Photolysis, tautomerism and conformational analysis of dehydroacetic acid and a comparison with 2-hydroxyacetophenone and 2-acetyl-1,3-cyclohexanodione

Abstract

The purpose of this work was to determine the tautomerism, the conformational analysis and photoreactivity of dehydroacetic acid (DHAA, 1 ). For that reason, the photolysis of DHAA ( 1 ) was performed at 254 nm and compared with two structurally similar compounds: 2-hydroxyacetophenone (HAP, 2 ) and 2-acetyl-1,3-cyclohexanodione (ACH, 3 ). We confirmed the degradation of 1 to acetic acid and we propose a mechanism on the assumption that a [2+2] cyclodimerization occurs (after UV light absorption) followed by some consecutive Norrish Type I cleavages, affording ketenes that end-up in acetic acid. The UV absorption study was conducted for all three compounds to gain insight about their electronic transitions, both experimentally and with computational simulations using TDDFT (B3LYP/6-31+G(d,p)) methods. A detailed analysis of the different tautomers and isomers that can be present in solution and the MOs involved in the electronic transitions was also achieved. The HOMO→LUMO transition was the least energetic optically active transition for 1 and 2 , whereas 3 was recognized to have a HOMO-1→LUMO transition. These transitions were all of n→π ∗ character.

Complexation of Flavonoids: Spectral Phenomena, Regioselectivity, Interplay with Charge and Proton Transfer

“…Thus, flavanones have not only phenolic chromophore localized on the side benzene ring but also “ o ‐oxy benzaldehyde” one (BA) (Figure 2b). In the result, all the flavanones have absorption spectra similar to those of o ‐R‐oxy acetophenones and o ‐R‐oxy benzaldehydes: they contain a long‐wavelength absorption band of low intensity centered at 320–340 nm and a short‐wavelength intense band at 270–290 nm [14,16,17] . The addition of hydroxyl groups to the benzene ring of chromanone fragment leads to similar shifts of absorption bands of flavanones and corresponding acetophenones [15] …”

“…320-340 nm and a short-wavelength intense band at 270-290 nm. [14,16,17] The addition of hydroxyl groups to the benzene ring of chromanone fragment leads to similar shifts of absorption bands of flavanones and corresponding acetophenones. [15] The fluorescent properties of flavanones are also similar to those of corresponding o-hydroxy benzaldehydes and ohydroxy acetophenones.…”