Question

Which of the following statements regarding $1,3$-dimethyl cyclobutane is correct?

• A. Both cis and trans forms are optically active.
• B. Both cis and trans forms are optically inactive.
• C. The cis form is optically active, while the trans form is optically inactive.
• D. The trans form is optically active, while the cis form is optically inactive.

Answer 1

The correct option is B Both cis and trans forms are optically inactive.

If an identical copy of atoms in one side of the plane is generated with its corresponding side as a mirror image, the molecule is said to have a Plane of Symmetry.

The plane passing through the two diagonally opposite vertices and containing the $C{H}_3$ groups is the plane for $cis$ as well as $trans$ forms.

Conditions for Optical activity:
(i) Absence of plane of symmetry
(ii) Absence of centre of symmetry

Therefore, both cis and trans form are optically inactive.

Hence, (b) is correct.