The Role of Non-Covalent Interactions in Shaping the Structure of Small Molecular Clusters: Insights from Rotational Spectroscopy and Quantum Chemical Computations
Bibliographic record
Abstract
This thesis explores the role of non-covalent interactions (NCIs) in shaping the conformational landscapes of small organic molecules and molecular clusters, with an emphasis on their influence on cluster formation. These investigations were carried out using a combined experimental and theoretical approach: experimental broadband rotational spectroscopy, complemented by quantum chemical calculations. All experimental rotational spectra were measured using the 2-6 GHz chirped pulsed- Fourier transform microwave (CP-FTMW) instrument at the University of Alberta, which was extended to cover the 2-16 GHz range. NCIs are fundamental in governing how molecular clusters form. Accurately predicting such processes requires a detailed understanding of how NCIs perturb the potential energy surfaces of individual species. In this work, this challenge is addressed through a stepwise approach – beginning with monomeric species, progressing to dimers, and ultimately to higher-order clusters. First, the conformational landscapes of meso- and rac-1,4-pentanediol (PDL), a flexible diol, were explored and multiple conformers were identified for both species. Interesting OH tunneling splittings were detected. By using the Nudged Elastic Band (NEB) analysis, the tunneling barriers and conformational conversion barriers were computed to properly explain the tunneling splittings and the experimental observation or non-observation of low-energy conformers. The study paved the road the future high resolution rotational spectroscopic investigations of larger PDL aggregates with itself and with other fluoroalcohols. A main focal point of this thesis is the study of mono- and dihydrate clusters of 1-phenyl-2,2,2-trifluoroethanol (PhTFE). Results show that the addition of a single water molecule modifies the conformational preferences of PhTFE, enabling experimental detection of a higher-energy conformer (PhTFE II) that is otherwise not observable. Despite this, the global minimum conformer, PhTFE I, remains dominant in the monohydrate complex. Remarkably, when a second water molecule is added, only PhTFE II is observed, suggesting that this conformer becomes more stable under these solvation conditions. This behaviour is rationalized by differences in the stabilizing interactions of each conformer. PhTFE I is stabilized primarily by an intramolecular hydrogen bond between the alcohol hydrogen and fluorine, an interaction that accommodates a single water molecule but becomes destabilized upon the insertion of a second. Conversely, PhTFE II features a broader dispersive interaction between the alcohol hydrogen and the phenyl ring, which can accommodate two water molecules with minimal structural distortion. The final part of the thesis focuses on the experimental identification of the low-energy conformers in various binary and ternary clusters consisting of 2,2,2-trifluoroethanol (TFE) and 1,4-dioxane (Diox). In particular, mixed trimers containing either two TFE subunits and one Diox subunit or one TFE subunit and two Diox subunits were experimentally detected. Notably, the conformer TFE1-Diox2-II was observed, despite not being the lowest energy conformer, underscoring the importance of benchmarking theoretical energy ordering against high-quality conformer-specific experimental data. This work provides new insight into the formation mechanisms of TFE-Diox complexes and brings us closer to understanding the loss of catalytic activity when TFE and 1,4-dioxane are used together as co-solvents.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 teacher head, 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".