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A revised absolute magnetic shielding scale for oxygen is established based on a recently reported highly precise experimental measurement of the [SUP17]O spin-rotation constant in carbon monoxide. The isotropic oxygen magnetic shielding constant for [SUP12]C[SUP17]O at the equilibrium geometry, σ[SUBe], is found to be -56.8 ± 0.6 ppm. The experimental rovibrationally averaged value of the shielding constant at 300 K, 〈&sigma 〉[SUB300K], is -62.7 ±0.6 ppm, in excellent agreement with the ab initio value reported by Vaara et al. [J. Chem. Phys. 109, 8388 (1998)]. Based on the revised scale and on experimentally known oxygen chemical shifts, 〈σ〉[SUB300K] (H[SUB2]O(l)) is 287.5 ± 0.6 ppm and 〈σ〉 [SUB300K] (H[SUB2]0(g)) is 323.6 ± 0.6ppm. [ABSTRACT FROM AUTHOR]

Among the interactions which govern NMR spectra, spin-spin coupling interactions provide the most direct form of structural information which is of interest to chemists. Dipolar coupling may be used to measure internuclear distances directly and J coupling may be used to identify bonding interactions and provide insights into the nature of the bonds. It is well known that the presence of a quadrupolar interaction reintroduces the dipolar interaction in spinning samples; however, similarly to the J coupling, this information is often lost if the observed nucleus is quadrupolar due to quadrupolar spectral broadening. Here we show for multiple spin pairs that double-rotation (DOR) NMR fully removes the effects of the quadrupolar interaction on the NMR spectrum leaving only the effects of dipolar and J couplings. We also demonstrate that the J coupling multiplets do not disappear for quadrupolar A2 spin pairs as they do for spin-1/2 nuclei. With DOR NMR, it is then straightforward to measure homonuclear J coupling constants between magnetically equivalent quadrupolar nuclei. A deeper understanding of the origins of the magnitudes and dominant mechanisms of J coupling for quadrupolar spin pairs in a series of related compounds is obtained by decomposing computed J coupling constants into their major molecular orbital contributions. [ABSTRACT FROM AUTHOR]