Stereoelectronic and Resonance Effects on the Rate of Ring Opening of <i>N</i>-Cyclopropyl-Based Single Electron Transfer Probes
Bibliographic record
Abstract
N -Cyclopropyl- N -methylaniline ( 5 ) is a poor probe for single electron transfer (SET) because the corresponding radical cation undergoes cyclopropane ring opening with a rate constant of only 4.1 × 10 4 s –1, too slow to compete with other processes such as radical cation deprotonation. The sluggish rate of ring opening can be attributed to either (i) a resonance effect in which the spin and charge of the radical cation in the ring-closed form is delocalized into the phenyl ring, and/or (ii) the lowest energy conformation of the SET product ( 5 •+ ) does not meet the stereoelectronic requirements for cyclopropane ring opening. To resolve this issue, a new series of N -cyclopropylanilines were designed to lock the cyclopropyl group into the required bisected conformation for ring opening. The results reveal that the rate constant for ring opening of radical cations derived from 1′-methyl-3′,4′-dihydro-1′ H -spiro[cyclopropane-1,2′-quinoline] ( 6 ) and 6′-chloro-1′-methyl-3′,4′-dihydro-1′ H -spiro[cyclopropane-1,2′-quinoline] ( 7 ) are 3.5 × 10 2 s –1 and 4.1 × 10 2 s –1, effectively ruling out the stereoelectronic argument. In contrast, the radical cation derived from 4-chloro- N -methyl- N -(2-phenylcyclopropyl)aniline ( 8 ) undergoes cyclopropane ring opening with a rate constant of 1.7 × 10 8 s –1, demonstrating that loss of the resonance energy associated with the ring-closed form of these N -cyclopropylanilines can be amply compensated by incorporation of a radical-stabilizing phenyl substituent on the cyclopropyl group. Product studies were performed, including a unique application of EC–ESI/MS (Electrochemistry/ElectroSpray Ionization Mass Spectrometry) in the presence of 18 O 2 and H 2 18 O to elucidate the mechanism of ring opening of 7 •+ and trapping of the resulting distonic radical cation.
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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 | 0.001 |
| 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".