H-1 AND C-13 NMR SPECTRAL AND X-RAY CRYSTALLOGRAPHIC STUDY OF 3-METHYL-2,4-DIPHENYLQUINOLINE - STERICALLY HINDERED PHENYL GROUPS AND THE PSEUDO-PERI-PROXIMITY EFFECT

A study of the rotation of the sterically hindered phenyl groups in 3- methyl-2,4-diphenylquinoline by H-1 and C-13 NMR spectroscopy, support ed by CP-MAR solid state NMR measurements and X-ray crystallography is presented. The 53-degrees dihedral angle of the C6H5-2 ring results i n a reduced electrostatic field effect and a residual 'pseudo-peri pro ximity' effect is proposed to operate. The rotation of the C6H5-4 ring to a near orthogonal position causes anisotropic shielding effects at 5-H and the ortho-protons. The NMR spectral assignments are supported by 2D studies and the results have been compared with the unhindered compound, 2,4-diphenylquinoline.