Structure-reactivity correlations, crystals

Ionic chiral auxiliaries Crystal structure-reactivity correlations... 

Both P-phenyl quenching and a-cleavage for the o,a -diaryl ketones in solution are known to occur within sub-nanosecond time scales. The results with crystals of cis- and tram-Si are consistent with their molecular structures and add confidence to the use of structure-reactivity correlations known from solution to reactions occurring in crystalline soUds. 

Crystal Structure-Reactivity Correlations for the cis-9-Decalyl Aryl Ketone System... 

Fu, T.Y., Scheffer, J. R., and Trotter, J., Crystal structure-reactivity correlations in the solid state photochemistry of N-(tert-butyl)succinimide, Can. J. Chem., 72, 1952, 1994. 

Vishnumurthy, K., Guru Row, T. N., and Venkatesan, K., Studies in crystal engineering crystal packing, topological photodimerization and structure-reactivity correlations in fluoro-substituted styrylcoumarins, /. Chem. Soc., Perkin Trans. 2, 615-619,1997. 

The theoretical results described here give only a zeroth-order description of the electronic structures of iron bearing clay minerals. These results correlate well, however, with the experimentally determined optical spectra and photochemical reactivities of these minerals. Still, we would like to go beyond the simple approach presented here and perform molecular orbital calculations (using the Xo-Scattered wave or Discrete Variational method) which address the electronic structures of much larger clusters. Clusters which accomodate several unit cells of the crystal would be of great interest since the results would be a very close approximation to the full band structure of the crystal. The results of such calculations may allow us to address several major problems ... 

For a partieular phase type, the magnitude of the observed effects on reactivity correlates with the structural compatibility of the solute and solvent, to a first approximation. Since liquid crystals are expected to favour specific orientations or conformations of reactants, reactions involving solutes, transition states or products that are most closely related structurally to the liquid crystalline solvent often show the largest effect. However, examples also exist where the reactivity of small solutes that are not solvent-like, or of solutes whose reaction involves only minor changes in shape, is significantly altered in a liquid crystalline solvent. This is... 

In many respects, the present results resemble the pioneering work of the late G. M. J. Schmidt and his co-workers at the Weizmann Institute of Science, who used crystal structure-solid-state reactivity correlations to elucidate the geometric requirements for intermolecular [2+2]-photocycloaddition. In both his case and ours, distance and angular requirements for reaction were established and the structure and stereochemistry of the products were shown to be simply and directly related to the molecular structure existing in the bulk crystal. 

A new photoactive monoclinic polymorph of 6-(2, 4 -dinitrobenzyl)-2,2 -bipyri-dine was obtained from an acetone/methanol solution, and the structure compared to the previously known photoactive orthorhombic and photoinactive monoclinic forms [94]. Correlation of these structures with those of related nitrobenzylpyridines was used to understand the relationships existing between structure and photochro-mism. The comparison of the reaction cavities around the reactive pyridyl-benzyl-nitro fragment indicated that photochromic activity required rotational freedom of the ortho-nitro group in the crystal and its accessibility from the proton-donor and proton-acceptor sites. 

The major effect of new advanced techniques on catalyst structure is found in zeolite catalysis. NMR techniques, especially MASNMR, have helped to explain aluminum distribution in zeolites and to increase our understanding of critical parameters in zeolite synthesis and crystallization. MASNMR, combined with TEM, STEM, XPS, and diagnostic catalytic reaction probes, has advanced our knowledge of the critical relationship between the structure and reactivity patterns of zeolites in the chemical fuels industry. Throughout the symposium upon which this book is based, many correlations were evident between theoretical quantum mechanical calculations and the structures elucidated by these techniques. 

Crystal structure correlations explore relationships between reactivity and actual structural parameters such as bond lengths and angles. Reactivity measured in terms of rate and equilibrium constants allows us to introduce the energy dimension directly, because these constants translate directly into... 

In an early attempt to correlate reactivity and structure Guy et al. (1977) compared the crystal structure of the steroidal ketone [56] with those of related compounds. The regioselectivity and rapid rate of the base-catalysed... 

There are no known exceptions to rule 2, though many fewer data are available. The sensitivity parameter is by definition obtainable only where the linear bond length-reactivity relationship is observed, so exceptions are in any case less likely. It is not readily accessible — for accurate definition it requires good quality structures for a series of at least four to five derivatives — so any use outside the area of crystal-structure correlation is likely to be limited to situations where a particularly important question of mechanism or reactivity cannot be resolved by conventional approaches.21... 

This section considers recent attempts to extrapolate from observed structures to the experimentally unattainable transition state structures for bond making and breaking reactions. (Transition state structures for conformational changes are experimentally observable in the crystal in favourable cases, as described in Section 3, pages 135-136.) The approach builds on the regular correlations between structure and reactivity, particularly the linear correlations with bond length described in the previous section. 

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