Structure and absorption spectra of substituted 2-hydroxy-2-trifluoromethylchroman-4-ones

Abstract

UV absorption spectra of substituted 2-hydroxy-2-trifluoromethylchroman-4-ones (chromanones) in aqueous ethyleneglycol were studied. Replacement of hydrogen in the aromatic ring of the chromanones by CH3 or CF3 groups was shown to cause the molar extinction coefficients of the K, B, and C=O bands to shift from 16,160 to 27,980 and 30,250 dm3/mol·cm; from 12,750 to 17,920 and 16,130 dm3/mol·cm; and from 3850 to 3630 and 2760 dm3/mol·cm, respectively. Increasing the solution pH from 1 to 10.5 affected weakly the aromatic ring bands yet impacted greatly the chromanone carbonyl bands, causing their λmax to shift from 311-326 nm to 342-346 nm and their extinction coefficients to increase from 2760-3850 dm3/mol·cm to 9940-10,160 dm3/mol·cm. A further rise in the pH resulted in hypochromia of the carbonyl band due to the destruction of the chromanones. The results were confirmed by NMR spectroscopy and GC methods. © 2012 Springer Science+Business Media New York.