The Crystal Structure of Ethyl p-Azoxybenzoate

The low-temperature form (solid I) of the smectogenic compound ethyl p-azoxybenzoate (C18H18N2Os) is stable below 90 °C. The triclinic unit cell of space group P] and dimensions a = 7.56 + 0.02, b-- 18 35 + 0.07, c= 6.28 + 0.01 A, ¢¢= 94.38 ° + 0.30 °, ,8= 97.21 _+ 0.31 °, and y = 83.97 ° + 0.25 ° contains two molecules and has a calculated density of 1.325 g.cm-3. The observed density is 1.315 + 0.013 g.cm-3. Integrated intensities were measured at room temperature by a 20--~ scan on a four-circle diffractometer equipped with a post-diffraction monochromator and scintillation detector. The crystal structure was refined by full-matrix least-squares methods with 1460 independent reflections to a final R index of 0 093. The molecules are nearly planar (the normals to the planes of the two benzene rings diverge by only 0-5 °) and are packed in a parallel array, as contrasted with the imbricated structure which has been observed for several nematogenic crystalline solids. The carbonyl and nitroso oxygen atoms are all in the cis conformation, resulting in a large dipole component in the plane of the molecule and perpendicular to its long axis. It is speculated that this feature of the molecular structure may be characteristic of smectogenic compounds

The Crystal Structure of p-Azoxyanisole

The stable crystalline form ofp-azoxyanisole is assigned to space group P21/a (C~h) with four molecules in the unit cell having parameters a= 15-776, b= 8.112, e= 11-018 A and b\u27= 114 57 °. The crystal structure was refined by full-matrix least-squares to a final R value of 0.091 using 2507 reflections measured with a manually operated single-crystal diffractometer. The molecules are arranged in the unit cell with their long axes approximately perpendicular to the (100) plane. The angle between the normals to the two benzene rings is 22.6 °, and the -N=N- bond conformation departs from the planar trans position by approximately 4 2 °