Question

The energy barrier to free rotation about carbon carbon bond of ethane is about:

• A. ${30kJmol}^{-1}$
• B. ${3kJmol}^{-1}$
• C. ${3kcalmol}^{-1}$
• D. ${40kJmol}^{-1}$

Answer 1

The correct option is C ${3kcalmol}^{-1}$

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 3 kcal/mol. That is, the eclipsed structure is 3 kcal higher in energy than the staggered structure.