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Photochemical reactions in crystals occur under conditions of highly restricted molecular mobility such that only one product is generally obtained, even when there are many others that can be observed in the gas phase or in solution. A series of 2-(1-adamantyl)-ortho-alkyl-acetophenones with gamma hydrogen atoms on both the adamantyl and ortho-aromatic groups was selected to determine whether or not one can engineer and observe competing Norrish Type II reaction pathways in the crystalline state. It was shown that excited state competition for hydrogen abstraction between secondary adamantyl and benzylic hydrogens is affected not only by the relative bond dissociation energies but also by the molecular conformation in the crystal. The subsequent fate of the resulting biradical species is determined by competition between radical recombination to form photoproduct and reverse hydrogen atom transfer to regenerate the starting ketone. Crystallographic information, photo-product distributions in solution and in the solid state, and the results of multiple mechanistic experiments including transient absorption spectroscopy in acetonitrile and with nanocrystals suspended in water are reported. The results demonstrate that it is possible to engineer competing reactions in crystals and that consideration of all of the aforementioned factors is necessary in order to account for the observed photoproduct selectivity.
This article was published in the following journal.
Name: The Journal of organic chemistry
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The formation of a solid in a solution as a result of a chemical reaction or the aggregation of soluble substances into complexes large enough to fall out of solution.
Hypertonic sodium chloride solution. A solution having an osmotic pressure greater than that of physiologic salt solution (0.9 g NaCl in 100 ml purified water).
Methods used to measure the relative activity of a specific enzyme or its concentration in solution. Typically an enzyme substrate is added to a buffer solution containing enzyme and the rate of conversion of substrate to product is measured under controlled conditions. Many classical enzymatic assay methods involve the use of synthetic colorimetric substrates and measuring the reaction rates using a spectrophotometer.
Studies designed to examine associations, commonly, hypothesized causal relations. They are usually concerned with identifying or measuring the effects of risk factors or exposures. The common types of analytic study are CASE-CONTROL STUDIES; COHORT STUDIES; and CROSS-SECTIONAL STUDIES.
Works about research studies that evaluate interventions or exposures on biomedical or health-related outcomes. The two main types of clinical studies are interventional studies (clinical trials) and observational studies.