Proton and metal‐ion activation of C–H exchange in five‐membered azoles
Bibliographic record
Abstract
Abstract Factors influencing C–H isotopic exchange rates in five‐membered azoles, that is imidazoles and thiazoles, under catalysis by H + and M n + , especially transition metals, Pt(II) and Co(III) are discussed. Hydrogen ion catalysis through N(3) protonation of azoles 1–3 is generally the most efficient, with rate enhancements in the range 10 2 –10 9 over the neutral process being attained. Metal‐ion coordination also results in effective catalysis, though less so than catalysis by protons. Catalysis of C–H exchange by M n + can be studied through addition of the metal salts to a buffered solution of the heterocycle in which labile complexes exist, or on synthesized complexes such as 4–13 which are substitution‐inert thus precluding complications from unknown dissociation equilibria. A delicate balance of factors influence the ease of C–H exchange, including: (1) the magnitude of the fractional charge located at N(3) of the heterocycle through M n + –N(3) σ bond polarization; (2) metal‐to‐ligand π back‐bonding; (3) the electronic structure of the metal ions. These considerations have obvious consequences for deuterium‐ and tritium‐labelling of a number of biomolecules, e.g. proteins, enzymes, nucleic acids, some vitamins, as well as drugs which incorporate five‐membered azoles in their structures. Copyright © 2002 John Wiley & Sons, Ltd.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 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".