A Quantitative Scale for the Degree of Aromaticity and Antiaromaticity: A Comparison of Theoretical and Experimental Enthalpies of Hydrogenation
Bibliographic record
Abstract
Chemical structures and transition states are often influenced by aromatic stabilization or antiaromatic destabilizing effects, which are not easy to characterize theoretically. The exact description and precise quantification of the aromatic characteristics of ring structures is difficult and requires special theoretical investigation. The present paper suggests a novel, yet simple, method to quantify both aromatic and antiaromatic qualities on the same linear scale, by using the experimentally measured or theoretically computed enthalpy of hydrogenation reaction of the compound examined [DeltaHH2(examined)]. A reference hydrogenation reaction is also considered on a corresponding nonaromatic reference compound [DeltaHH2(reference)] to cancel all secondary structure destabilization factors, such as ring strain or double bond strain. From these data the relative enthalpy of hydrogenation may easily be calculated: DeltaDeltaHH2=DeltaHH2(examined)-DeltaHH2(reference). In the present work concept, the DeltaDeltaHH2 value of benzene defines the completely aromatic character (+100%), and the closed shell of the singlet cyclobutadiene represents maximum antiaromaticity (-100%). The component DeltaHH2 values were computed at different levels of theory offering a computational "method-independent" measure for aromaticity. A total of 28 well-known aromatic, antiaromatic and nonaromatic, neutral and charged compounds were examined to demonstrate the efficiency of this methodology. Finally, a correlation was made between the calculated aromaticity percentage of the compound examined and their popular Schleyers NICS values.
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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 | 0.002 |
| 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) | 0.002 | 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".