Question

Which cycloalkane is almost considered to be a planar molecule?
(A) Cyclohexane
(B) Cyclopropane
(C) Cyclopentane
(D) None of the above

Answer 1

In chemistry, planar molecules are referred to as the molecules in which all of their atoms lie in the same plane. In planar molecules, all the atoms are arranged in such a manner that all the atoms are only in a single plane. So, we will study the structure of the cycloalkanes given in the option and predict whether their atoms lie in the same plane or not.

Complete step by step answer
First, we will understand the basic structure of cycloalkanes. As they are alkanes means there is no unsaturation the compound is saturated. All the bonds in cycloalkanes are single. All the cycloalkanes are monocyclic saturated hydrocarbons which consist of carbon and hydrogen only. They are monocyclic means there will be only one cycle. Now we will study the structure of the given compounds one by one.
-The first is cyclohexane. It is not a planar molecule because all the six carbon atoms are not in the same plane. Therefore, this option will not be correct.
-The second is cyclopropane. This molecule is necessarily planar. As in the molecule cyclopropane, all the three carbon atoms at the corner form an equilateral triangle. Therefore, they will be on the same plane.
Now the last molecule cyclopentane. This is not a Planar but almost considered to be a planar molecule. Due to its atoms, it takes the shape of;’ envelope’
Therefore, the correct option is (C).

Note:
Cyclohexane is considered the most stable cycloalkane due to its perfect geometry. All the hydrogen atoms in cycloalkane are eclipsed and the angle is the ideal tetrahedral angle. There is no ring strain like cyclopentane.