Gas-phase basicities of polyfunctional molecules. Part 2 : saturated basic sites

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Modelling of spectroscopic and structural properties using molecular dynamics

The work described here was carried out at the European Lab. for Non-Linear Spectroscopy (LENS) to achieve a better understanding of molecular vibrations employing computer simulations. H-bonds are the main intermolecular interactions affecting vibrational spectra and here it’s shown how they usually induce a (red or blue) shift on the vibrational frequencies of the groups engaged in them, and how this shift nicely correlates with structural properties. H-bonds can be present also in a bifurcated arrangement. In systems such as confined water, this bifurcated configuration has long lifetimes, allowing it to be studied by both spectroscopic and computational means. The computational protocols implemented and adopted here allow for a direct comparison between structural features and vibrational spectra

Intramolecular Hydrogen Bonding 2021

This book describes the results of both theoretical and experimental research on many topical issues in intramolecular hydrogen bonding. Its great advantage is that the presented research results have been obtained using many different techniques. Therefore, it is an excellent review of these methods, while showing their applicability to the current scientific issues regarding intramolecular hydrogen bonds. The experimental techniques used include X-ray diffraction, infrared and Raman spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), nuclear quadrupole resonance spectroscopy (NQR), incoherent inelastic neutron scattering (IINS), and differential scanning calorimetry (DSC). The solvatochromic and luminescent studies are also described. On the other hand, theoretical research is based on ab initio calculations and the Car–Parrinello Molecular Dynamics (CPMD). In the latter case, a description of nuclear quantum effects (NQE) is also possible. This book also demonstrates the use of theoretical methods such as Quantum Theory of Atoms in Molecules (QTAIM), Interacting Quantum Atoms (IQA), Natural Bond Orbital (NBO), Non-Covalent Interactions (NCI) index, Molecular Tailoring Approach (MTA), and many others

Studies in Photochemistry, Hydration, and Diversity in Chemistry: Shining a Light on Sulfur Dioxide and the Effects of Gender and Sexuality on Belonging in Introductory Chemistry

In this thesis I investigate the role of sunlight as a potential driver of the formation of sulfur-containing aerosols. The reaction of electronically excited sulfur dioxide (3SO2) with water and alkanes results in the formation of aerosol. Using a combination of laboratory and computational studies I show that reaction of&nbsp;3SO2&nbsp;with water can proceed via two pathways, hydration to form sulfurous acid (H2SO3) or hydrogen abstraction from the water to form HOSO&bull; and OH&bull;. I additionally show that reaction of&nbsp;3SO2&nbsp;with alkanes (RH) proceeds via hydrogen abstraction to initially form HOSO and R&bull; and is a function of the number of CH2 groups in the molecule. I also investigate the hydration of gas phase methylglyoxal and hydrogen bonding in methyl lactate. I find that upon hydration, the electronic states of the molecule are significantly affected, changing the wavelengths of ultraviolet light absorbed by the molecule. This likely has an impact on the chemical fate of methylglyoxal in the atmosphere. Using methyl lactate as a test molecule, I show that intramolecular hydrogen bonding to carbonyl oxygen atoms is stronger than that to ester oxygen atoms. This provides insight into the hydrogen bonds that may be forming in the atmosphere and better understanding of how those molecules will behave. In addition to my research in the chemical laboratory, I have performed a survey study investigating ability uncertainty and social belonging in introductory chemistry. This is the first broad survey of students in STEM to determine if LGBTQ+ students are underrepresented. I find that LGBTQ+ students are not underrepresented compared to the university general population and account for ~10% of the students enrolled in General Chemistry I. I find no statistically significant differences between any group of students based on gender or sexuality. However, the strong correlation of grade with ability uncertainty may be confounding my ability to measure differences.</p

Part I: The Confluence of Steric and Electronic Effects in N-Heterocyclic Carbene-Catalyzed Processes Part II: Studies Toward the Asymmetric Oxidative Coupling of Phenols

The N-heterocyclic carbene catalyzed hetero-Diels-Alder cycloadditions of α,β-unsaturated enones with NHC-enolate adducts generate γ,δ-unsaturated δ-lactones in high yield and enantioselectivity. A quantitative structure-activity relationship analysis of experimental results using a series of NHC ligands reveals a strong correlation between selectivity and steric and electronic parameters. The stereoselectivity-determining step is determined to proceed through a concerted, asynchronous, zwitterionic hetero-Diels-Alder cycloaddition rather than a Michael addition or Claisen rearrangement. A transition state model is developed that accurately predicts the experimental results. A CH–π interaction acting in concert with an anion-π interaction is determined to be the cause of observed electronic effect. The steric contribution is derived from steric clashes between the catalyst and the approaching enone. The N-heterocyclic carbene and hydroxamic acid co-catalyzed kinetic resolution of secondary cyclic amines developed by the Bode lab furnishes enantioenriched amides and amines with selectivity factors up to 74. A mechanism study revealed that the reaction proceeds through a novel hydroxamic acid proton transfer modification of the concerted aminolysis pathway. Systematic analysis of transition state conformations revealed the steric effects that lead to the observed selectivity. The transition state model developed predicted the observed selectivity factors for two hydroxamic acid esters. Part II. The asymmetric oxidative coupling of phenols remains a significant challenge in organic chemistry. Binuclear oxovanadium amino acid Schiff base catalysts developed by Gong and Sasai for naphthol coupling were determined to be batch-dependent when applied to phenol coupling. Optimization of catalyst preparation diminished this problem. Amino ester Schiff base catalysts allowed for in situ complex formation and improved selectivities at the expense of conversion. Novel BINOL-like scaffolds failed to improve the selectivity in the phenol coupling reaction. A series of tethered catalysts ultimately led to the identification of monomeric catalysts that can produce chiral bisphenols in high yield and moderate enantioselectivity

