Hydrocarbons - Result Question 18
1. In the following skew conformation of ethane, $H^{\prime}-C-C-H^{\prime \prime}$ dihedral angle is
(2019 Main, 12 April II)
(a) $58^{\circ}$
(b) $149^{\circ}$
(c) $151^{\circ}$
(d) $120^{\circ}$
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Answer:
Correct Answer: 1. (c)
Solution:
A dihedral angle is the angle between two $C-C$ bonds projected on a plane orthogonal to the $C-C$ bond. In the given skew conformation, having Newman’s projection the dihedral angle is
$$ \begin{alignedat} & H^{\prime}-C-C-H^{\prime \prime} \ &=\left(H^{\prime}-C-C-H _a\right)+\left(H _a-C-C-H^{\prime \prime}\right) \ &=29^{\circ}+120^{\circ}=149^{\circ} \end{aligned} $$
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