# Question #9c03f

May 21, 2017

(+) and (-) tell you the direction in which an optically active substance rotates the plane of polarized light.

#### Explanation:

(+) is clockwise rotation (to the right).

(-) is counterclockwise rotation (to the left·

In the above image, the sample has rotated the polarization clockwise by 90°.

If the sample had been pulegone, we would have known it was ($R$)-(+)-pulegone.

If the rotation had been to the left (counterclockwise), the sample might have
been (-)-menthone.