Question

The structure of naturally occurring steroid cholesterol is given:
Which of the following statements are correct?

This question has multiple correct options.
(A) There are nine chiral centers in the cholesterol
(B) It is a pentacyclic compound
(C) There are two quaternary carbon atoms in the compound
(D) There are six tertiary carbon atoms in the compound

Answer 1

Cholesterol: It is a sterol (or modified steroid), a lipid molecule, and is biosynthesized by all animal cells because it is an essential structural component of all animals (not plant or bacterial) cell membranes that are required to maintain both membrane structural integrity and fluidity.

Complete step by step solution:

A chiral center is defined as an atom in a molecule that is bonded to four different chemical species, allowing for optical isomerism. There are eight chiral centers in cholesterol. There is no internal plane of symmetry so each carbon is different.
Cholesterol contains four rings. So, it is a tetracyclic compound.
Quaternary carbon atom: It is a carbon atom bonded to the other four carbon atoms.
In cholesterol, there are four alicyclic rings and two quaternary carbon atoms in the compound which are ${ C-10 }$ and ${ C-13 }$.
There are six tertiary carbon atoms in the compound which are ${ C-8 }, { C-9 }, { C-14 }, { C-17 }, { C-20 }, and { C-25 }$.

Hence, the correct option is B.

Note: The possibility to make a mistake is that you may choose option C as there are four quaternary carbons but there are four alicyclic rings and two quaternary carbon atoms.