Question

Which of the following molecules are chiral?

(I)

(II)

(III)

(IV)

A.I,III
B.II,III,IV
C.II, IV
D. All of these

Answer 1

We know that a molecule is called chiral that has non-superimposable mirror image. For example, our hands are an example of chiral objects. Generally a molecule is called chiral if it does not have a plane of symmetry.

Complete step by step answer:
Let’s understand the plane of symmetry in detail. A plane of symmetry is an imaginary plane that divides the molecules equally into two halves which are mirror images of each other. We know a molecule is called chiral if it has non-superimposable mirror image. So, if a molecule has a plane of symmetry then the molecule is not chiral. We have to use this principle to identify whether the given molecules are chiral or not.
1 molecule is,

Here, no plane of symmetry present as bisecting the molecule does not result in a superimposable image. And we know if a molecule does not have a plane of symmetry, the molecule is chiral. So, the molecule is chiral.
2 molecule is

If we convert the above Newman Projection to the Fisher projection we get the structure,

We clearly see that the above molecule has a plane of symmetry, so the molecule is achiral.
3 molecule is,

This molecule is chiral as no plane of symmetry present.
Fourth molecule is,

The molecule has a plane of symmetry. So, it is achiral.

Hence, option A is the correct answer.

Note: Always remember that molecules that can exist as enantiomers are called chiral and they are superimposable on their mirror images. Chirality is the sufficient and necessary condition for the existence of isomers. Molecules that are superimposable on their mirror images are said to be achiral.