Study of hydrogen bonding in 1-ethyl-2-methyl-4-oxo-1,4-dihydro-pyridin-3-yloxyethanoic acid and 3-(1,2-diethyl-4-oxo-1,4-dihydropyridin-3-yloxy)propanoic acid by 1H NMR spectroscopy and X-ray crystallography

A series of 1,2-dialkyl-4-oxo-1,4-dihydropyridin-3-yloxyethanoic acids and 3-(1,2-dialkyl-4-oxo-1,4-dihydropyridin-3-yloxy)propanoic acids have been synthesized via the corresponding pyran-4-ones. Ring proton chemical shifts indicate hydrogen bonding between the side-chain carboxylic acid proton and the 4-oxo group of the heterocycle to be present only for the pyridinone species in DMSO solution. X-Ray crystallography demonstrates the hydrogen bonding in 1 -ethyl-2-methyl-4-oxo-1,4-dihydropyridin-3-yloxyethanoic acid to be very strong (O—O = 2.441 Å) and intramolecular, giving a unique 8-membered chelate ring. The analogous hydrogen bonding in 3-(1,2-diethyl-4-oxo-1,4-dihydropyridin-3-yloxy)propanoic acid is however strong (O—O = 2.541 Å) and inter-molecular, giving an infinite structure.