Gas-Phase Oligomerization of Propene Initiated by Benzene Radical Cation
Bibliographic record
Abstract
Initiation of the radical cation polymerization of propene has been observed following the selective ionization of benzene in the gas phase by resonance two-photon ionization−high-pressure mass spectrometry (R2PI−HPMS) and by selected ion flow tube (SIFT) techniques. In this system, the aromatic initiator (C 6 H 6 ) has an ionization potential (IP) between those of the reactant's monomer (C 3 H 6 ) and its covalent dimer (C 6 H 12 ), i.e, IP(C 3 H 6 ) > IP(C 6 H 6 ) > IP(C 6 H 12 ). Therefore, direct charge transfer from C 6 H 6 •+ to C 3 H 6 is not observed due to the large endothermicity of 0.48 eV, and only the adduct C 6 H 6 •+ (C 3 H 6 ) is formed. However, coupled reactions of charge transfer with covalent condensation are observed according to the overall process C 6 H 6 •+ + 2C 3 H 6 → C 6 H 12 •+ + C 6 H 6, which results in the formation of a hexene product ion, C 6 H 12 •+ . The formation of this ion can make the overall process of charge transfer and covalent condensation significantly exothermic. At higher concentrations of propene, the reaction products are the propene oligomers (C 3 H 6 ) n •+ with n = 2−7 and the adduct series C 6 H 6 •+ (C 3 H 6 ) n with n ≤ 6. The significance of the coupled reactions is that the overall process leads exclusively to the formation of the condensation product (C 3 H 6 ) n •+ and avoids other competitive channels in the ion/molecule reactions of propene. Gas-phase nominal second-order rate coefficients for the overall reaction into both channels are in the range of (1−3) × 10 -12 cm 3 s -1 . The rate coefficients into both channels, especially for the formation of the C 6 H 12 •+ dimer, have large negative temperature dependencies. Consistent with the gas-phase results, the intracluster reactions of C 6 H 6 •+ produced selectively by R2PI of mixed benzene/propene clusters also do not form the monomer ion C 3 H 6 •+ but form higher propene clusters (C 3 H 6 ) n •+ that contain at least the C 6 H 12 •+ hexene ion. The similarity of the reaction mechanisms in the gas phase and in preformed clusters suggests that the mechanism may also apply in the condensed phase in common aromatic solvents such as benzene and toluene.
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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".