Theoretical and experimental 1H, 13C, 15N, and 17O NMR chemical shifts for 5-halogenouracils

Abstract

Theoretical and experimental 1H, 13C, 15N, and 17O NMR chemical shifts for uracil and 5-halogenouracils were determined and analyzed. The theoretical NMR chemical shifts were calculated based on the HF and MP2 GIAO approach using the 3-21G∗∗, MIDI!, polarized double zeta Hansen–Bouman, and the polarized triple zeta Sadlej basis sets. The solvent effect was checked at the HF/3-21G∗∗ level by surrounding the uracil molecule by seven water molecules. For all the nuclei studied in the series of halogenouracils, linear correlation was tested between the chemical shift (both experimental and theoretical) and halogen electronegativity. All the carbon–proton and one-bond carbon–carbon spin–spin coupling constants were measured and used to assign the carbon signals.