The best sequence of reactions to prepare 2-heptanone is

Options

A. propyne `overset(NaNH_(2))(to)Xoverset(n-C_(4)H_(9)Br)(to)Yoverset(H_(2)O, Hg^(2+))underset(H_(2)SO_(4))(to)`
B. ethyne `overset(NaNH_(2))(to)Xoverset(n-C_(5)H_(12)Br)(to)Yoverset(H_(2)O, Hg^(2+))underset(H_(2)SO_(4))(to)`
C. 1-hexyne `overset(NaNH_(2))(to)Xoverset(CH_(2)Br)(to)Yoverset(H_(2)O.Hg^(2+))underset(H_(2)SO_(4))(to)`
D. 1-pentyne`overset(NaNH_(2))(to)Xoverset(C_(2)H_(5)Br)(to)Yoverset(H_(2)O, Hg^(2+))underset(H_(2)SO_(4))(to)`

Explanation

To prepare 2-heptanone, we can follow a sequence of reactions starting from ethyne. Here’s a step-by-step breakdown of the process:

### Step 1: Formation of Sodium Ethynide
1. **Starting Material**: Begin with ethyne (HC≡CH).
2. **Reaction with Sodium Amide (NaNH2)**: Treat ethyne with sodium amide (NaNH2) to deprotonate it, forming sodium ethynide (HC≡CNa).
- **Reaction**:
\[ HC≡CH + NaNH2 \rightarrow HC≡CNa + NH3 \]

### Step 2: Nucleophilic Substitution
3. **Nucleophilic Attack**: React sodium ethynide with 1-bromo-3-pentane (C5H12Br), which can be represented as CH3-CH2-CH2-CH2-Br.
- **SN2 Reaction**: The sodium ethynide acts as a nucleophile and attacks the carbon attached to the bromine, leading to the formation of a longer carbon chain.
- **Reaction**:
\[ HC≡CNa + CH3-CH2-CH2-CH2-Br \rightarrow HC≡C-CH2-CH2-CH2-CH3 \]

### Step 3: Hydration of Alkyne
4. **Hydration**: The resulting alkyne (1-heptyne) is then treated with mercuric sulfate (HgSO4) and water (H2O) in the presence of sulfuric acid (H2SO4) to undergo hydration.
- **Markovnikov Addition**: According to Markovnikov's rule, the addition of water occurs such that the hydroxyl (OH) group attaches to the more substituted carbon.
- **Reaction**:
\[ HC≡C-CH2-CH2-CH2-CH3 + H2O \xrightarrow{HgSO4, H2SO4} CH3-CO-CH2-CH2-CH2-CH3 \]

### Step 4: Tautomerization
5. **Tautomerization**: The product undergoes tautomerization to form 2-heptanone.
- **Final Product**:
\[ CH3-CO-CH2-CH2-CH2-CH3 \rightarrow 2-heptanone \]

### Summary of the Reaction Sequence
1. Ethyne → Sodium Ethynide (HC≡CNa)
2. Sodium Ethynide + 1-bromo-3-pentane → 1-heptyne
3. 1-heptyne + HgSO4/H2O → 2-heptanone

### Final Answer
The best sequence of reactions to prepare 2-heptanone is:
1. Ethyne + NaNH2 → Sodium Ethynide
2. Sodium Ethynide + 1-bromo-3-pentane → 1-heptyne
3. 1-heptyne + HgSO4/H2O → 2-heptanone

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