MCQ
The energy barrier to free rotation about carbon carbon bond of ethane is about :
  • A
    $30 \mathrm{~kJ} \mathrm{~mol}^{-1}$
  • B
    $3 \mathrm{~kJ} \mathrm{~mol}^{-1}$
  • $3 \ \mathrm{kcal}\ \mathrm{mol}^{-1}$
  • D
    $40 \mathrm{~kJ} \mathrm{~mol}^{-1}$

Answer

Correct option: C.
$3 \ \mathrm{kcal}\ \mathrm{mol}^{-1}$
The staggered structure is the structure of lower energy than eclipsed structure.
The relative energy required for complete a rotation in ethane is called the energy barrier to rotation, and it is about $\text{3 kcal/mol.}$
That is, the eclipsed structure is $3 \text{ kcal}$ higher in energy than the staggered structure.

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