Name: Preparation of Alcohols
Uploaded: 2019-07-19
Duration: 4 min 43 s
Description: Alcohol is a psychosomatic drug and it is bad for health if consumed. However, it is a useful organic solvent in chemistry labs. Tune in to learn more about...

Question

Describe the mechanism by which the hydroxyl group attached to the aromatic ring is more acidic than the hydroxyl group attached to an alkyl group.

Accepted Answer

The hydroxyl group attached to the aromatic ring is more acidic than the hydroxyl group attached to an alkyl group because phenol is a stronger acid than alcohol. This is due to the presence of hydroxyl group directly attached with ${sp}^{2}$ hybridised carbon of benzene ring which acts as an electron-withdrawing group. This increase in electron density on oxygen and polarity of $O - H$ bond results in an increase in ionization of phenols. When phenols lose a proton it forms phenoxide ion which has negative charge of oxygen atom that delocalised over ortho and para positions of aromatic ring. The greater acidic character of phenols is based on the resonance and stability of phenoxide ion. Any factor which stabilizes the phenoxide ion will increase the acid strength. Whereas, when alcohols lose a proton it forms alkoxide ion that has negative charge localised on oxygen atom and there is no resonance for stabilizing the alkoxide ion in alcohols. Hence, making it less stable and decreasing its acidic strength. Also, the acidic character in phenols increases because of the presence of electron withdrawing group like nitro group. Therefore, phenoxide ion is more stable than alkoxide ion.

Describe the mechanism by which the hydroxyl group attached to the aromatic ring is more acidic than the hydroxyl group attached to an alkyl group.

Important Questions on Alcohols, Phenols and Ethers

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