Comprehensive step-by-step solutions to NCERT Exercise 10.19 (Haloalkanes and Haloarenes). Learn how to interconvert functional groups effectively.
(i) Propene to Propan-1-ol
Hydroboration
$$ \text{CH}_3\text{CH}=\text{CH}_2 \xrightarrow[\text{H}_2\text{O}_2/\text{OH}^-]{\text{B}_2\text{H}_6} \text{CH}_3\text{CH}_2\text{CH}_2\text{OH} $$
Strategy: Direct hydration follows Markovnikov's rule (giving propan-2-ol). To get primary alcohol (Anti-Markovnikov product), use Hydroboration-Oxidation .
(ii) Ethanol to But-1-yne
Step-up
$$ \text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{SOCl}_2} \text{CH}_3\text{CH}_2\text{Cl} $$
$$ \text{HC}\equiv\text{CH} \xrightarrow{\text{NaNH}_2} \text{HC}\equiv\text{C}^-\text{Na}^+ $$
$$ \text{CH}_3\text{CH}_2\text{Cl} + \text{NaC}\equiv\text{CH} \to \text{CH}_3\text{CH}_2\text{C}\equiv\text{CH} $$
Strategy: Convert ethanol to halide. React with Sodium Acetylide (from acetylene) to increase carbon chain.
(iii) 1-Bromopropane to 2-Bromopropane
Rearrangement
$$ \text{CH}_3\text{CH}_2\text{CH}_2\text{Br} \xrightarrow{\text{alc. KOH}} \text{CH}_3\text{CH}=\text{CH}_2 \xrightarrow{\text{HBr}} \text{CH}_3\text{CH(Br)}\text{CH}_3 $$
Strategy: Eliminate HBr to form Propene, then add HBr. Addition follows Markovnikov's Rule to put Br on the secondary carbon.
(iv) Toluene to Benzyl alcohol
Side-chain Sub
$$ \text{C}_6\text{H}_5\text{CH}_3 \xrightarrow[\text{h}\nu]{\text{Cl}_2} \text{C}_6\text{H}_5\text{CH}_2\text{Cl} \xrightarrow{\text{aq. KOH}} \text{C}_6\text{H}_5\text{CH}_2\text{OH} $$
Strategy: Free radical chlorination attacks the side chain (benzylic position). Then simple nucleophilic substitution with aqueous KOH.
(v) Benzene to 4-Bromonitrobenzene
EAS
$$ \text{C}_6\text{H}_6 \xrightarrow{\text{Br}_2/\text{FeBr}_3} \text{C}_6\text{H}_5\text{Br} \xrightarrow{\text{HNO}_3/\text{H}_2\text{SO}_4} \text{p-BrC}_6\text{H}_4\text{NO}_2 $$
Strategy: Brominate first. -Br is ortho/para directing. Nitration then yields the para product as major isomer.
(vi) Benzyl alcohol to 2-Phenylethanoic acid
Step-up
$$ \text{PhCH}_2\text{OH} \xrightarrow{\text{SOCl}_2} \text{PhCH}_2\text{Cl} \xrightarrow{\text{KCN}} \text{PhCH}_2\text{CN} \xrightarrow{\text{H}_3\text{O}^+} \text{PhCH}_2\text{COOH} $$
Strategy: Use KCN to add a carbon atom (Step-up reaction), then hydrolyze the nitrile to carboxylic acid.
(vii) Ethanol to Propanenitrile
$$ \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{PCl}_5} \text{C}_2\text{H}_5\text{Cl} \xrightarrow{\text{alc. KCN}} \text{C}_2\text{H}_5\text{CN} $$
Strategy: Convert alcohol to halide, then substitute with Cyanide ion.
(viii) Aniline to Chlorobenzene
Sandmeyer
$$ \text{Ph-NH}_2 \xrightarrow[\text{0-5}^\circ\text{C}]{\text{NaNO}_2 + \text{HCl}} \text{Ph-N}_2^+\text{Cl}^- \xrightarrow{\text{Cu}_2\text{Cl}_2} \text{Ph-Cl} $$
Strategy: Diazotization followed by Sandmeyer's reaction.
(ix) 2-Chlorobutane to 3,4-Dimethylhexane
Wurtz
$$ 2 \text{CH}_3\text{CH(Cl)C}_2\text{H}_5 \xrightarrow[\text{Dry Ether}]{\text{2Na}} \text{CH}_3\text{CH}_2\text{CH(CH}_3)\text{-CH(CH}_3)\text{CH}_2\text{CH}_3 $$
Strategy: Wurtz reaction doubles the carbon chain and mirrors the structure.
