Alcohols and Phenols are acidic in nature. Electron withdrawing groups in phenol increase its acidic strength and electron releasing groups decrease it. Alcohols undergo nucleophilic substitution with hydrogen halides to yield alkyl halides. Dehydration of alcohols gives alkenes. On oxidation, primary alcohols yield aldehydes with mild oxidising agents and carboxylic acids with strong oxidising agents, while secondary alcohols yield ketones. Tertiary alcohols are resistant to oxidation. The presence of - OH group in phenols activates the aromatic ring towards electrophilic substitution and directs the incoming group to ortho and para positions due to resonance effect.
Answer the following questions :
(i) Why are tertiary alcohols resistant to oxidation ?
Alcohols and Phenols are acidic in nature. Electron withdrawing groups in phenol increase its acidic strength and electron releasing groups decrease it. Alcohols undergo nucleophilic substitution with hydrogen halides to yield alkyl halides. Dehydration of alcohols gives alkenes. On oxidation, primary alcohols yield aldehydes with mild oxidising agents and carboxylic acids with strong oxidising agents, while secondary alcohols yield ketones. Tertiary alcohols are resistant to oxidation. The presence of - OH group in phenols activates the aromatic ring towards electrophilic substitution and directs the incoming group to ortho and para positions due to resonance effect.
Answer the following questions :
(i) Why are tertiary alcohols resistant to oxidation ?
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Solution and Explanation
Oxidation of an alcohol means the carbon that carries the -OH group gains a C=O bond. This carbon is called the carbinol carbon.
To form C=O, the carbinol carbon must lose a hydrogen atom along with the hydrogen of the -OH group.
Step 2: Look at the tertiary alcohol:
A tertiary alcohol has the general formula \(\mathrm{R_3C-OH}\).
Its carbinol carbon is joined to three alkyl groups and the -OH group, so it carries no hydrogen atom.
The C-H bond that is needed for forming C=O is missing.
Step 3: Compare with other alcohols:
A primary alcohol \(\mathrm{RCH_2OH}\) has two such hydrogens and gives an aldehyde, then an acid.
A secondary alcohol \(\mathrm{R_2CHOH}\) has one such hydrogen and gives a ketone.
Under very strong conditions a tertiary alcohol can only break C-C bonds. This gives a mixture of smaller acids and ketones, so we call it resistant.
Final Answer:
The carbinol carbon of a tertiary alcohol has no hydrogen atom, so a carbonyl group cannot form without breaking C-C bonds. \[ \boxed{\text{No H on the carbinol carbon, so no easy oxidation}} \]
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