Determination of the tautomeric equilibria of pyridoyl benzoyl β-diketones in the liquid and solid state through the use of deuterium isotope effects on (1)H and (13)C NMR chemical shifts and spin coupling constants.
The tautomeric equilibria for 2-pyridoyl-, 3-pyridoyl-, and 4-pyridoyl-benzoyl methane have been investigated using deuterium isotope effects on (1)H and (13)C chemical shifts both in the liquid and the solid state. Equilibria are established both in the liquid and the solid state. In addition, in the solution state the 2-bond and 3-bond J((1)H-(13)C) coupling constants have been used to confirm the equilibrium positions. The isotope effects due to deuteriation at the OH position are shown to be superior to chemical shift in determination of equilibrium positions of these almost symmetrical -pyridoyl-benzoyl methanes. The assignments of the NMR spectra are supported by calculations of the chemical shifts at the DFT level. The equilibrium positions are shown to be different in the liquid and the solid state. In the liquid state the 4-pyridoyl derivative is at the B-form (C-1 is OH), whereas the 2-and 3-pyridoyl derivatives are in the A-form. In the solid state all three compounds are on the B-form. The 4-pyridoyl derivative shows unusual deuterium isotope effects in the solid, which are ascribed to a change of the crystal structure of the deuteriated compound.
Department of Science, Systems and Models, Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark. Electronic address: poulerik@ruc.dk.
Poul Erik
PE
Hansen
Institute of Bio-organic Chemistry, National Academy of Sciences of Belarus, 220141 Minsk, Belarus.
Eugeny V
EV
Borisov
Computational and Systems Medicine, Department of Surgery and Cancer, Imperial College London, Sir Alexander Fleming Building, South Kensington, London SW7 2AZ, UK.
John C
JC
Lindon
D002247:Carbon Isotopes; D066241:Carbon-13 Magnetic Resonance Spectroscopy / Q000379:methods*; D003903:Deuterium; D007659:Ketones / Q000737:chemistry*; D015394:Molecular Structure; D011725:Pyridines / Q000737:chemistry*
D002247:Carbon Isotopes; D007659:Ketones; D011725:Pyridines; D003903:Deuterium
Coupling constants; DFT calculations; Isotope effects on (13)C chemical shifts; Pyridoyl benzoyl β-diketones; Solid state NMR