14. If the organic reactant in a Wurtz reaction mixture (RX and sodium) has n C-C
bonds, the hydrocarbon product will have how many C-C bonds?
a. n/2
b. n-1
c. 2n+4
d. 2n+1
The correct answer is d. 2n+1. In the Wurtz reaction, two identical alkyl halide molecules (RX) couple with sodium to form R-R plus sodium halide, adding one new C-C bond to create a symmetric alkane .
Wurtz Reaction Overview
The Wurtz reaction uses dry ether and sodium metal: 2RX + 2Na → R-R + 2NaX. An alkyl halide RX with alkyl group R containing m carbon atoms has n = m-1 C-C bonds, as alkanes follow CmH2m+2 where bonds between carbons total m-1 . The product R-R has 2m carbons, so 2m-1 C-C bonds. Substituting n = m-1 gives 2(n+1)-1 = 2n+1 C-C bonds .
Option Analysis
- a. n/2: Incorrect; halves bonds, but reaction doubles alkyl units and adds one bond (e.g., ethyl halide n=1 yields 3 bonds, not 0.5).
- b. n-1: Incorrect; reduces bonds, opposite of coupling that increases chain length .
- c. 2n+4: Incorrect; overcounts (e.g., methyl n=0 yields 1 bond, not 4) .
- d. 2n+1: Correct; matches mechanism where two R groups (each n bonds) plus one new bond totals 2n+1 (verified: CH3X n=0 → C2H6 with 1; C2H5X n=1 → C4H10 with 3) .
Examples Confirming 2n+1
- Methyl (CH3X): n=0 → ethane (1 C-C bond) = 2(0)+1.
- Ethyl (C2H5X): n=1 → butane (3 C-C bonds) = 2(1)+1 .
- Propyl (C3H7X): n=2 → hexane (5 C-C bonds) = 2(2)+1.
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Wurtz Reaction C-C Bonds: If RX Has n C-C Bonds, Product Has How Many?
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Solve Wurtz reaction MCQ: If organic reactant RX has n C-C bonds, hydrocarbon product has 2n+1 C-C bonds. Detailed mechanism, options explained for CSIR NET, JEE, NEET chemistry prep.
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Why Other Options Fail
| Option | Formula | Example (n=1, ethyl) | Why Wrong |
|---|---|---|---|
| a. n/2 | n/2 | 0.5 | Non-integer; ignores coupling |
| b. n-1 | n-1 | 0 | Reduces bonds, contradicts synthesis |
| c. 2n+4 | 2n+4 | 6 | Excess (butane has 3, not 6) |
| d. 2n+1 | 2n+1 | 3 ✓ | Matches mechanism |
Exam Tips for CSIR NET/JEE/NEET
- Focus on symmetric products from identical RX; mixed halides yield mixtures.
- Reaction suits primary alkyl halides; fails for tertiary due to elimination .
- Practice: odd-carbon alkanes need mixed Wurtz .
- Master for hydrocarbon synthesis questions .
