Chiral ureas with two electronegative substituents at 1‐N: An unusual case of coexisting pyramidal and almost planar 1‐N atoms in the same crystal

XRD studies of structure of N-acetoxy-N-methoxyurea and N,N-bis(methoxycarbonyl)-N-methoxyimide have revealed that in N-methoxy-N-X-ureas (X = OAc, Cl, OMe, N+C5H5) the additional shortening of NOMe bond took place, which arising from an nO(Me)-σ*NX anomeric orbital interaction. XRD studies of N-chloro-N-ethoxyurea crystal have revealed the presence of two kinds of anomeric nitrogen configuration in the ONCl group in the form of a pyramidal configuration and a planar configuration for same 1-N nitrogen atom. XRD studies of N-4-chlorobenzoyloxy-N-ethoxyurea have revealed that the degree of pyramidality of the 1-N nitrogen in N-aroyloxy-N-alkoxyureas is tuned by orientation of benzoyl group with respect to the NO bond, which in turn depends of size of N-alkoxy group. Chirality, 2009. © 2008 Wiley-Liss, Inc.