Configurational isomerism changes

This procedure can be employed to advantage in the field of steroids in particular. Configurational isomerization with OH group participation is illustrated in Eq. 151. In this several-step process, the oxirane configuration is not changed. ... 

Transient absorption spectroscopy has been a conventional technique for studying the configurational (conformational) changes that are reflected in the Tn <— T, optical transition. Picosecond to microsecond time-resolved, pump and probe measurement has been widely used to examine the triplet-state isomerizations as far as each ris-T, and the all-trans-Tj species are selectively observed. Even when their wavelengths are very similar to one another, the SVD and global-fitting analysis can successfully identify a set of triplet species appearing in different time-scales, when a correct kinetic model is built. 

CHO, and the double bond between carbons 11 and 12 of the side chain is in the less stable c/s configuration. When rhodopsin absorbs light energy, the less stable 11-c/s double bond is converted to the more stable 11-frans double bond. This isomerization changes the shape of the rhodopsin molecule, which in turn causes the neurons of the optic nerve to fire and produce a visual image. 

A special case of configurational isomerism is represented by the bicyclic host compounds 23 and 24. The synthesis yields both compounds in a 1 1 ratio (total yield 79%) 1. Since 23 and 24 are in/out isomers and can not be interconverted by conformational changes, a pair of ligands with different cavity size is obtained. The difference in size influences their binding abilities both molecules bind naphthalene as well as 2,6- and 2,7-dihydroxynaphthalene in aqueous solution, but only the more spacious out/out isomer 23 is able to complex adamantane and 1-adamantanethiol. To our knowledge this is the first complexation of a pure aliphatic hydrocarbon by any synthetic concave receptor. 

---