CONFORMATION OF OMEGA-FLUOROACETOPHENONE - AN NMR-STUDY USING A LIQUID-CRYSTALLINE SOLVENT

The proton NMR spectrum of a sample of omega-fluoroacetophenone dissol ved in a nematic liquid Crystalline solvent has been obtained and anal ysed to yield a set of 10 independent dipolar couplings. These have be en used to obtain a conformational distribution; P-LC(phi,psi), for th e bond rotational angles phi, which is for the C-CF bond, and psi, whi ch is for the ring-C bond. The distribution has a maximum at phi = 0 d egrees, which corresponds to a cis arrangement of the C-F and C-O bond s, and psi = 0 or 180 degrees, which refer to the C=O bond being in th e plane of the phenyl ring. There is a smaller peak in the distributio n at phi = 180 degrees, corresponding to the trans arrangement of the C-F and C=O bonds, and psi = 0 or 180 degrees. The barrier to rotation about the C-CE bond through phi depends strongly on psi, and vice ver sa.