Question

Define (a) Optical activity
(b) Asymmetric carbon atom
(c) Enantiomers
(d) Racemates.

Answer 1

(a) Optical activity is the ability of chiral molecule to ratate plane plarized light.

(b) Asymmetric carbon atom: A tetrahedral carbon atom which is bonded to four different atoms or groups is called an asymmetric or chiral carbon atom. It is denoted by an asterisk $(\ast )$ on it as shown below. Here, carbon atom is attached to four different groups.
(c) Enantiomers: Stereoisomers which are non-superimposable mirror images of each other and rotate the plane polarized light through the same angle but in opposite directions are known as enantiomers. Enantiomers have identical physical properties like melting point, boiling point, density, refractive index, etc. The two enantiomers of Lactic acid which are non-super impossible mirror images of each other are given below.
(d) Racemates: A mixture containing two enantiomers in equal proportions will have zero optical rotation, as the rotation due to one isomer will be cancelled by the rotation due to the other isomer. Such a mixture is known as racemic mixture or racemate. A racemic mixture is represented by prefixing dl or $(\pm )$ before the name, for e.g., $(\pm )$ butan-$2$-ol.