Assessing the impact of anion–π effects on phenylalanine ion structures using IRMPD spectroscopy
Bibliographic record
Abstract
The gas-phase structures of two halide-bound phenylalanine anions (PheX(-), X = Cl(-) or Br(-)) and five fluorinated derivatives have been identified using infrared multiple photon dissociation (IRMPD) spectroscopy. The addition of electron-withdrawing groups to the aromatic ring creates a π-acidic system that additionally stabilizes the halide above the ring face. Detailed ion structures were determined by comparing the IRMPD spectra with harmonic and anharmonic infrared spectra computed using B3LYP/6-311++G(d,p) as well as with 298 K enthalpies and Gibbs energies determined by the MP2(full)/6-311++G(2d,2p)//B3LYP/6-311++G(d,p) and MP2(full)/aug-cc-pVTZ//B3LYP/6-311++G(d,p) methods. PheX(-) structures were found to be dependent on both the nature of the anion and the extent of ring fluorination. Canonical isomers were established to be the dominant structures in every case, but halide addition significantly narrowed the energy gap with zwitterionic potential energy surfaces. This enabled zwitterions to appear as minor contributors to the gas-phase populations of Phe35F2Cl(-) and PheF5Br(-).
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".