Bimodal Evans−Polanyi Relationships in Hydrogen Atom Transfer from C(sp3)--H Bonds to the Cumyloxyl Radical. A Combined Time-Resolved Kinetic and Computational Study
Bibliographic record
Abstract
The applicability of the Evans-Polanyi (EP) relationship to HAT reactions from C(sp3)-H bonds to the cumyloxyl radical (CumO) has been investigated. A consistent set of rate constants kH, for HAT from the C-H bonds of 56 substrates to CumO, spanning a range of more than four orders of magnitude, has been measured under identical experimental conditions. A corresponding set of consistent gas-phase C-H BDEs spanning 26 kcal/mol has been calculated using the (RO)CBS-QB3 method. The log kH vs C-H BDE plot shows two distinct EP relationships, one for substrates bearing benzylic and allylic C-H bonds (unsaturated group) and the other one, with a steeper slope, for saturated hydrocarbons, alcohols, ethers, diols, amines and carbamates (saturated group), in line with the bimodal behavior observed previously in theoretical studies of reactions promoted by other HAT reagents. The parallel use of BDFEs instead of BDEs allows the transformation of this correlation into a linear free energy relationship, analyzed within the framework of the Marcus theory. The ΔG‡ HAT vs ΔG°HAT plot shows again distinct behaviors for the two groups. A good fit to the Marcus equation is observed only for the saturated group, with lambda = 58 kcal mol-1, indicating that with the unsaturated group lambda must increase with increasing driving force. Taken together these results provide a qualitative connection between Bernasconi’s Principle of Nonperfect Synchronization and Marcus theory and suggest that the observed bimodal behavior is a general feature in the reactions of oxygen-based HAT reagents with C(sp3)-H donors.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".