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 + C 5 H 5 ) the additional shortening of NOMe bond took place, which arising from an n O(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.