22. Rotation around carbon-carbon single bond of ethane is not completely free. Justify the statement.

Alkanes can have infinite number of conformations by rotation around C-C single bonds. This rotation around a C-C single bond is hindered by a small energy barrier of 1-20 kJ mol- due to weak repulsive interaction between the adjacent bonds. Such a type of repulsive interaction is called torsional strain. In staggered form of ethane, the electron cloud of carbon hydrogen bonds are far apart.
Hence, minimum replusive force. In eclipsed electron cloud of carbon-hydrogen become close resulting in increase in electron could repulsion. This repulsion affects stability of a conformer.
In all the conformations of ethane the staggered form has least torsional strain and the eclipsed form has the maximum torsional strain. Hence, rotation around C-C bond in ethane is not completely free.