| A combined solid-state 17O NMR and quantum mechanical study of the 17O electric-field-gradient (EFG) and chemical shielding (CS) tensors in selected organic compounds is presented. Analyses of magic-angle spinning (MAS) and stationary 17O NMR spectra of the carbonyl compounds yield the principal components of the 17 O EFG and CS tensors and their relative orientation. This work represents the first comprehensive study of 17O NMR tensors in organic compounds. For the carbonyl compounds examined in this work, the 17 O quadrupole coupling constant (QCC) and the isotropic chemical shifts are found to be in the range of 8.4–10.6 MHz and 300–580 ppm, respectively. The obtained 17O NMR data make it possible to understand the nature of 17O NMR tensors. It is shown that the most paramagnetic component arises mainly from the MO mixings between n and π* orbitals in the carbonyl fragment. It is also shown that the magnitude of the paramagnetic contribution is inversely proportional to the n → π* energy gap. This is an important finding in understanding of the nature of the 17O CS tensor in carbonyl compounds. For the 17O EFG tensors, our investigation showed that the population of the π oxygen 2p orbital is the main factor controlling the magnitude of 17O EFG tensors for carbonyl compounds. We have found that both the 17O CS and EFG tensors are linearly correlated for carbonyl compounds. We demonstrate the utility of solid-state 17O NMR spectroscopy for studying molecular structures, dynamics, and hydrogen bonding interactions. It is anticipated that, in addition to 1H, 13C, and 15N, solid-state 17O NMR will become a new, useful tool in the study of biologically relevant systems. |
