Characterisation of the conformational and tautomeric properties of benzylamino derivatives of 1,4-diphenyl-2-butene-1,4-dione using NMR spectroscopy

Abstract

The 1H and 13C NMR chemical shifts of substituted 1,4-dephenyl-2-butene-1,4-diones indicate that these compounds in CDCl 3 solution exist mainly in the s- trans-s- trans (Z) keto ( trans Z) configuration and that hydrogen bonding between the NH proton and the carbonyl group stabilize this conformer. However, in dmso-d 6 solution, both the s- trans-s- trans (Z) keto ( trans Z) and s- trans-s- cis (Z) keto ( cis Z) forms are present with the cis Z form dominating over the trans Z with a ratio of approximately 4:1. No enol form was detected for these compounds in these solutions. On this bases the presence of the cis keto (E) was eliminated because it is suggested that in going from the trans Z keto to the cis E keto form, an enol forms will be formed but this was not detected due to the fact that the rate constant of the trans to cis keto transformation is very fast.