Question

Ethyl alcohol and phenol both contain ${\text{OH}}$ group. Why is phenol acidic and alcohol is neutral in nature? Give reason.

Answer 1

Hint: The acidic or basic nature of an organic compound depends upon its conjugate. If the conjugate of a compound is stable after releasing proton then it is acidic in nature and if its conjugate is stable after releasing hydroxide ion then it is basic in nature.

Complete step by step answer:
We can predict about the compound whether it is acidic or not simply by checking the stability of its conjugate compound.
Conjugate is a term which is used to join two things which are exactly the same except any one feature.
Structure of phenol:

Structure of ethyl alcohol:

As we all know that phenol exists in its resonance structure which provides it a further level of stability. During the resonance sometimes the oxygen atom gets a positive charge on it which is the cause of attraction for the electron pairs of the ${\text{OH}}$ group.
Due to this attraction of electron pairs of ${\text{OH}}$ groups the proton is released and an ion named phenoxide ion is formed.
\[{{\text{C}}_6}{{\text{H}}_5}{\text{OH}} \to {{\text{C}}_6}{{\text{H}}_5}{{\text{O}}^ - }{\text{ + }}{{\text{H}}^ + }\]
Due to resonance the phenoxide ion is also stable as the negative charge present on the ring takes part in resonance and stabilizes itself.
While in alcohols as we can predict from their structures, they don’t show resonance which makes it more difficult for them to release a proton. Their conjugate will be unstable if the proton is released, and if forcefully released then the proton will again attach to the conjugate of alcohol.

Note:
Due to the resonance in phenoxide ion the negative charge present on the oxygen atom which is a delocalized charge, gets distributed all over the ring and shared by each and every carbon atom which makes the phenoxide ion stable