Conformation of non‐aromatic ring compounds ‐ 84 Dipole moments and 100 MHz Fourier‐transform Proton Magnetic Resonance spectra of some substituted 3‐phenylglutaric anhydrides; a conformational analysis

The dipole moments and PMR spectra of a series of 3-(p-X-phenyl)glutaric anhydrides [X: H (2), F (3), Cl (4), Br (5), NO2 (6)] and of 3-(p-chlorophenyl)-3-methylglutaric anhydride (7) were measured and interpreted in terms of conformational properties of the anhydride ring and its side-chain. The dipole moments of 2-7 (measured in benzene) were 4.73, 3.82, 3.66, 3.70, 2.53 and 4.59 Debyes, respectively. Theoretical dipole moments for the individual conformers were calculated from atomic coordinates of model structures and standard point charges. The equilibrium compositions derived from vicinal proton coupling constants are compared with those obtained from the dipole moments. A satisfactory agreement is noted. The p-X-C6H4 group in 2-6 is shown to prefer the equatorial Epl conformation (Ph//βH) over the axial Apr conformation (Ph // βH) to the extent of 0.6-1.2 kcal/mol. In compound 7 the equatorial Ph group probably takes up the Epr conformation.