Showing papers in "Acta Crystallographica in 1980"

Statistical dynamical theory of crystal diffraction. II. Intensity distribution and integrated intensity in the Laue case

Abstract: The theory described in the previous paper [Kato (1980). Acta Cryst. A36, 763-769] has been applied to calculating the intensity distribution in the topography of statistically homogeneous crystalline media. The integrated intensity for parallel-sided crystals is also presented. The formulae cover the whole range of crystal perfection. Primary and secondary extinctions can be treated on a unified theoretical base. A few numerical examples are given to demonstrate the variations of the integrated intensity as a function of the crystal thickness, the extinction distance and two parameters which characterize crystal perfection over short and long ranges compared with the extinction distance.

The Structures of N-Aromatic Amides: p-Aeetanisidide, N-2-Naphthylaeetamide and N-2-Fluorenylaeetamide

Abstract: The crystal structures of the N-aromatic amides p-acetanisidide [ N-(4-methoxyphenyl)acetamide] (AAS), N-2-naphthylacetamide (NAA) and N-2fluorenylacetamide (FAA) have been determined from visually estimated Cu Ka data, and refined to R values of 0.076, 0.075 and 0.061 for 1233, 1427 and 1023 non-zero reflexions respectively. The crystal data are: Pcab, a = 9.32 (1), b = 25.13 (2), c = 7.691 (5) A, z = 8 for AAS; Pcab, a = 9.651 (6), b = 28.23 (3), c = 7.518 (8) A, Z = 8 for NAA; and Cc, a = 16.77 (3), b = 4.830 (6), c = 15.85 (2) A, fl = 115.4 (1) °, z = 4 for FAA. The structures of AAS and NAA are homomorphous with that of acetanilide. The molecules related by a 2 t axis parallel to a are linked together by an N-H...O hydrogen bond to form a ribbon. The ribbons are held together by interactions between the aromatic rings related by a c glide. The dihedral angles between the rings are 75.3 ° for AAS and 54.0 ° for NAA, being close to those in benzene and naphthalene respectively. In FAA, the molecules related by a b translation are linked together by an N-H... O hydrogen bond to form a ribbon. The ribbon is stabilized by the parallel stacking of the aromatic rings. The morphotropism in the crystal structures of the N-aromatic amides is discussed in relation to the respective types of hydrogen bond.