The single-crystal X-ray diffractometer installed at the PWA Laboratory in Frascati is described. The Huber four-circle goniometer is controlled by an IBM-compatible personal computer by means of a plug-in board interface based on the LSI chip Am9513. The program CS running under MS-DOS performs a wide variety of operations from random search to data collection. The angular resolution of the diffractometer is 0.0025 °, while the instrumental resolution at 8 keV, with an Si(lll) monochromator, is 0.0026 °. After preliminary tests, 2Zn insulin crystals were mounted on the diffractometer and reflections were measured using synchrotron radiation. The rocking curves show full widths at half-maxima (FWHM) in the range 0.013-0.031 ° mainly due to the mosaicity.

No abstract

Abstract A new X-ray diffraction study of p-nitroaniline shows that through-conjugation has highly significant effects on the geometry of the molecule, as compared to aniline and p-nitrobenzoic acid. The effects include a moderate decrease of the internal angles of the ring at substituted carbons, with respect to values derived by superimposing independent angular distortions from each substituent.

No abstract

The crystal structure of p-hydroxybenzoic acid monohydrate, CTH6Oa.H20, determined from photographic data [Fukuyama, Ohkura, Kashino & Haisa (1973). Bull. Chem. Soc. Jpn, 46,[804][805][806][807][808], has been refined to R = 0.0414 on 1454 counter reflexions. Crystals are monoclinic, space group P2~/a, with a = 17.752 (9), b = 6.442 (2), c = 6.731 (3) A, fl= 105.48 (6)°, Z=4. The benzene ring has approximate C2, (mm) symmetry and shows a slight quinoidal shortening of the central C-C bonds. The internal angles at the ipso positions of the ring are aon = 120.5 (1) °, acoon = 119.4 (1) °.