9 - Stereochemistry of Carbon Compounds

Abstract

Publisher Summary Stereochemistry deals with the influence of molecular configuration and conformation on the physical and chemical properties of molecules. Cis- and trans-isomers differ in physical, chemical, and occasionally physiological properties. An isomer of unknown geometry may be converted into a compound of established configuration if a suitable reference compound is available. Nevertheless, the assignment of configuration to the pairs can be a difficult problem. Dipole moment measurement gives a clear-cut decision in cases where similar polar groups are attached to the double bond; for example, all the trans-dihalogenoethylenes have zero dipole moment. Interconversion of cis- and trans-isomers, a process that has come to be known as stereomutation, occurs with varying degrees of facility by the agency of heat, light, or catalysts. The conformations of a molecule are the different arrangements of the constituent atoms in space, obtained by the rotation or twisting of single bonds. Stereochemical techniques and applications involve the use of polarimetric measurements, optical resolution, racemization, and Walden inversion. Even in cases where chemical transformations involve the asymmetric carbon atom, absolute configurations can be assigned if the mechanism of the reaction is known, with certainty and the processes involved are kinetically controlled.