The ultraviolet spectra of hydrazones. Evidence for a steric effect in tetrasubstituted hydrazones

Di- and tri-substituted hydrazones give u.v. spectra having a high-intensity long wavelength band with its position determined by the degree of aryl substitution on the chromophore. In the spectra of tetrasubstituted hydrazones, this long wavelength band is sharply reduced in intensity; this effect is considered to be due to steric hindrance.