Anti-Anisaldehyde oxime

Abstract

CsH9NO2, M r = 151.17, orthorhombic, Pna2~, a -- 7.750(4), b = 11.572(1), c = 17.701 (1) A at 298 K, V = 1587.36 A 3, D x = 1.265 Mg m -3, Z = 8; R -- 0.077 for 719 reflexions. The (anti) configuration of the molecule is related to taste for the first time for oximes. Each molecule forms hydrogen bonds with two other molecules. The two molecules forming the independent asymmetric unit are nearly identical. Introduction. The title compound (AAO) was pre- pared according to standard organic-chemistry recipes (Vogel, 1961) and separated from the syn isomer by means of silica-column chromatography. Weissenberg photographs showed systematic absences consistent with the orthorhombic space group Pna2~. A thin eolourless needle was used to collect intensity data (Ni-filtered Cu Ka radiation, 2 = 1.5418 A) on a CAD-4 Enraf-Nonius automatic single-crystal diffractometer. Reflexions with 20 < 110 ° were scanned in the 09 mode; 1034 independent reflexions were collected and corrected for polarization and Lorentz factors. 315 of these reflexions having I < 3o(1) were not considered in the refinement. The structure was solved by means of the direct method using the program MULTAN (Germain, Main & Woolfson, 1971) included in the Enraf-Nonius struc- ture determination package (SDP) for a PDP-11 computer. The Fourier map, calculated with the set of phases presenting the highest combined figure of merit given by MULTAN, revealed all the non-hydrogen atoms except for one N and one O of one of the two molecules of the independent unit; no H atoms were found. Refinement was achieved by least-squares procedures for all except the H atoms; for these, positions were calculated stereochemically and iso- tropic thermal factors equal to those of the carrier atoms were assigned. These parameters were kept fixed in the refinement. The refinement with weights w = 1/a(Fo) 2 was ended when the maximum shifts in the atomic coordinates and isotropic thermal factors were less than ) and ) of the corresponding standard deviations respectively. The final R value is 0.077. The number of independent reflexions does not justify further refinement with anisotropic thermal factors but