Q.What is optical isomerism? Give one example for each of d & l configuration of same enantiomer. (1+2)

Optical isomerism occurs in molecules with a chiral centre; the two mirror-image forms are called enantiomers, labelled d (dextrorotatory) and l (levorotatory) by the direction they rotate plane-polarised light.

What is optical isomerism:

A compound shows optical isomerism when it contains a chiral (asymmetric) carbon atom — one bonded to four different groups. Such a molecule is non-superimposable on its own mirror image, and the two mirror-image forms are called enantiomers. Enantiomers have identical physical and chemical properties in an achiral environment but differ in how they rotate the plane of plane-polarised light: one rotates it clockwise (dextrorotatory, denoted d or +), the other rotates it anticlockwise by an equal angle (levorotatory, denoted l or -).

Example — 2-chlorobutane:

CH3-*CHCl-CH2-CH3 has one chiral carbon (C2, bonded to Cl, H, CH3, and C2H5 — four different groups).

• d-2-chlorobutane: the (+)-rotating enantiomer …