Question

On monochlorination of 2-methyl butane, the total number of chiral compounds formed is:
(A) 2
(B) 4
(C) 6
(D) 8

Answer 1

Hint: A carbon atom which has four different atoms or groups attached to it is known as a Chiral carbon. For a chiral carbon in a molecule, there are two optical isomers for it. The number of optical isomers increases exponentially with more chiral carbons in the same fashion.

Complete step by step solution:
-In chemistry, if a molecule cannot be superposed on its mirror image by any combination of rotations and translations, such a molecule or ion is known as chiral.
-A chiral molecule or ion exists in two stereoisomers. Those stereoisomers are non-superimposable mirror images of each other and are known as enantiomers.
-Let us now see how to chiral centres within a molecule.
(i) A chiral molecule usually contains at least one carbon atom with four different substituents attached to it.
(ii) Any molecule which contains a chiral centre is a chiral molecule.
(iii) A chiral molecule will be non-superimposable on its mirror image.
(iv) All straight-chain alkyl group carbons (\[C{{H}_{3}}\] or $C{{H}_{2}}$units) will never be chiral centres as these groups have two or more identical groups that are hydrogens attached to the carbons.
(v) Carbons on double or triple bonds can be chiral centres because they can't have four different groups after double or triple bonds.
(vi) Whenever looking for chiral carbon, look for carbon atoms with substituents for different groups.
-In organic chemistry, the chlorination with a single chlorine atom is known as monochlorination.
-Monochlorination of 2-methyl butane produces products which are given below-

Following the above guidelines, the carbons marked with are identified as chiral centres. Hence there are two chiral molecules.

So, the correct answer is option (A).

Note: Let us now see some important properties of chiral molecules.
-The two enantiomers, which are stereoisomers of chiral molecules or ions, have the same chemical properties except when reacting with other chiral compounds and are distinguished as ‘right-handed’ or ‘left-handed’ by their absolute configuration.
-The two enantiomers have the same physical properties, except that they often have opposite optical activities. Optically active properties mean that when a beam of plane-polarized light passes through a chiral molecule, it interacts with the same molecule in such a way that the angle of the plane of oscillation rotates. A pair of enantiomers always rotates the direction of plane-polarized light to an equal but opposite degree.