Conformational studies by nuclear magnetic resonance. Part I. The barrier to hindered rotation in 4-dimethylaminobut-3-en-2-one around the C–C single bond

Abstract

The free energy of activation and other thermodynamic parameters of hindered rotation around the C(2)–C(3) bond in 4-dimethylaminobut-3-en-2-one have been established; ΔG*_{s-cis→s-trans}= 11·5 ± 0·2 kcal mol^–1; ΔG*_{s-trans→s-cis}= 11·1 ± 0·2 kcal mol^–1. The low value of free energy of isomerisation, ΔG°= 0·4 kcal mol^–1 appears to indicate that the s-trans form is non-planar. Divergences between the relative value of the barrier to C–C and C–N and the estimated bond orders are emphasized.