Chiral environment, chemical behavior

If looked in an isolation, physico-chemical properties (and mathematical) of a chiral molecule and its antipodal counterpart all coincide. However, when chiral structures are considered in an environment, their behavior can be different, such as it occurs, for example, when a chiral molecule interacts with a receptor. Thus, chirality descriptors are useful for modeling properties related to interactions involving chiral centers [Aires-de-Sousa, 2003]. 

Enantiomers, such as the two forms of 2-bromopentane shown in Figure 25.19, have identical physical properties, such as melting and boiling points, and identical chemical properties when they react wifli nonchiral reagents. Only in a chiral environment do they exhibit different behaviors. One of flie more interesting properties of chiral substances is that their solutions may rotate tiie plane of polariz light, as explained in Section 24.4. 

Some of the physical and chemical properties of enantiomers are indistinguishable from one another. For example, both of the optical isomers of 3-methylhexane have identical freezing points, melting points, and densities. However, the properties of enantiomers differ from one another in two important ways (1) in the direction in which they rotate polarized light and (2) in their chemical behavior in a chiral environment. 

Chemical Behavior In a Chiral Environment Optical isomers also exhibit different chemical behavior when they are in a chiral environment (a chiral environment is one that is not superimposable on its mirror image). Enzymes are large biological molecules that catalyze reactions in living organisms and provide chiral environments. Consider the following simplified picture of two enantiomers in a chiral environment ... 

While chirality is a powerful tool for detecting and understanding biochemical weathering processes in the environment, some caveats and precautions should be kept in mind. First, a compound must be asymmetric in order for chirality to be used. Thus, while extrapolations to structurally similar compounds may be plausible [194], such interpretations must be made cautiously in light of the variability in enantiomer behavior of even structurally similar chemicals. An example of such variability is the observation of enantioselective degradation of PCB 136 by rainbow trout, while structurally similar PCB 95 was not degraded [227,232]. 

---