Question

How many chiral centres are there in cholesterol?

Answer 1

Hint : In order to answer the question, first we will discuss the brief explanation of the meaning of chiral centres which are present in cholesterol and then we will mention all types of chiral centres present in cholesterol.

Complete Step By Step Answer:
There are eight chiral centres in cholesterol.
Remember that bond-line structures don't show the hydrogen atoms that are attached to carbon. There is no internal plane of symmetry, so every carbon atom is different. Each chiral carbon must have four different groups. I have circled the chiral centres in the molecule.
The eight chiral centres (with the attached groups) are:
(i) $ {C_3}\left( {OH,{C_4},{C_2},H} \right) $
(ii) $ {C_8}\left( {{C_9},{C_{14}},{C_7},H} \right) $
(iii) $ {C_9}\left( {{C_{10}},{C_8},{C_{11}},H} \right) $
(iv) $ {C_{10}}\left( {{C_5},{C_9},{C_1},{C_{19}}} \right) $
(v) $ {C_{13}}\left( {{C_{14}},{C_{17}},{C_{12}},{C_{18}}} \right) $
(vi) $ {C_{14}}\left( {{C_{13}},{C_8},{C_{15}},H} \right) $
(vii) $ {C_{17}}\left( {{C_{13}},{C_{20}},{C_{16}},H} \right) $
(viii) $ {C_{20}}\left( {{C_{17}},{C_{22}},{C_{21}},H} \right) $
A chiral center is defined as an atom in a molecule that is bonded to four different chemical species, allowing for optical isomerism. It is a stereo center that holds a set of atoms (ligands) in space such that the structure may not be superimposed on its mirror image.

Note :
Chiral molecules usually contain at least one carbon atom with four nonidentical substituents. Such a carbon atom is called a chiral center (or sometimes a stereogenic center), using organic-speak.