D D MacNicol | PubMed Health

PubMed2001

A comparison of 2,7-dihydro-2,2,7,7-tetramethyl-3,6-diphenyl-1,4,5-thiadiazepine and the corresponding 1,1-dioxide.

The structures of the highly substituted title heterocycles, C(20)H(22)N(2)S and C(20)H(22)N(2)O(2)S, have been determined at 123 (1) K. Both molecules possess exact C(2) symmetry and the seven-membered rings have very similar twist-boat conformations. The magnitudes of the C-S-C bond angles, 107.13 (6) and 108.27 (7) degrees, respectively, are influenced significantly by the four substituent methyl groups on the seven-membered rings.

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PubMed2000

Charge densities from high-resolution synchrotron X-ray diffraction experiments.

The combination of intense X-ray sources, especially synchrotron radiation, with area-detector technology has accomplished an enormous advance in the experimental conditions available for charge-density analysis by single-crystal high-resolution X-ray diffraction. Such experiments can now be carried out in a time measured in hours rather than weeks. Some features of these experiments are examined and preliminary results are reported for charge-density studies of 2-hydroxy-5-nitrobenzaldehyde N-cyclohexylimine (1), octakis(m-tolylthio)naphthalene (2), and 7-fluoro-4-styrylcoumarin (3). Weak interactions in crystals of (1) and (3) are found to have similar charge-density characteristics. Cages in the crystal lattice of (2) have a complex charge distribution.

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