Experimental Evidence for Negative Hyperconjugation as a Component of the Polar Effect: Variation of the Ease of α-Sulfonyl Carbanion Formation with the Orientation of a β-Alkoxy Substituent
Bibliographic record
Abstract
We report evidence for a strongly geometry-dependent substituent effect. The rate constants for H−D exchange of the α-hydrogens, ( k exch ) OR, in a set of 19 β-alkoxy sulfones of known, fixed (or strongly preferred) H−C α −C β −OR torsion angles have been measured. Those of corresponding model compounds lacking the alkoxy group, ( k exch ) model, were also measured, thereby providing the ratio, k N = ( k exch ) OR /( k exch ) model; the k N values so obtained range over more than 4 orders of magnitude. We show that when due allowance is made for steric and other influences, our observations are consistent with an equation of the form log k N = a + b cos 2 θ (where a = 1.70 ± 0.17 and b = 2.62 ± 0.20) . It is further shown that the observed rate constant ratios are not consistent with a substituent effect consisting only of the inductive effect and the field effect, and that they are fully consonant with the additional presence of a third effect, namely negative hyperconjugation or the generalized anomeric effect, specifically a torsion-angle-dependent donation of the partial negative charge of the incipient carbanion into the orbital. This effect is largest with torsion angles of 0 and 180° and at these torsion angles constitutes the major source of stabilization of the incipient carbanion by the β-alkoxy group. The present observation of a torsion-angle-dependent substituent effect may be combined with the known adherence of the specific rate of α-sulfonyl carbanion formation to the Taft equation, to provide an equation yielding torsion-angle-dependent Taft σ* constants for the alkoxy group: ( ) OR = 0.35 + 0.55 cos 2 θ. The idea of torsion angle dependence is usefully applied to the long-standing problem of the mechanisms of base-promoted elimination with 2-tosyloxycyclohexyl p -tolyl sulfones.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| 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 | 0.000 |
| 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".