Using Incoming Nucleophile Primary Hydrogen−Deuterium Kinetic Isotope Effects To Model the S<sub>N</sub>2 Transition State
Bibliographic record
Abstract
The primary hydrogen−deuterium incoming nucleophile KIEs for the S N 2 reactions between para-substituted benzyl chlorides and borohydride ion in DMSO at 30.000 ± 0.002 °C are small (≤1.14) and insensitive to a change in substituent at the α-carbon. The small Hammett ρ (0.51) and ρ r (−0.52) values found when the para substituent on the benzene ring of the substrate is altered indicate there is very little charge on the α-carbon in the transition state. The large, constant secondary α-deuterium KIEs of 1.089 ± 0.002 and the large chlorine leaving group KIEs of 1.0076, 1.0074, and 1.0078 found for the p -methyl-, the p -hydrogen-, and the p -chlorobenzyl chloride reactions suggest that the transition states for these reactions are unsymmetric with short H−C α and long B−Η and C α −Cl bonds. The decrease in the chlorine leaving group KIE from 1.0076 ± 0.0003 for the p -methylbenzyl chloride reaction to 1.0036 ± 0.0003 for the p -nitrobenzyl chloride reaction indicates the C α −Cl bond shortens markedly when a strongly electron-withdrawing substituent is on the α-carbon. Unfortunately, the bond strength hypothesis is the only theory that predicts the changes observed in transition-state structure and it only indicates the bond that changes but not how the transition-state structure is altered.
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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 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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".