Question

$C_2$ is rotated anti- clockwise ${120}^{\circ }$ about $C_2-C_3$ bond, the resulting conformer is

• A. Partially eclipsed
• B. Eclipsed
• C. Gauche
• D. Staggered

Answer 1

The correct option is C Gauche


Here, after the anti-clockwise rotation of ${120}^{\circ }$ about $C_2-C_3$ axis, the $-C{H}_3$ (bulky) groups on adjacent carbon are at diherdral angle around ${60}^{\circ }$. Thus, the anti-staggered conformer is converted to gauche staggered conformer.