Matrix isolation, technique description

This chapter covers photochemical studies of alkenes and cycloalkenes isolated in very low temperature matrices, typically solidified noble gases or nitrogen at temperatures of 10-20 K. Under the conditions of such matrix isolation, trapped species are prevented from diffusing and are therefore prevented from undergoing bimolecular reactions. As a result, extremely reactive species can be stabihzed and investigated by a variety of normal spectroscopic methods, of which IR spectroscopy usually provides the most useful structural information. A brief description of the matrix-isolation technique and an account of its applications in several areas of organic photochemistry are given in a later chapter. 

This chapter provides a brief description of the matrix-isolation technique and then gives some examples of its applications in the study of organic photochemistry. The topics that have been included have been selected from areas of photochemical research to which matrix isolation has made an important and sustained contribution. The choices have been made from among many possibiHties and inevitably reflect the author s personal interests, but, in addition to this more general chapter, two specific areas of matrix photochemistry, alkenes and small ring compounds, are covered in Chapters Y and Z, respectively. 

Particulate interferents can be separated from dissolved analytes by filtration, using a filter whose pore size retains the interferent. This separation technique is important in the analysis of many natural waters, for which the presence of suspended solids may interfere in the analysis. Filtration also can be used to isolate analytes present as solid particulates from dissolved ions in the sample matrix. For example, this is a necessary step in gravimetry, in which the analyte is isolated as a precipitate. A more detailed description of the types of available filters is found in the discussion of precipitation gravimetry and particulate gravimetry in Chapter 8. 

Apart from the number of theoretical studies on n-glucopyranose [257, 258], only one vibrational spectroscopic study of a-D-glucopyranose isolated in Ar matrix has been reported [259]. Laser spectroscopy through UV—UV and IR—UV doubleresonance techniques has contributed to the description of the conformations of some p-phenylglucopyranosides and their hydrates [219, 220, 260, 261] but these studies are limited to vibrational resolution and the structural conclusions are not totally transferable to D-glucose because of the electronic chromophore at the anomeric position. 

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