Optical rotation is the signed angle measured in polarimetry. Positive rotation is clockwise for an observer facing the incoming light; negative rotation is counterclockwise. State the viewing convention, wavelength, temperature, solvent, concentration and path length when comparing measurements. R and S configuration specifies spatial arrangement, and does not predict the sign of optical rotation.[ref]
5.5 Sequence Rules for Specifying Configuration. McMurry, Organic Chemistry, §5.5, discussion after Figure 5.10: no simple relation between R/S and rotation sign
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Optical rotation, also known as optical activity, is the phenomenon where the plane of polarized light is rotated when it passes through certain substances. This effect is observed when light interacts with chiral molecules — that is, molecules that cannot be superimposed on their mirror images, similar to how left and right hands are different.