If an optically active organic substance is labelled in the chirality center with another isotopic species (such as15N for14N) a pronounced variation of rotatory power is predicted. We tried to varify this idea experimentally on L-α-alanine and found
an isotope effect of ORD (optical rotatory dispersion). The magnitude of the rotation is mainly dependent on the pH of the
solvent. The ratio of the optical activity alanine-14N/alanine-15N is about 1.02. The molecular rotations show a consistently lower ratio but it can be seen that the isotope effect is not
only a mass effect.