Solid-state 17 O NMR study of 2-acylbenzoic acids and warfarin.

We report synthesis and solid-state 17 O NMR characterization of four site-specifically 17 O-labeled 2-acylbenzoic acids (2-RC(O)C6 H4 COOH) where R=H and CH3 ): 2-[3-17 O]formylbenzoic acid, 2-[1,2-17 O2 ]formylbenzoic acid, 2-[3-17 O]acetylbenzoic acid, and 2-[1,2,3-17 O3 ]acetylbenzoic acid. In the solid state, both 2-formyl- and 2-acetyl-benzoic acids exist as the cyclic phthalide form each containing a five-membered lactone ring and a cyclic hemiacetal/hemiketal group. Static and magic-angle-spinning 17 O NMR spectra were recorded at 14.1 and 21.1T for these compounds, from which the 17 O chemical shift and nuclear quadrupolar coupling tensors were determined for each oxygen site. These results represent the first time that 17 O NMR tensors are fully characterized for lactone, cyclic hemiacetal, and cyclic hemiketal functional groups. We also report solid-state 17 O NMR data for the cyclic hemiketal group an anticoagulant drug, warfarin. Experimental 17 O NMR tensors in these compounds were compared with computational results obtained with a periodic DFT code BAND.