Enantiomers

Optical isomers that are non-superimposable mirror images of each other are called enantiomers (also called enantiomorphs or optical antipodes). 2-Chlorobutane, discussed throughout this section, exists as exactly such a pair of enantiomers (Fig. 10.1). Enantiomers have identical physical properties to each other -- the same melting point, boiling point, density, and refractive index -- except for the sign of their optical rotation: the magnitude of the rotation each produces is equal, but the sign (direction) is opposite, one dextrorotatory and one laevorotatory. Enantiomers likewise have identical chemical properties to each other, except in reactions with another optically active reagent, where the two enantiomers can react at different rates or give different results (because the reagent itself has a fixed handedness). An equimolar mixture of the two enantiomers of a compound -- equal parts dextrorotatory and laevorotatory -- is called a racemic modification or racemic mixture, and is designated with the prefix (dl)- or the symbol (+/-). Such a mixture is optically inactive overall, not because the individual molecules have stopped rotating light, but because the …