1H NMR, 13C NMR and Computational DFT Study of the Structure of 2-Acylcycloalkane-1,3-diones in Solution

1H and13C NMR spectra of 2-acylcyclopentane-1,3-dione [acyl = formyl (1); acetyl (2)] and 2,6-dioxocyclohexanecarboxylic acid (3) have beenmeasured. The optimummolecular 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.