Arylazo-steroids. Part V. Optical rotatory dispersion spectra
The o.r.d. spectra of a variety of steroids bearing the arylazo-chromophore at positions 3, 6, 7, and 17 have been recorded and discussed. All showed a Cotton effect associated with the n→π* transition in the visible region; the amplitude of this effect may be correlated with the degree of free rotation of the chromophore and with its distance from the asymmetric centres of the molecule. Attempts have been made to relate the observed signs of the Cotton effect to a sector rule for the arylazo-chromophore. The o.r.d. spectra of arylazo-hydroperoxides were strongly solvent-dependent, owing to the presence of inter- or intra-molecularly hydrogen-bonded forms; by varying the solvent composition isorotatory points were observed. Anomalous substituent effects were shown by a series of ring-substituted derivatives.