Some Like It Hot: Experimentally Determining ΔΔ<i>H</i><sup>⧧</sup>, ΔΔ<i>S</i><sup>⧧</sup>, and ΔΔ<i>G</i><sup>⧧</sup> between Kinetic and Thermodynamic Diels–Alder Pathways Using Microwave-Assisted Synthesis
Bibliographic record
Abstract
The effects of kinetic vs thermodynamic control on endo / exo stereoisomer ratios can be observed in a simple Diels–Alder reaction between N -phenylmaleimide and furan. The use of microwave-promoted synthesis affords the cycloadducts in yields ranging from 65–100%, employing reaction times of 1–10 min at temperatures of 55–130 °C. Short reaction times enable screening of numerous reaction conditions (time and temperature) within a single lab period, where e ndo: exo product ratios follow the primary facets of kinetic and thermodynamic control. Analysis of product ratios obtained under kinetic control allows for the evaluation of activation parameters (ΔΔ H ⧧ (≈ Δ E a ), ΔΔ S ⧧, and ΔΔ G ⧧ ) by means of the Arrhenius and Eyring equations. Values of ΔΔ H ⧧, ΔΔ S ⧧, and ΔΔ G ⧧ were found to be 6.4 ± 0.3 kJ mol −1, 16.5 ± 0.9 J mol −1 K −1, and 1.5 ± 0.4 kJ mol –1 (ΔΔ: exo – endo ), respectively. Experimentally determined activation parameters correlate well with quantum-chemical calculations. Several key teaching points are also addressed, including frontier molecular orbital analysis, reversibility of the Diels–Alder reaction, column chromatography, and the use of 1 H nuclear magnetic resonance spectroscopy to assess both stereoisomeric yield and purity.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.005 | 0.002 |
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".