Theoretical and Experimental study of dehydroacetic acid, 2- hydroxyacetophenone and 2-acetyl-1,3-cyclohexanodione. UV Visble absorptions, tautomerism and conformational analysis

MARÍA VICTORIA COOKE; GUSTAVO ALEJANDRO ARGÜELLO; DIANA HENAO ARBOLEDA; WALTER JOSE PELÁEZ

Porto

Congreso; Terceiro Simpósio Iberoamericano de Química Orgánica; 2016

As part of our ongoing research on heterocycles and given the structural similarity of dehydroacetic acid (DHAA), 2-hydroxyacetophenone (HAPO) and 2-acetyl-1,3-cyclohexanodione (ACHO) which are compounds widely used in organic synthesis,[1-4] we undertook the present study to better understand their chemical and electronic nature and transitions. This work deals with a comparative study of these three compounds which possess a well-known keto-enol equilibrium in solution. Experimental UV spectra of DHAA, HAPO and ACHO in solvents of different polarity ACN (0.460), EtOH (0.654) and H2O (1.000)[5] were obtained to ascertain the nature of the electronic transitions involved in each molecule. In order to determine the theoretical UV spectra of these compounds, a conformational keto-enol tautomerism analysis of their structures was conducted. With the most stable ones, the UV spectra were calculated in solution at the DFT level of theory using the B3LYP method and 6-31+G(d,p) basis set.It was found that the three compounds are more stable in the enolic conformation than the keto form. Also, HAPO has a very stable enolic structure since the other ones occur with the loss of the aromaticity of the ring. Nevertheless, DHAA and ACHO have two stable enolic structures. The lowest energy transition for DHAA and HAPO is the HOMO-LUMO while for ACHO this transition is forbidden by symmetry.AcknowledgementsThanks are due to CONICET, SECYT and FONCYT for financial support. V.C. thanks CONICET for doctoral fellowship.References(1) Schilf W, Kamieński B, U?arević K. J. Mol. Struct. 2013, 1031, 211-215(2) Rational Approaches to Structure, Activity and Ecotoxycology of Agrochemicals, (Eds: I. Iwataki, W. Draber and T. Fujita), CRC Press, 1992.(3) Conejo M, Ávila P, Álvarez E, Galindo A. Inorg. Chim. Acta. 2016, Article in press.(4) Strakova I, Strakovs A, Petrova M. Chem. Heterocycl. Compd. 2002, 38, 429-433.(5) Solvents and Solvent Effects in Organic Chemistry, (Eds: C. Reichardt), Wiley-VCH, 2003.