Dihedral angle between two methyl groups of $n$-butane in the gauche and anti forms are

• A

  $60^{\circ}, 0^{\circ}$
• B

  $0^{\circ}, 60^{\circ}$
• Correct answer
  C

  $60^{\circ}, 180^{\circ}$
• D

  $180^{\circ}, 60^{\circ}$

Solution

(The angle between $\mathrm{C}-\mathrm{C}$ and $\mathrm{C}-\mathrm{H}$ bonds on adjacent carbon atoms in any conformation is called dihedral angle.) Hence, the dihedral angle in case of gauche is $60^{\circ}$ and in anti form is $180^{\circ}$.

Hence, the correct answer is option: 'C'.