Bibliographic record
Abstract
The Norrish/Yang type II photochemistry of sixteen ketones has been studied in the crystalline state as well as in solution. In both media, the ketones, for the most part, undergo stereoselective cyclobutanol formation in which the cis-stereochernistry is produced exclusively. The reactive γ-hydrogen atoms are identified and the distance and angular parameters associated with their abstractions are derived from crystallographic data. Four of the sixteen ketones were found to be photochemically inert as a result of their 1,4-biradical intermediates being poorly aligned for cleavage and also as a result of an excessive distance between the radical centres. The chiral ionic auxiliary concept was shown to be useful for inducing asymmetric induction in solid state photochemistry. Chiral crystals from prochiral carboxyJic acids and optically pure amines were made (seventeen in total), and solid state photolyses of these salts afforded cyclobutanol photoproducts in optically active form (10% to 100% ee). Solid state structure-reactivity relationships are discussed based on X-ray crystal structures of the starting chiral salts. Due to the ionic character of the salts described above, they tend to have strong lattice forces and relatively high melting points. These "natural" two-component crystalline materials proved to be more robust than purely molecular crystals and survived photolysis to higher conversions without loss of topochemical control. In this thesis, we report the first example of a topotactic, enantioselective solid state photorearrangement that involves an ionic chiral auxiliary of known absolute configuration, so that X-ray diffraction studies allowed mapping of the absolute steric course of the photochemical reaction. This was accomplished by obtaining an X-ray crystal structure of the same single crystal at the beginning, midpoint and final stages of reaction. The results of asymmetric induction studies of the Norrish type II photoreaction conducted within zeolites are also presented in this thesis. The results show that zeolites, when modified with chiral inductors, yield photoproducts with low to moderate enantiomeric excess.
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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) | 0.000 | 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".