1H NMR, 13C NMR and computational DFT study of the structure of 2 -acylcycloalkane -1,3 -diones in solution

1 H and 13 CNMR spectra of 2-acylcyclopentane-1,3-dione [acyl = formyl (1); acetyl (2)] and 2,6-dioxocyclohexanecarboxylic acid (3) have been measured. The optimum molecular structures of endo- and exo-enolic forms of investigated objects in solution have been found using DFT method with B3LYP functional and 6-311G(2d,p) basis set. The theoretical values of the NMR parameters have been then calculated using GIAO-DFT method with the same functional and basis set. The theoretical data obtained for compounds 1-3 have been used to interpret their experimental NMR spectra in terms of the equilibrium between different tautomers. It has been found that for investigated triketones an endo-tautomer overwhelmingly prevails.