Metal ion promoted transesterifications of carboxylate esters. A structure/activity study of the efficacy of Zn2+ and La3+ to catalyze the methanolysis of some aryl and aliphatic esters
Bibliographic record
Abstract
The methanolysis of various aryl and aliphatic carboxylate esters promoted by methoxide, 1,5,9-triazacyclododecane : Zn2+(-OCH3) and La3+(-OCH3), were studied and the derived rate constants (kOCH3, kcat3:Zn(OCH3) and kcatLa(OCH3)) correlated in various ways. The metal ion catalyzed reactions are very much faster than the background reactions in some cases reaching up to 7 x 10(6)-fold acceleration when present at concentrations of 5 mmol dm(-3). The data for both metals exhibit non-linear Bronsted correlations with the pKa of the leaving group which are analyzed in terms of a change in rate limiting step from formation to breakdown of a metal-coordinated tetrahedral intermediate as the pKa increases above values of approximately 14.7. Plots of the log kOCH3 reaction vs. the log kcat values for each metal ion indicate low sensitivity for aryl esters and a higher sensitivity for the aliphatic esters. A mechanistic rationale for the observations is presented.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 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 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".