(x) 2-Methyl-1-propene to 2-Chloro-2-methylpropane
$$ (\text{CH}_3)_2\text{C}=\text{CH}_2 + \text{HCl} \to (\text{CH}_3)_3\text{C-Cl} $$
Strategy: Simple Markovnikov addition of HCl. The Cl attacks the tertiary carbocation.
(xi) Ethyl chloride to Propanoic acid
$$ \text{C}_2\text{H}_5\text{Cl} \xrightarrow{\text{KCN}} \text{C}_2\text{H}_5\text{CN} \xrightarrow{\text{H}_3\text{O}^+} \text{C}_2\text{H}_5\text{COOH} $$
Strategy: Step-up reaction using KCN, followed by complete hydrolysis.
(xii) But-1-ene to n-Butyliodide
$$ \text{But-1-ene} \xrightarrow{\text{HBr/Peroxide}} \text{1-Bromobutane} \xrightarrow{\text{NaI/Acetone}} \text{1-Iodobutane} $$
Strategy: Anti-Markovnikov addition (Peroxide effect) to get terminal bromide. Then Finkelstein reaction to swap Br for I.
(xiii) 2-Chloropropane to 1-Propanol
Isomerization path
$$ \text{2-Chloropropane} \xrightarrow{\text{alc. KOH}} \text{Propene} \xrightarrow{\text{HBr/Peroxide}} \text{1-Bromopropane} \xrightarrow{\text{aq. KOH}} \text{1-Propanol} $$
Strategy: Eliminate to alkene, then Anti-Markovnikov addition to move functional group to the end.
(xiv) Isopropyl alcohol to Iodoform
$$ (\text{CH}_3)_2\text{CHOH} \xrightarrow{\text{I}_2 + \text{NaOH}} \text{CHI}_3 \downarrow + \text{CH}_3\text{COONa} $$
Strategy: This is the classic Haloform Reaction . Isopropyl alcohol contains the $\text{CH}_3\text{CH(OH)-}$ group required for a positive test.
(xv) Chlorobenzene to p-Nitrophenol
$$ \text{Ph-Cl} \xrightarrow{\text{HNO}_3/\text{H}_2\text{SO}_4} \text{p-Cl-C}_6\text{H}_4\text{NO}_2 \xrightarrow[\text{443K, H}^+]{\text{NaOH}} \text{p-HO-C}_6\text{H}_4\text{NO}_2 $$
Strategy: Nitration first (ortho/para). The presence of $-\text{NO}_2$ at para position activates the ring for Nucleophilic substitution of Cl by OH.
(xvi) 2-Bromopropane to 1-Bromopropane
$$ \text{CH}_3\text{CH(Br)CH}_3 \xrightarrow{\text{alc. KOH}} \text{Propene} \xrightarrow{\text{HBr/Peroxide}} \text{CH}_3\text{CH}_2\text{CH}_2\text{Br} $$
Strategy: Elimination followed by Anti-Markovnikov addition.
(xvii) Chloroethane to Butane
$$ 2 \text{C}_2\text{H}_5\text{Cl} + 2\text{Na} \xrightarrow{\text{Dry Ether}} \text{C}_4\text{H}_{10} $$
Strategy: Classic Wurtz Reaction to double the carbon chain.
(xviii) Benzene to Diphenyl
Fittig
$$ \text{C}_6\text{H}_6 \xrightarrow{\text{Cl}_2/\text{FeCl}_3} \text{C}_6\text{H}_5\text{Cl} $$
$$ 2 \text{C}_6\text{H}_5\text{Cl} + 2\text{Na} \xrightarrow{\text{Dry Ether}} \text{Ph-Ph} $$
Strategy: Convert benzene to chlorobenzene. Then use Fittig Reaction to couple two aryl rings.
(xix) tert-Butyl bromide to Isobutyl bromide
$$ (\text{CH}_3)_3\text{CBr} \xrightarrow{\text{alc. KOH}} (\text{CH}_3)_2\text{C}=\text{CH}_2 $$
$$ (\text{CH}_3)_2\text{C}=\text{CH}_2 \xrightarrow{\text{HBr/Peroxide}} (\text{CH}_3)_2\text{CH-CH}_2\text{Br} $$
Strategy: Dehydrohalogenation gives isobutylene. Peroxide effect adds HBr to the less substituted carbon (primary bromide).
(xx) Aniline to Phenylisocyanide
Carbylamine
$$ \text{Ph-NH}_2 + \text{CHCl}_3 + 3\text{KOH(alc)} \xrightarrow{\Delta} \text{Ph-NC} + 3\text{KCl} + 3\text{H}_2\text{O} $$
Strategy: This is the Carbylamine Reaction , a test for primary amines resulting in a foul-smelling isocyanide.
Key Reaction Mechanisms Used
Markovnikov's Rule
Anti-Markovnikov (Peroxide)
Wurtz & Fittig
Sandmeyer
Nucleophilic Substitution
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