Theoretical and experimental investigations in chemistry: Part 1- SN2 Reactivity at C-6 in hexopyranosides, Part 2- Polarizability and raman intensities in hydrocarbons
Bibliographic record
Abstract
In this thesis, two rather different types of problems were investigated.\nThe first was a case of anomalous reactivity in the area of carbohydrate synthesis.\nHexopyranosides having the galacto configuration (i.e. C-4?OR axial) display\nvery low SN2 reactivities towards anionic nucleophiles, whereas the\ncorresponding gluco-configured C-6 sulfonates (C-4?OR equatorial) react at rates\ntypical of primary centers. The accepted explanation for this difference involves\nthe repulsive interaction of local dipoles in the transition structure of the galacto\ncompound. This interaction is thought to destabilize the transition structure,\nmaking this reaction difficult. However, there are numerous inconsistencies in\nthe application of this simple model (cases where the model fails to predict the\nobserved behavior). Thus, a computational project was undertaken to examine six\nmodel systems of this type. The energetics and equilibria of the reactants were\ndetermined, including solvation. Reaction pathways and kinetics for various\ndisplacements were computed. Analyses of the calculated charge densities\nallowed for evaluation of any electrostatic interactions. This study revealed a\nnumber of important factors affecting the rates of reaction, while clearly showing\nthat dipole-dipole interactions are very limited in these systems.\nThe second project was in the related areas of molecular polarizability and\nvibrational spectroscopy. Descriptive models have been sought relating the\nstructure and connectivity of molecules to their electronic properties. Researchers\nin the areas of non-linear optics and of conducting polymers require a better\nunderstanding of the effects of structural variations on electronic properties. The\n4\nsimplest models of molecular polarizability and its derivatives with respect to\nmolecular vibrations are grossly inadequate. The highest-level calculations are\ngenerally reliable but are not applicable to even moderately sized systems. Thus\ntrends in these properties were investigated for a large series of molecules.\nCalculations were performed at a variety of theoretical levels in order to\ndetermine the ranges of predicted behavior. Since these calculations predicted\nunusual properties in bicyclo-[1.1.1]-pentane, an experimental project was\ncompleted on this molecule. The results of Raman scattering intensity\nexperiments on bicyclo-[1.1.1]-pentane allowed for evaluation of the performance\nof various computational methods. More importantly, it allowed for the\nconfirmation of some qualitative structure/property relationships.
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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 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.009 | 0.001 |
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".