The anti-conformation of `n`-butane is more stable than its gauche conformation by about

Options

A. `5KJ mol^(-1)`
B. `3.8KJ mol^(-1)`
C. `6.2KJ mol^(-1)`
D. `4.5KJ mol^(-1)`

Answer

B

Explanation

The anti conforamtion is more stalbe by about `3.8KJmil^(-1)` than the gauche. Both are free of torsional strain. But in a gauche conformation, the two methyl groups are crowded together, i.e., are thrown together closer than the sum of their van der Waals radii. Under these conditions, van der Waals forces are repulsive and raise the energy of the conformation.