An optically active alkyl halide mathrmC_4H_9Br$\mathrm{C_4H_9Br}$ [A] reacts with hot KOH dissolved in ethanol and forms alkene [B] as major product which reacts with bromine to give dibromide [C]. The compound [C] is converted into a gas [D] upon reacting with alcoholic mathrmNaNH_2$\mathrm{NaNH_2}$. During hydration 18 gram of water is added to 1 mole of gas [D] on warming with mercuric sulphate and dilute acid at 333mathrmK$333\mathrm{K}$ to form compound [E]. The IUPAC name of compound [E] is :

### Related Formula Dehydrohalogenation via alcoholic KOH follows E2 elimination mechanism: mathrmR-CH_2-CH(Br)-R' xrightarrowtextalc. KOH R-CH=CH-R'$$\mathrm{R-CH_2-CH(Br)-R' \xrightarrow{\text{alc. KOH}} R-CH=CH-R'}$$ Hydration of alkynes using mathrmHgSO_4/H_2SO_4$\mathrm{HgSO_4/H_2SO_4}$ yields ketones via keto-enol tautomerism. ### Core Logic Let's trace the full sequence line-by-row: 1. **[A]** is an optically active halide with formula mathrmC_4H_9Br rightarrow mathrmCH_3-CH(Br)-CH_2-CH_3$\mathrm{C_4H_9Br} \rightarrow \mathrm{CH_3-CH(Br)-CH_2-CH_3}$ (2-Bromobutane). 2. Reaction of [A] with hot ethanolic KOH produces **[B]** as the major product: mathrmCH_3-CH=CH-CH_3$\mathrm{CH_3-CH=CH-CH_3}$ (But-2-ene). 3. Treatment of [B] with mathrmBr_2$\mathrm{Br_2}$ yields a vicinal dibromide **[C]**: mathrmCH_3-CH(Br)-CH(Br)-CH_3$\mathrm{CH_3-CH(Br)-CH(Br)-CH_3}$ (2,3-Dibromobutane). 4. Reaction of [C] with alcoholic mathrmNaNH_2$\mathrm{NaNH_2}$ converts it via double dehydrohalogenation into gas **[D]**: mathrmCH_3-Cequiv C-CH_3$\mathrm{CH_3-C\equiv C-CH_3}$ (But-2-yne). 5. Hydration of 1 mole of [D] with mathrmH_2O$\mathrm{H_2O}$ in the presence of mathrmHg^2+/H^+$\mathrm{Hg^{2+}/H^+}$ forms an enol intermediate that rapidly tautomerizes to compound **[E]**: mathrmCH_3-CO-CH_2-CH_3$\mathrm{CH_3-CO-CH_2-CH_3}$ (Butan-2-one). ### Step 1: Visualization

### Pattern Recognition Whenever you see a 4-carbon chain undergoing terminal/internal dehydrohalogenation followed by hydration of the resulting alkyne, look closely at the configuration: symmetric or unsymmetric alkyne hydration both systematically lead to Butan-2-one because a stable ketone cannot form on position 1 via standard Kucherov hydration of an internal chain. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 12 Physics: Haloalkanes and Haloarenes Class 11 Chemistry: Hydrocarbons Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids