Infrarot-Untersuchungen an substituierten Flavanonen und den isomeren 2′-Hydroxychalkonen

Abstract

IR data of eight substituted flavanones and their isomeric hydroxychalkones have been recorded in order to assign the various absorption bands and to study the effect of substituents on C=C out-of-plane deformation (400–700 cm⁻¹), C−H out-of-plane deformation (700–1000 cm⁻¹), C−H in-plane deformation (1000–1300 cm⁻¹), C−O stretch (≈1200 cm⁻¹), OCH₃ (1200–1300 cm⁻¹), O−H deformation (1300–1400 cm⁻¹), CH₃ deformation (1300–1500 cm⁻¹), benzene ring vibration (1400–1600 cm⁻¹) and C=O stretch (≈1650 cm⁻¹). The δ_C−H (ring A) in 2′,4′-dihydroxy-3-nitrochalkone appears at 826 cm⁻¹ (s), while in the isomeric flavanone it shows up as three bands, viz., 807 (w), 833 (m) and 881 cm⁻¹ (w). This difference principally arises due to the presence of the electron withdrawing nitro substituent. The C=O stretching vibration in flavanones appears at a higher frequency than in the corresponding hydroxychalkones. This is perhaps due to the lack of conjugation in the former class of compounds. Chloro substituents (ring B) in different positions exert differing effects on ν_C−O. These differences can be rationalized in terms of a field-effect exerted by the chlorine atom.