conformational equilibrium.