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Chemistry · Alkanes: Conformations: Sawhorse and Newman projections (of ethane), mechanism of halogenation of alkanes

+\boldsymbol{B} \boldsymbol{r}_{2} \stackrel{\boldsymbol{h} \boldsymbol{v}}{\bol

\( \boldsymbol{C H}_{3}-\stackrel{\boldsymbol{C} \boldsymbol{H}_{3}}{\boldsymbol{C} \boldsymbol{H}}-\boldsymbol{C H}_{3}(\operatorname{excess})+\boldsymbol{B} \boldsymbol{r}_{2} \stackrel{\boldsymbol{h} \boldsymbol{v}}{\boldsymbol{C H}_{3}} \) \( \boldsymbol{C H}_{3}-\underset{\boldsymbol{B} \boldsymbol{r}}{\boldsymbol{C}}-\boldsymbol{C H}_{3}+\boldsymbol{C H}_{3}-\boldsymbol{C} \boldsymbol{H}- \) \( \boldsymbol{C H}_{2}-\boldsymbol{B r} \) The relative reactivity of \( 1^{\circ} H, 2^{\circ} H \) and \( \mathbf{3}^{o} \boldsymbol{H} \) in bromination reaction has been found to be 1: 82: 1600 respectively. In the reaction the percentage yields of the products \( (A) \) and \( (B) \) are expected to be

  • A. 99.4\%, 0.6\%
  • B. 50\%, 50\%
  • C. ०.6\%, 99.4\%
  • D. 80\%, 20\%

Step-by-step solution

Isobutane has 9 primary hydrogens (each with relative reactivity 1) and 1 tertiary hydrogen (reactivity 1600). The product distribution is based on the number of hydrogens times reactivity: primary contribution = 9×1 = 9, tertiary contribution = 1×1600 = 1600, total = 1609. Percentage yields: tertiary bromide (A) = 1600/1609 × 100% ≈ 99.4%, primary bromide (B) = 9/1609 × 100% ≈ 0.6%.
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