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 distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".