C−H···X Hydrogen Bonds of Acetylene, Ethylene, and Ethane with First- and Second-Row Hydrides
Bibliographic record
Abstract
The structures and binding energies of a series of C−H···X hydrogen-bonded complexes involving acetylene, ethylene, and ethane as proton donors and the first- and second-row hydrides CH 4, NH 3, OH 2, FH, PH 3, SH 2, and ClH as proton acceptors have been determined. Geometries were optimized with both the MP2 and the B3-LYP methods in conjuction with the 6-311+G(3df,2p) basis set. In general, we note good agreement between MP2 and B3-LYP hydrogen-bonded structures. However, for some very weakly bound complexes larger differences exist, particularly in the r (H···X) distance, and in these instances the MP2 results are determined (from comparative CCSD(T) calculations) to be more reliable. The CCSD(T)/6-311+G(3df,2p) binding energies ( D e ), which include corrections for basis set superposition errors, are very similar for the MP2 and B3-LYP geometries, reflecting the relative insensitivity of D e to geometry for weakly bound complexes. The C−H···X hydrogen-bond strength ( D 0 ) shows a considerable dependence on the acidity of the C−H donor group and on the nature of the proton-accepting group. The strongest hydrogen bonds are formed between acetylene and either NH 3 (9.2 kJ mol -1 ) or OH 2 ( 7.7 kJ mol -1 ). These values decrease significantly for the corresponding complexes between acetylene and FH, CH 4 or the second-row hydrides. The binding energies for the complexes between ethylene and either NH 3 or OH 2 (2.1 and 1.5 kJ mol -1, respectively) are much smaller than those of the corresponding acetylene complexes. The complexes between ethylene and PH 3, SH 2 or ClH, as well as the complexes between ethane and NH 3 or H 2 O, are more weakly bound again and have binding energies less than 1.0 kJ mol -1 .
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".