Chemistry - STEREO ISOMERISM Question with Solution | TestHub

Symmetry analysis of (C): The compound is a cyclic dimer of alanine (3,6-dimethylpiperazine-2,5-dione).

Trans form: It contains a Center of Symmetry (COS) at the center of the ring, making it achiral and optically inactive.

Cis form: It lacks both a Plane of Symmetry (POS) and a Center of Symmetry (COS) because the opposite groups across the ring are different ($C=O$ versus $NH$), making it chiral and optically active.

Other options: Options (A), (B), and (D) do not satisfy this condition as their cis forms contain a plane of symmetry and are optically inactive.

Conclusion: Therefore, (C) is the correct option.