Optical Isomers

Optical isomerism is a form of stereoisomerism. Stereoisomers have the same structural formula but a different arrangement of atoms in space.A molecule with one chiral centre exists as two optical isomers, called enantiomers. Enantiomers are non-superimposable mirror images of each other.To draw them, show the chiral carbon with two bonds in the plane of the paper, one bond as a solid wedge (coming towards you) and one as a hashed wedge (going away from you). Then draw the second enantiomer as the mirror image of the first. Swapping any two groups on the chiral centre also turns one enantiomer into the other.How do enantiomers differ? They have identical physical properties (melting point, boiling point, density, solubility) and identical chemical reactions with non-chiral reagents. The differences are:
• they rotate the plane of plane-polarised light by the same angle but in opposite directions;
• they can react differently with other chiral molecules.The second point matters in biology and medicine. Enzymes and drug receptors are chiral, so the two enantiomers of a drug can fit a receptor differently: one may be effective while the other is inactive or even harmful.Example: 2-hydroxypropanoic acid (lactic acid), CH₃CH(OH)COOH, has a chiral centre at carbon 2 (bonded to H, OH, CH₃ and COOH), so it exists as two enantiomers.