CONFORMATIONAL-ANALYSIS OF ROTATIONAL BARRIERS IN N-ARYLPYRROLIDIN-2-ONES

The structures of N-phenylpyrrolidin-2-one and the three isomeric N-tolylpyrrolidin-2-ones have been studied by single-crystal X-ray diffraction, as a basis for the conformational analysis of the barrier to rotation around the single bond between the rings. Force-field simulation of the molecular structure is consistent with a rotational barrier of 7 kJ mol-1. Crystal data: N-phenylpyrrolidin-2-one, orthorhombic, Pbca, a = 14.114 (3), b = 6.879 (4), c = 17.386 (5) angstrom, R = 0.059 for 1110 unique reflections [F(o) greater-than-or-equal-to 4-sigma-(F(o))]; N-(2-methylphenyl)pyrrolidin-2-one, orthorhombic, Pbca, a = 16.999 (4), b = 16.411 (2), c = 7.008 (2) angstrom, R = 0.077 for 1479 unique reflections [F(o) greater-than-or-equal-to 4-sigma-(F(o))]; N-(3-methylphenyl)pyrrolidin-2-one, monoclinic, P2(1)/c, a = 10.411 (2), b = 7.645 (2), c = 12.782 (1) angstrom, beta = 110.32 (1)-degrees, R = 0.065 for 1641 unique reflections [F(o) greater-than-or-equal-to 4-sigma-(F(o))]; N-(4-methylphenyl)pyrrolidin-2-one, orthorhombic, P2(1)2(1)2(1), a = 7.668 (2), b = 10.804 (2), c = 11.456 (1) angstrom, R = 0.054 for 1155 unique reflections [F(o) greater-than-or-equal-to 4-sigma-(F(o))].