A feature of some optical rotatory dispersion spectra that is usefully correlated with conformational and structural features of a molecule. A sharp peak in optical rotation followed by a deep trough is seen as the wavelength decreases; the wavelength between the peak and the trough where the rotation is zero is the point of maximal absorbance. A negative Cotton effect is the reverse, i.e. a fall in rotation followed by a steep rise as the wavelength decreases.