Question

Which of the following are chiral and capable of existing as enantiomers?
(i) 1,3-Dibromobutane
(ii) 1,2-Dichlorobutane
(iii) 1,5-Dibromopentane
(iv) 3-Ethylpentane
(v) 2-Chlorobicyclo [1.1.0]butane
(vi) 2- lodobicyclo [3.3.0]octane
(vii)2-Bromobicyclo [2.1.1] hexane
(viii)5-Bromobicyclo [2.1.1]hexane
(A) (a), (b), (f) and (g) only
(B) (a), (b), (e) and (g) only
(C) (a), (b), (d) and (g) only
(D) (a), (b),(c),(e) (f) and (g) only

Answer 1

Hint: Enantiomers are those compounds which have the same formula but have different three dimensional orientation of compounds. These compounds have different chemical properties and the most important point is that there should be an asymmetric carbon present for the formation of enantiomers.

Complete step by step solution:
-Optical isomers are molecules that differ from each other in their behavior towards the plane-polarized light. They have three dimensional arrangements of the same atoms in a molecule.
-In the above given options 1,3-Dibromobutane, 1,2-Dichlorobutane, 2- lodobicyclo [3.3.0]octane and 2-Bromobicyclo [2.1.1] hexane are chiral and are capable of existing as enantiomers.
All these compounds have asymmetric carbon atoms. This asymmetric carbon atom contains four different groups and thus they are chiral. And due to the presence of this chiral center this can exist as an enantiomer.
Let’s explain some of the options:

1,3-Dibromobutane contains an asymmetric carbon at C3 having four different groups attached to it can exist as an enantiomer.

1,2-Dichlorobutane also contains an asymmetric carbon at C-2 position which has 4 different groups attached to it and exists as an enantiomer.

Additional information:
Enantiomers have identical boiling point and melting point because of which they can not be separated using the normal methods of separation like evaporation etc. the enantiomers are non – superimposable mirror images which means that the mirror image of an enantiomer does not impose on each other. Difference between diastereomers and enantiomers is that diastereomers are non- superimposable mirror images and they are easy to separate due to difference in boiling and melting point.

Note: Dextrorotatory and laevorotatory are used to describe the optical rotation of the plane polarized light. Laevorotatory rotates the plane polarized light to the left and the dextrorotatory rotates the plane polarized light to the right depending on the view of the observer.