Question

In $C{H_3}C{H_2}OH$, the bond that undergoes heterolytic cleavage most readily is:
A.$C - C$
B.$C - H$
C.$C - O$
D.$O - H$

Answer 1

Hint:We can define bond cleavage (or) bond fission as the splitting of chemical bonds. This could be referred to as dissociation when a molecule is cleaved to two or more fragments. We can classify bond cleavages into two types depending on the process:
-Homolytic cleavage
-Heterolytic cleavage

Complete step by step answer:

We can say in heterolytic cleavage or heterolysis, the bond breaks in pattern, which the originally-shared pair of electrons remain with one of the fragments. Thus, a fragment gains an electron, containing both bonding electrons, whereas the other fragment loses an electron. This process is called ionic fission.
Heterolysis takes place in reactions, which involve electron donor ligands and transition metals that have empty orbitals.
Heterolytic fission takes place when the two atoms have differences in their electronegativities. The higher the difference in electronegativities of the bonded atoms more would be the trend of heterolytic cleavage of the bond.
In ethanol, $C{H_3} - C{H_2} - OH$
We can write the order of electronegativity as,
$H < C < O$
The electronegativity of hydrogen is $2.2$.
The electronegativity of carbon is $2.55$.
The electronegativity of oxygen is $3.44$.
We shall calculate the electronegativity differences in the given bonds:
In $C - C$, the electronegativity difference is zero. Therefore, the bond does not undergo heterolytic cleavage. Therefore, Option (A) is incorrect.
In $C - H$, the electronegativity difference is $0.35\left( {2.55 - 2.2} \right)$. Therefore, the bond does not undergo heterolytic cleavage since there is not much difference in electronegativity values. Therefore, Option (B) is incorrect.
In $C - O$, the electronegativity difference is $0.89\left( {3.44 - 2.55} \right)$. Therefore, the bond does not undergo heterolytic cleavage since there is not much difference in electronegativity values. Therefore, Option (C) is incorrect.
In $O - H$, the electronegativity difference is $1.24\left( {3.44 - 2.2} \right)$. Therefore, the bond undergoes heterolytic cleavage since there is much difference in electronegativity values. Therefore, Option (D) is correct.
\[O - H\] bond undergoes cleavage most readily since there is large electronegativity between oxygen and hydrogen. Further, oxygen is highly electronegative and could accommodate the negative charge more efficiently developed after the cleavage.
$C{H_3}C{H_2}O - H + Na \to C{H_3}C{H_2}\mathop O\limits^ - N{a^ + } + \dfrac{1}{2}{H_2}$


Note:
We must remember that in biochemistry, catabolism is the method of breaking down large molecules by splitting their inside bonds. Enzymes that catalyze cleavage of bonds are called as lyases. The energy that is needed to break the bond is known as heterolytic bond dissociation energy that is not equivalent to homolytic bond dissociation energy usually used to denote the energy value of a bond.