Structural analysis of internally crowded naphthalene derivatives. peri-diphenylacenaphthene

Abstract

The sterically crowded peri-diphenylacenaphthene (1) has been synthesized by an aryl-aryl coupling reaction, and its conformation in the crystal determined by x-ray diffraction. The strain induced by nonbonded interactions between the phenyl groups greatly affects the geometry of the molecule as a whole. The phenyl rings are face to face, making an angle of 57" to the naphthalene plane, and are splayed apart. The phenyl to naphthalene bonds are nearly identical in length with the interannular bonds of biphenyl and p-terphenyl, in which the aromatic rings are coplanar. A comparison is made of the structures of 1,8-diphenylnaphthalene, peri-diphenylacenaphthene, and 1,4,5,8-tetraphenylnaphthalene, which constitute a homologous series of peri-phenylnaphthalenes differing only in the arrangement of groups at one end of the molecule. Substantial deformations of angles and bond lengths in the naphthalene framework of these compounds are analyzed in terms of force vectors acting throughout the bonding skeleton. This analysis helps to explain the surprising ease of rotation about the interannular C-C bonds in these compounds. The ^1H NMR spectrum of 1 indicates that the preferred conformation in solution is analogous to that in the crystal.