Why phenol or benzenol is acidic and Why carboxylic acid is more acidic than phenol ?

Why phenol or benzenol is acidic ?

Oxygen is more electronegative than hydrogen element . So, O – H bond of phenol is polar . Besides this, the lone pair on oxygen atom participate in resonance with the pi electron of benzene ring .

As a result, the oxygen atom of phenol gets partially positive charge . Hence it attracts the O – H bonded electron towards itself .

Therefore , O – H  bond becomes more weak and easily break to release H⁺ ion .

Consequently , phenol or benzenol is acidic in nature .

How would you prove that phenol is acidic ?

There are few chemical reaction which can prove the acidic nature of phenol .  

For example , reaction of phenol  with metallic sodium produced  hydrogen .

 This reaction indicate that phenol is acidic .  In addition to , reaction of  phenol with strong base sodium hydroxide  gives phenoxide salt and water which prove the acidic nature of phenol.

Why carboxylic acid is more acidic than phenol ?

Both carboxylic acid and phenol are ionized in aqueous solution and give carboxylate  and phenoxide anion respectively . Now , the strength of acid depends on relative stability of their concerned anion .

Carboxylate anion have two equivalent resonating structure . The negative charge on oxygen atom equally spread out between two oxygen atom.

On the other hand,in case of phenoxide anion , there are five resonating structure. But the negative charge carry the less electronegative carbon atom .

Consequently, the relative stability of carboxylate anion is higher than phenoxide anion. Therefore , carboxylic acid is more acidic than phenol .

Why is carboxylic acid more acidic than alcohol ?

If carboxylic acid is ionized in aqueous solution ,it gives H⁺ cation and carboxylate anion . On the other hand , on ionization , alcohol gives H⁺ cation and alkoxide anion .

Now, the strength of acid depends on the relative stability of their concerned anion ( that is conjugate base ) . 

Carboxylate anion have two equivalent resonating  structure through which it is stabilized . 

But alkoxide anion have no such type of resonating structure . In addition to, +I effect of alkyl group destabilized the alkoxide anion .

Consequently, carboxylic acid more acidic than alcohol .

Summary:

Why phenol or benzenol is acidic ?

Why carboxylic acid is more acidic than phenol ?

Why is carboxylic acid more acidic than alcohol ?

Why boiling point of alcohol is higher than ether ? Click here.

Why is pyridine more basic than pyrrole and Why phenols are more acidic than methanol ?

Why is pyridine more basic than pyrrole ?

The strength of basicity depends on the tendency to donate an electron to the electron deficient element, ion or group. 

In case of pyrrole, the lone of electrons on nitrogen atom takes part in the resonance with the pi electron of pyrrole ring, through which pyrrole attain the Huckel’s rule of aromaticity.

Why C – O bond length in phenol is less than methanol and what is Bouveault Blanc reduction ?

Why C – O bond length in phenol is less than methanol ?

In case of phenol, the lone pair on oxygen atom takes part in resonance with the π – electron of benzene ring . As a result, the C – O bond gets double bond character . So the C – O bond length decreases.

On the other hand , no such type resonance is happened in methanol.

Why is chlorine, ortho and para directing and Why ‘Cl’-atom can not form H-bond but ‘N’-atom can ?

Why is chlorine, ortho and  para directing  in spite of deactivating group ?

Most of the reaction of chloro benzene [such as nitration, sulphonation, halogenations  and Friedel craft reaction etc ] are electrophilic reaction. Now, –Cl group is a deactivating group.

Due to – I effect, chlorine atom attract electron from benzene nucleus towards itself .

But, due to + R effect ,the lone pair of ‘Cl’-atom participate in resonance with the π electron of benzene nucleus.

Why the nucleophilic substitution reaction of 1-chloro-2,4,6-trinitro benzene occurs very easily ?

Why the nucleophilic substitution reaction of 1-chloro-2,4,6-trinitro benzene occurs very easily?

1-chloro-2,4,6-trinitro benzene contains three nitro groups which are strong electron with drawing group. 

Due to –R effect of this three nitro group , the density of electron of benzene nucleus very much decrease . 

Therefore, the benzene nucleus becomes very much active for nucleophilic substitution reaction. 

Hence, a very weak  nucleophile even water molecule as a nucleophile can attack the targeted carbon atom .