Question

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

Answer 1

Hint: All the above terms are used in the optical isomerism of organic compounds. Try to figure out what enantiomers are and how they are related to racemates. Interpret the word asymmetric carbon atom grammatically so we can get an idea about it.

Complete answer:
 We know that isomerism is the property of compounds having the same molecular formula but different structural formulas and show the difference in properties. There are two types of isomerism : Structural isomerism and stereoisomerism. In structural isomerism the length of the parent chain may be different, functional groups may be different, the position of the functional group may be different.
Stereoisomerism involves the difference in the position of molecules or functional groups in space. Such as the placement of heavy groups on the same side of the double bond.
(a) Optical activity is the property of optically active compounds to rotate the plane of plane-polarized light. Optically active compounds form nonsuperimposable mirror images. Optically active compounds do not show any symmetry such as symmetry about a point, about a line, and a plane.
 (b) The asymmetric carbon atom is found in organic compounds. A carbon atom attached to four different groups on four different groups through four single bonds is called an asymmetric carbon atom.
(c) Enantiomers are stereoisomers and optically active organic compounds. Enantiomers are mirror images of each other which are non-superimposable.
(d) Racemates are a mixture of two optically active enantiomers. These two enantiomers are mixed in an equal amount so the mixture does not show any optical activity.

Note: Generally compounds containing asymmetric carbon atoms show optical isomerism but in some cases where there are symmetry elements shown by the compound then the compound will be optically inactive. Racemates is also called a racemic mixture that does not rotate the plane of plane-polarized light because both enantiomers rotate light by an equal amount in opposite directions and no overall rotation of light.