Folded conformations ofN-(aminoalkyl)-9-phenanthrenecarboxamides in the crystal and solution

Abstract

The molecular structures of three tertiary N-(aminoalkyl)-9-phenanthrenecarboxamides were investigated in solution and the solid state by means of 1H NMR spectroscopy and x-ray crystallography. The tertiary amides exist as a mixture of E and Z isomers in solution and the aminoalkyl groups exist as a mixture extended and folded conformers. A crystalline N-(aminoethyl)amide was obtained as the pure Z isomer in which the phenanthrene and amide planes are nearly perpendicular and the aminoethyl group is folded over the less hindered face of the amide group. Rotation about the Ar–C(O) bond is slow in resolution rendering these molecules chiral on the NMR time-scale. As a consequence, the α-methylene protons display large diasterotopic splittings when the aminoalkyl group is syn to the amide carbonyl. Folded conformations place the Z and E aminoalkyl groups in the deshielding and shielding regions, respectively, of the phenanthrene rings, resulting in large differences in chemical shifts. © 1997 John Wiley & Sons, Ltd.