Organic crystal photochemistry

ONP may be used to enhance the nuclear spin polarization of bulk organic crystals by several orders of magnitude. While ONP has been performed in such materials utilizing a variety of related approaches, to date its application has been limited to fundamental investigations of the structure, dynamics, photochemistry, and photophysics of the organic crystalline substances themselves. However, recent results - including the demonstrations of very high polarizations in proton spins under relatively mild conditions, as well as the observation of ONP in polycrystalline materials - bodes well for expansion of the application of these approaches to other fields. 

J. R. Scheffer, P. R. Pokkuluri, Unimolecular photoreactions of organic crystals the medium is the message, in Photochemistry in Organized and Constrained Media, ed. V. Ramamurthy, VCH Verlag GmbH, Weinheim, 1991, pp. 185-246. 

In this chapter the topochemical [2+2] photoreactions of diolefin crystals are reviewed from the viewpoints of organic photochemistry, analysis of reaction mechanism, and crystallography as well as in terms of synthetic polymer chemistry and polymer physics. 

L. Lahav, M. Probing reaction pathways via asymmetric transformations in third and centro-symmetric crystals in Photochemistry in Organized and Constrained Media Ramamurthy, V., Ed. VCH Publishers New York, New York, 1991, pp 248-302. 

Single crystal-to-single crystal reactions are quite rare in solid-state organic photochemistry, and we were fortunate to discover a second example in the Yang photocyclization of the 1-phenylethylamine salt of 2-methyl-2-benzoyl-p-carboxylic acid 39 [37]. 

The examples of ex situ steady-state X-ray photodiffraction utihzed to follow the photodimerizations of olefin bonds in a single-crystal-to-single-crystal (or nearly so) manner are ubiquitous in the chemical literature. The interest of sohd-state chemists in this reaction dates back to the work of Cohen and Schmidt [30, 31], and it has become much of a guinea pig in organic solid-state photochemistry. In 1993, Enkelmann and collaborators published two seminal papers in the Journal of the American Chemical Society [32] and in Angewandte Chemie [33], where they presented a series of structures of a-tra s-cinnamic acid crystals reacted to various extents. These reports laid the way for a plethora of later studies on the olefin photodimerization reaction. The convenience of the high conversion and the simple mechanism, combined with the relatively small structural perturbation that it requires, has turned this reaction into a very useful tool to probe intermolecular... 

Vaida, M., Popovitz-Biro, R., Leiserowitz, L., and Lahav, M. (1991). Probing reaction pathways via asymmetric transformations in chiral and centrosymmetric crystals. In Photochemistry in Organized and Condensed Media, ed. V. Ramamurthy. VCH, pp. 248-302. 

Figure 40. (a) Central picture showing fluoroacetophenone guest triplet G GG spanned by DCA steroid molecules. (t>) Hypothetical arrangement were steroid S, to react with G. (c) Hypothetical arrangement were steroid S2 to react with G. Note the presence of two types of reactive fluoroacetophenone (G and G ) in the DCA complex. In these crystals only G molecules react. Reaction of G molecules with either of the DCA molecules St or S2 will result in short contacts. (Reproduced with permission from M. Vaida, R. Popowitz Biro, L. Leiserowitz and M. Lahav in Photochemistry in Organized and Constrained Media, V. Ramamurthy, Ed., VCH, New York, 1991, p. 247.)... 

Optical rotation, enantiomers, 281 Organic catalysts, 323, 347 crystal morphology, 348 hydrohalogenation, 347 Michael reactions, 350 photochemistry, 348 solid-state reactions, 349 see also specific reactions Organic halides, Grignard reagents, 187, 354 Organocopper chemistry, 199, 208, 292,... 

The central problem in organic solid-state photochemistry is the preorganization of molecules satisfying the topochemical postulates. Schmidt coined the term crystal engineering for this problem of supramolecular assembly. Indeed, the importance of crystal engineering is fundamental to areas as diverse as nonlinear optics, high- /) superconductors, and the generation of polymorph forms in pharmaceuticals. 

Solid-State Organic Photochemistry of Mixed Molecular Crystals... 

Olovsson, G., Scheffer, J. R., and Trotter, J. (1997) Determination of the Absolute Steric Course of an Enantioselective Single Crystal-to-Single Crystal Photorearrangement, J. Am. Chem. Soc., 119, 1462-1463,. (e) Leibovitch, M., Olovsson, G., Scheffer, J. R., and Trotter, J. (1997) Absolute configuration correlation studies in solid state organic photochemistry, PureAppl. Chem., 69, 815-823. 

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