Conformation of ω-fluoroacetophenone: an NMR study using a liquid crystalline solvent

Abstract

The proton NMR spectrum of a sample of ω-fluoroacetophenone dissolved in a nematic liquid crystalline solvent has been obtained and analysed to yield a set of 10 independent dipolar couplings. These have been used to obtain a conformational distribution, P_LC(ϕ,ψ), for the bond rotational angles ϕ, which is for the C–CF bond, and ψ, which is for the ring–C bond. The distribution has a maximum at ϕ = 0°, which corresponds to a cis arrangement of the C–F and CO bonds, and ψ = 0 or 180°, which refer to the CO bond being in the plane of the phenyl ring. There is a smaller peak in the distribution at ϕ = 180°, corresponding to the trans arrangement of the C–F and CO bonds, and ψ = 0 or 180°. The barrier to rotation about the C–CF bond through ϕ depends strongly on ψ, and vice versa.