Steric and Electronic Effects in Basic Dyes. I—Electronic Absorption Spectra of Derivatives of Malachite Green Containing Trifluoromethyl Groups in the Phenyl Ring

Absorption spectra of derivatives of Malachite Green containing trifluoromethyl groups in the phenyl ring have been examined. As anticipated, substituents in the 3- or 4-position have little effect on the maximum intensity of the first-frequency band but they modify the position of the band to an extent linearly related to the appropriate Hammett substituent constant. Although a substituent in the 2-position markedly increases the intensity of the first band, the expected bathochromic shift relative to that of the 4-substituted isomer is not observed. Steric hindrance of the central carbon atom in the 2-trifluoromethyl and 2,6-di-(trifluoromethyl) derivatives facilitates replacement of a terminal dimethylamino group by a hydroxyl group, with formation of a fuchsone. The hindrance is sufficient to permit replacement of a dimethylamino group in the corresponding dye-bases.