# Optical activity - 3 | Stereoisomers

Molecule A has an [$\mathrm{\alpha }$]D = - 88°.

Draw the structure of B, which has an [$\mathrm{\alpha }$]D = + 88°.

Calculate the [$\mathrm{\alpha }$]D of a 70/30 mixture of A and B.

Draw the structure of C, which is a constitutional isomer of A and has an [$\mathrm{\alpha }$]D = 0°.

Other answers are also possible for C.

[$\mathrm{\alpha }$]D of a 70/30 mixture of A and B: (-88) x (0.7) + (+88) x (0.3) = -35.2°.