Geometry and torsional energies of a C–C-protonated <i>n</i>-alkane
Bibliographic record
Abstract
The geometry and relative energies of torsional conformers of centrally protonated C4H11+ were studied with ab initio methods, to (a) obtain the most accurate geometry of the three-center–two-electron CHC bond to date, (b) evaluate the performance of lower levels of approximation upon this challenging structure, and (c) gain an understanding of the torsional dynamics of C4H11+. Twenty-nine combined levels of theory were used to optimize the geometry of the C2-symmetry minimum for trans-C4H11+, and the most accurate one [CCSD(T)/cc-pVTZ] gave the following CHC bond geometry: θCHC=122.4°, RCC=2.177 Å, RCH=1.2424 Å. Molecular-orbital-based methods generally perform better than density functional methods for describing the three-center–two-electron bond. A smaller subset of levels of theory was used to optimize other torsional conformers of centrally protonated C4H11+, varying the CCCC dihedral (trans, gauche, cis) and the dihedral for the bridging proton (various eclipsed and staggered positions). The results show that all conformers lie within a 4 kJ mol−1 range, with the lowest-energy conformer being either trans or gauche with a staggered dihedral for the bridging proton. The effect of core-valence correlation was also investigated. Finally, the potential energy surface as a function of the CCCC and bridging-proton dihedral angles was qualitatively estimated and drawn, based on our computed data, to aid in understanding the fluxional character of C4H11+.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.005 | 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".