Conformational Study of a Bent-Core Liquid Crystal: <sup>13</sup>C NMR and DFT Computation Approach
Bibliographic record
Abstract
A detailed conformational study is carried out by means of density functional theory (DFT) on a bent-core mesogen (A131) in order to shed light on its uniaxial-biaxial nematic phase transition. The most probable conformational states for this V-shaped core are found, from the potential energy surface (PES) of a five-ring model of A131, to fall into two distinct structural groups, namely, the banana-shaped and the hockey-stick-shaped forms. The chemical shielding tensors (CSTs) of the aromatic carbons, for the four prevalent conformers, have been calculated using the GIAO-DFT approach. The derived CSTs are found to compare well with the chemical shift anisotropy (CSA) tensors measured by the 2D-NMR SUPER technique. The CSA tensors are then used to aid the assignment of the aromatic carbon peaks, and the observed (13)C chemical shifts from its nematic phases are revisited to provide new structural and local orientational order parameters. In light of the conformational states found from the in vacuo DFT calculations, the "average" configuration shapes of the A131 molecule are found to be different in the nematic phases based on their new local order parameters S and D of the aromatic rings.
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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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".