A general measure of conjugation in biphenyls and their radical cations
Bibliographic record
Abstract
Changes in the amount of conjugation in the biphenyl system upon torsion have been investigated with quantum chemistry computations. For the unsubstituted biphenyl and its radical cation, the change in the energy for the first electronic transition as determined from time-dependent density functional theory, specifically TD-B3LYP, upon an imposed change in torsion angle appears to provide a good general measure of the delocalization of the π-electrons. Upon substitution, though, a relationship could not be established between the excitation energy and the twist across the C–C bond connecting the two phenyl rings. In contrast, the π-interaction energy, i.e., the π–π interaction across the central C–C bond, determined from a natural bond orbital analysis, provides a uniform description of conjugation in the electronically different systems, for an imposed twist as well as upon substitution. Substituent effects are found to be larger and more varied for the biphenyl radical cations. Of particular interest is the introduction of the oxidizable substituents OCH3 (methoxyl) and SCH3 (methylthio), as this leads to the smallest changes in torsion angle in the biphenyl unit upon removal of an electron from the molecule. The findings of this work could ultimately prove useful for the rational design of conductive polymer materials.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".