C2-Oxyanion Neighboring Group Participation: Transition State Structure for the Hydroxide-Promoted Hydrolysis of 4-Nitrophenyl α-<scp>d</scp>-Mannopyranoside
Bibliographic record
Abstract
High Resolution Image Download MS PowerPoint Slide The hydroxide-catalyzed hydrolysis of aryl 1,2- trans -glycosides proceeds through a mechanism involving neighboring group participation by a C2-oxyanion and rate-limiting formation of a 1,2-anhydro sugar (oxirane) intermediate. The transition state for the hydroxide-catalyzed hydrolysis of 4-nitrophenyl α- d -mannopyranoside in aqueous media has been studied by the use of multiple kinetic isotope effect (KIE) measurements in conjunction with ab initio theoretical methods. The experimental KIEs are C1- 2 H (1.112 ± 0.004), C2- 2 H (1.045 ± 0.005), anomeric 1- 13 C (1.026 ± 0.006), C2- 13 C (0.999 ± 0.005), leaving group oxygen 2- 18 O (1.040 ± 0.012), and C2- 18 O (1.044 ± 0.006). The transition state for the hydrolysis reaction was modeled computationally using the experimental KIE values as constraints. Taken together, the reported kinetic isotope effects and computational modeling are consistent with the reaction mechanism involving rate-limiting formation of a transient oxirane intermediate that opens in water to give α- d -mannopyranose. The transition state has significant nucleophilic participation by the C2-alkoxide, an essentially cleaved glycosidic bond, and a slight shortening of the endocyclic C1–O5 bond. The TS is late, consistent with the large, normal C2- 18 O isotope effect.
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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) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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".