A Solid-State NMR and Theoretical Study of the <sup>17</sup>O Electric Field Gradient and Chemical Shielding Tensors of the Oxonium Ion in <i>p</i>-Toluenesulfonic Acid Monohydrate
Bibliographic record
Abstract
We report a solid-state 17 O NMR study of the 17 O electric field gradient (EFG) and chemical shielding (CS) tensors for the oxonium ion, H 3 O +, in p -toluenesulfonic acid monohydrate (TAM). Both the 17 O EFG and CS tensors of the H 3 O + ion are axially symmetric within the experimental errors. The 17 O quadrupole coupling constant (QCC) is found to be 7.05 ± 0.02 MHz, and the 17 O chemical shift anisotropy (CSA) is 87 ± 5 ppm. Experimental results are compared with extensive quantum chemical calculations using restricted Hartree−Fock approach (RHF), second-order Møller−Plesset perturbation theory (MP2), and density functional theory (DFT). The calculations showed that the strong hydrogen-bonding environment around the H 3 O + ion in TAM is responsible for a reduction of approximately 3 MHz in the 17 O QCC compared to that of an isolated H 3 O + ion. The effective 17 O quadrupole moment is calibrated at the B3LYP/cc-pVTZ level, Q = −2.400 fm 2 . Using this value, we obtained the best calculated 17 O QCC for the “bound” H 3 O + ion, +7.382 MHz, which is in reasonably good agreement with the observed value. The 17 O chemical shielding tensor is also calculated using the GIAO (gauge-including atomic orbital) approach. Although the calculated isotropic 17 O chemical shifts are in excellent agreement with the experimental data, the calculations with all the basis sets employed in the present study invariably underestimated 17 O CSAs by approximately 20 ppm.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
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