Toward Identification of Molecules in Ill-Defined Hydrocarbons Using Infrared, Raman, and Nuclear Magnetic Resonance (NMR) Spectroscopy
Bibliographic record
Abstract
The molecular composition of heavy oil and bitumen is critical for process design calculations and for the selection of production and refining processes, reaction schemes, and conditions that optimize their economic value. These materials remain ill-defined on a molecular basis. For example, diverse molecular structures have been proposed for asphaltenes on the basis of the same physical samples and analytical data [ 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy, and elemental composition]. Molecule construction algorithms appear under constrained by these analytical data, particularly at the molecular subunit length scale (e.g., naphthenic and aromatic groups and aliphatic chains) from both an identification and a mass balance perspective. In this work, we address whether spectral data can provide additional constraints at this length scale that reduces the ambiguity of outcomes from molecule construction algorithms, by making use of spectral data for possible subunits. In this proof of concept investigation, infrared (IR), Raman, and 1 H and 13 C NMR spectra were computed using density functional theory (DFT) and the B3LYP/6-311G basis set. The molecular subunits present in more than 20 large molecules were probed by spectral subtraction based on spectral contributions from a library of small molecules, because it is at this length scale that the greatest uncertainty in molecule identification and construction algorithms appears to arise. Spectral subtraction using 1 H NMR spectroscopy failed to identify molecular subunits in any of the more than 20 large molecules evaluated. 13 C NMR spectroscopy identified only 3 large molecules. In contrast, joint use of IR and Raman spectroscopy identified more than 75% of the aromatic subunits present, and naphthenic and aromatic subunits were discriminated. Aliphatic chain length remained poorly defined, and the resulting molecule compositions are qualitative. It is expected that the results of this work will inform molecule construction and identification algorithms for ill-defined hydrocarbons.
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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 | 0.002 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.003 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".