Conformation of 1-(2-bromophenyl)azetidin-2-one and 1-(2-bromophenyl)pyrrolidin-2-one

Abstract

U.v. data suggest that 1-(2-bromophenyl)pyrrolidin-2-one (2a) is substantially non-planar in solution while the related 1-(2-bromophenyl)azetidin-2-one (1a) is planar. Crystal structure studies of these two compounds show this effect exists in the solid also and that there is a 72° dihedral angle between normals to the phenyl and fivemembered rings in the γ-lactam (2a), while the rings in the β-lactam (1a) are coplanar. Compound (1a) crystallizes in space group C2/c with cell dimensions a= 15.91 (1), b= 7.70(1), c= 14.48(1)Å, β= 103.84(1)° while compound (2a) crystallizes in space group P2₁/c with a=10.55(1), b= 6.83(1), c= 15.41(1)Å, β= 112.02°(2). Both structures were solved by heavy atom methods.