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rabindrakr.choudhary , asked a question
Subject: Chemistry , asked on 11/10/11

Phenol is more acidic than alcohol. Give reasons.


prerna.bansal... , Meritnation Expert added an answer, on 12/10/11


Phenol is more reactive and acidic than alcohol (aliphatic) as the phenoxide ion formed in the product is more stable (due to resonance) than alkoxide ion formed in the product side and hence the reaction shifts in forward direction in phenol and is slightly in backward direction in alcohols.

R-OH + NaOH ⇌ R-O-Na + H2O (equilibrium to the left)

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Vipul Kumar , added an answer, on 25/10/11
21 helpful votes in Chemistry

Acidity of any compound is generally directly proportional to its tendency to release H+ ions.

In case of any alcohol ( e.g. CH3-OH ), alkyl group attached to oxygen atom are of electron releasing nature due to+I inductive affect. This character of alkyl groups decreases oxygen's electronegativity and hence its tendency to donate H+ get decreses.

In case of phenol, phenyl group attached to oxygen is of electron withdrawing nature due to -R resonance affect. This character of phenyl group increases the electronegativity of oxygen atom and hence its tendency to donate H+ increases.

Since phenol donate H+ ion easily than alcohols, phenols are more acidic than alcohols.

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Akshita Viswan , added an answer, on 11/10/11
77 helpful votes in Chemistry

  Phenols are more acidic than alcohol since phenols can delocalize its electrons. Also, phenols can remove its hydrogen to make it more stable. The ion is called thephenoxide ion. If you want to see how the electrons delocalize, see this:

For the second question, the acidity of phenols is related to real life. If your family loves you very much, they cannot lose you. However, if your family doesn't love you and they can still survive without you, you might as well go. Phenols and carboxylic acids are like these. Acidity depends on the concentration of H+. Electron releasing groups like alkyl groups makes the phenoxide ion have electrons making the phenol unstable, so it is less acidic. If you have withrawing groups like the most electronegative fluorine, it may make the electrons move into flourine making the phenoxide stable. Hence, making H= come in handy and the mixture more acidic.


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Michalle John , added an answer, on 11/10/11
36 helpful votes in Chemistry

Phenols may be considered to be a resonance hybrid of the five contributing structures. as a result of resonance, the oxygen atom acquires a partial positive charge. this weakens the O-H bond and thus facilitates the release of a proton.

The phenoxide ion thus formed alos exist as a resonance hybrid of five contributing structures. But the phenoxide ion is better stabilised than phenol .However, in case of alcohol, both alcohol molecule and alkoxide ion are represented by one structure each and there is no resonance. The alkoxide ion due to presence of a formal negative charge on it has greater energy and is less stable than alcohol. Thus phenol is more acidic than alcohol

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