Probing Hyperconjugation Experimentally with the Conformational Deuterium Isotope Effect
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Bibliographic record
Abstract
Hyperconjugation underlies many chemical phenomena of fundamental and practical importance. Owing to a great deal of interest in the anomeric effect, anomeric-like hyperconjugative effects have been thoroughly investigated in oxygen-containing systems. However, such interactions in the second- and third-row chalcogens are less well-understood and have generated some controversy. Here, we show that the conformational deuterium isotope effect, in combination with Saunders' isotopic perturbation method, permits sensitive and direct experimental probing of the conformational equilibria in dioxane, dithiane, and diselenane analogues by variable-temperature, dynamic NMR spectroscopy. We find that the magnitude of the conformational deuterium isotope effect is 252.1, 28.3, and 7.1 J/mol (±10%) for the oxygen, sulfur, and selenium analogues, respectively. These results reveal the periodic trend for hyperconjugation in the chalcogens, which reflect a decreasing n(x)→σ(C-H(D)) interaction throughout the period, as supported by IR spectroscopy and in agreement with DFT calculations and a natural bond order analysis.
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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 | 0.001 | 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) | 0.002 | 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 it