(a) Give two reactions that show the acidic nature of phenol. [2]
(b) Give chemical reaction for the preparation of phenol from chlorobenzene. [1]
OR
Write IUPAC names of the following compounds - [1+1+1=3]
(a) CH3-CH(Cl)-CH(CH3)-CH(CH3)-CH2OH [pentane chain: C1=CH3, C2 bears Cl

Question

(a) Give two reactions that show the acidic nature of phenol. [2]
(b) Give chemical reaction for the preparation of phenol from chlorobenzene. [1]
OR
Write IUPAC names of the following compounds - [1+1+1=3]
(a) CH3-CH(Cl)-CH(CH3)-CH(CH3)-CH2OH  [pentane chain: C1=CH3, C2 bears Cl, C3 bears CH3, C4 bears CH3, C5=CH2OH; the only -OH is the terminal CH2OH]
(b) CH3-CH(CH3)-O-CH2-CH3  [isopropyl ethyl ether]
(c) [FIGURE: a benzene ring bearing an -OH group at one carbon and a -CH3 group on each of the two carbons ortho to it - 2,6-dimethylphenol]

Accepted Answer

> [!TLDR]
> (a) Phenol behaves as a weak acid: it reacts with NaOH (a base) and with active metals like Na (releasing H2) - genuine tests of the acidic -OH that ordinary alcohols do not give with NaOH. (b) Phenol is made industrially from chlorobenzene only under forcing conditions (NaOH, 623 K, 300 atm - the Dow process). OR: IUPAC naming of the three drawn structures.
>
> (a) Two reactions showing the acidic nature of phenol (its -OH hydrogen is far more acidic than an alcohol's, because the phenoxide ion formed is resonance-stabilised by the aromatic ring):
> 1. Reaction with aqueous sodium hydroxide (a true acid-base reaction - alcohols do NOT react with NaOH, but phenol does): C6H5OH + NaOH -> C6H5ONa (sodium phenoxide) + H2O.
> 2. Reaction with reactive/active metals such as sodium, evolving hydrogen gas: 2C6H5OH + 2Na -> 2C6H5ONa + H2(g).
> The reaction with NaOH is the more diagnostic of the two, because only compounds with a sufficiently acidic -OH (phenols and carboxylic acids) react with a base like NaOH, whereas simple alcohols do not.
>
> (b) Preparation of phenol from chlorobenzene requires drastic conditions because the C-Cl bond in chlorobenzene has partial double-bond character (chlorine's lone pair is donated into the ring by resonance) and resists nucleophilic substitution. Chlorobenzene is heated with aqueous NaOH at about 623 K under about 300 atm pressure (the Dow process) to give sodium phenoxide, which is then acidified to liberate phenol:
> C6H5Cl + 2NaOH --623 K, 300 atm--> C6H5ONa + NaCl + H2O
> C6H5ONa + HCl -> C6H5OH + NaCl.
>
> OR (alternative - IUPAC naming):
> (a) The drawn structure is CH3-CH(Cl)-CH(CH3)-CH(CH3)-CH2OH: a five-carbon chain whose only -OH is the terminal CH2OH, with a -Cl and two -CH3 branches along the chain. The -OH is the principal characteristic group, so it must get the lowest locant; numbering therefore starts from the CH2OH end. C1 = CH2OH, C2 = CH(CH3), C3 = CH(CH3), C4 = CH(Cl), C5 = CH3. This is an alcohol (p

Compound	$pK_a$	Explanation
$\text{CH}_3\text{COOH}$	4.76	Reference (no EWG)
$\text{ClCH}_2\text{COOH}$	2.86	Cl withdraws through one bond
$\text{Cl}_2\text{CHCOOH}$	1.29	Two Cl atoms, stronger withdrawal
$\text{Cl}_3\text{CCOOH}$	0.65	Three Cl atoms, strongest withdrawal
$\text{CH}_3\text{CH}_2\text{COOH}$	4.87	Ethyl group is electron-donating (slightly weaker acid)

Compound	$pK_a$
$\text{ClCH}_2\text{CH}_2\text{COOH}$	4.08
$\text{ClCH}_2\text{CH}_2\text{CH}_2\text{COOH}$	4.52

Compound	pKa	Conjugate base stability
Ethanol	~16	Localized charge on O
Phenol	~10	Delocalized charge via resonance
Acetic acid	~4.76	Even more resonance (two O atoms)

Q.(a) Give two reactions that show the acidic nature of phenol. [2]

Concept understanding — Acidity Of Phenol

Inductive Effect on Acidity – From Intuition to Precision

The Core Intuition

The Precise Statement

Why Distance Matters

Why this formula?

Acidity of Phenol: Why It's More Acidic Than Alcohols

1. The Core Observation

2. The Key: Stability of the Conjugate Base

The Resonance Explanation

3. Why Alcohols Can't Do This

4. The Inductive Effect Also Helps (But Resonance Dominates)

5. The Quantitative Picture (pKa Values)

Q.(a) Give two reactions that show the acidic nature of phenol. [2]

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