Raman Spectra of Persistent Radical Anions from Benzophenone, Fluorenone, 2,2′-Bipyridyl, 4,4′-Di-<i>tert</i>-butyl-2,2′-dipyridyl, and Anthracene: Excellent Agreement between DFT and Experiment for Highly Delocalized Radical Systems
Bibliographic record
Abstract
We report detailed Raman spectra for the neutral and radical anion forms of benzophenone, fluorenone, 2,2′-bipyridyl, 4,4′-di- tert -butyl-2,2′-dipyridyl, and anthracene. Density functional theory (DFT) predictions for the Raman spectra of these molecules give additional insight into the assignment of each vibrational mode. While the use of DFT has been problematic in quantifying the thermochemistry of highly delocalized radicals, we find that DFT-predicted spectra using the popular B3LYP functional are in excellent agreement with the observed Raman spectra. In the case of the two bipyridyl compounds, the Raman spectra allowed us to conclude that the cis form of the radical anion complexed to a sodium cation was the preferred configuration. Benzophenone and fluorenone radical anions gave a significantly weakened C═O bond stretching vibrational frequency as expected from the population of an antibonding π* orbital. For benzophenone, the C═O vibration dropped from 1659 to 1403 cm –1 upon reduction. Similarly, fluorenone showed a C═O vibration observed at 1719 cm –1 for the neutral form that decreased to 1522 cm –1 for the radical anion. The structurally rigid anthracene showed relatively smaller Raman band shifts upon single-electron reduction as the π* orbital is more equally delocalized on the entire structure. In total, we correlated 65 DFT-predicted vibrational modes for the neutral molecules with an overall error of 7.1 cm –1 (root-mean-square errors (RMSEs)) and 67 DFT-predicted vibrational modes for radical anions with an overall error of 9.9 cm –1 . These comparisons between theory and experiment are another example to demonstrate the power of DFT in predicting the identity and geometry of molecules using Raman spectroscopy.
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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 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".