Experimental and theoretical investigation of nucleation and growth of atmospheric aerosols

Aerosol particles have profound impacts on human health, atmospheric radiation, and cloud microphysics and these impacts are strongly dependent on particle sizes. However, formation and growth of atmospheric particles are currently not well understood. In this work, laboratory and theoretical studies have been performed to investigate the formation and growth of atmospheric particles. The first two parts of the dissertation are a laboratory investigation of new particle formation and growth, and a theoretical study of atmospheric molecular complexes and clusters. The nucleation rate was considerably enhanced in the presence of cis-pinonic acid and ammonia. The composition of the critical cluster was estimated from the dependence of the nucleation rate on the precursor concentration and the time evolution of the clusters was then simulated using molecular dynamic simulations. Results from quantum chemical calculations and quantum theory of atoms in molecules (QTAIM) reveal that formation of strong hydrogen bonding between an organic acid and sulfuric acid is likely responsible for a reduction of the nucleation barrier by modifying the hydrophobic properties of the organic acid and allowing further addition of hydrophilic species (e.g., H2SO4, H2O, and possibly NH3) to the hydrophilic side of the clusters. This promotes growth of the nascent cluster to overcome the nucleation barrier and thus enhances the nucleation in the atmosphere. The last part of this dissertation is the laboratory investigation of heterogeneous interactions of atmospheric carbonyls with sulfuric acid. Direct measurement has been performed to investigate the heterogeneous uptake of atmospheric carbonyls on sulfuric acid. Important parameters have been obtained from the time-dependent or timeindependent uptake profiles. The results indicated that the acid-catalyzed reactions of larger aldehydes (e.g. octanal and 2, 4-hexadienal) in sulfuric acid solution were attributed to aldol condensation in high acidity. However such reactions do not contribute much to secondary organic aerosol (SOA) formation due to the low acidity under tropospheric conditions. On the other hand, heterogeneous reactions of light dicarbonyl such as methylglyoxal likely contribute to SOA formation in slightly acidic media. The reactions of methylglyoxal in the atmospheric aerosol-phase involve hydration and subsequent polymerization, which are dependent on the hygroscopicity, rather than the acidity of the aerosols

Pyrazolone-based metal complexes: synthesis, characterization and theoretical study of Zn(II), Cu(II) and Mo(IV) derivatives

4-acyl-5-pyrazolones are a class of compounds that combine the properties of the pyrazolone ring with that of diketones, affording an O,O-chelating ligand with biological features. Since the first synthesis by Jensen in 1959 they have been the subject of a multitude of studies concerning their tautomeric forms, their biological properties, and their coordination chemistry towards a variety of metal centres. Furthermore, the readiness of the structural modifications they can undergo pushed researchers to explore many different variations tailoring the substituents to optimize their coordination with the metals and to vary their properties. In particular, one interesting variant of 4-acyl-5-pyrazolones is obtained by condensation with hydrazine or amine to afford N,O-chelating Schiff base ligands. This class of ligands retains all the characteristics of their synthon and additionally, they show enhanced coordination features due to the presence of one or more nitrogen atoms. In Chapter 1 an introduction to these compounds is reported together with a comprehensive state-of-the-art of their metal complexes, involving zinc, copper, and molybdenum. Chapter 2 deals with the synthesis and characterization of Schiff base ligands and the study of their tautomerism in solid state and solution. The ligands have then been utilized to synthesize the respective zinc(II) complexes of composition [Zn(HLn )2], they were fully characterized and the structures of two ligands and three complexes were determined by X-ray diffraction, showing that complexes 1 and 2 have a monomeric nature, while complex 4 exists as one-dimensional coordination polymer. DFT calculations on proligands, anions and complexes were exploited to confirm the experimental result and rationalized the polymeric nature of complex 4 and the presence of two water molecules coordinated on complexes 3 and 5. The antimicrobial activity of the compounds was investigated against Escherichia coli and Staphylococcus aureus. Complexes 4 and 5 demonstrated good efficiency, the latter probably for its ligand containing aliphatic and fluorinated substituents. Similarly, in Chapter 3 two hydrazone ligands were synthesized, characterized and reacted with Zn(II) and Cu(II) affording four complexes of formula [Zn(HL1 )2(MeOH)2], [Cu(HL1 )2], and [M(HL2 )2]. DFT and XRD studies determined that the free proligands exist in the NH,NH tautomeric form, [Zn(HL1 )2(MeOH)2] has an octahedral geometry with two apical methanol molecules, [Cu(HL1 )2] adopts a square planar geometry, and the two [M(HL2 )2] are octahedral with the ligands acting as tridentate O,N,N-donors in planar conformation. All the compounds were tested against the parasite Trypanosoma brucei and Balb3T3 cells obtaining powerful results, from the ligand H2L 1 and its Zn complex, showing a high selectivity index. For this reason, the mechanism of action of these two compounds has been investigated, indicating a strong impact on the CTP (cytidine triphosphate) pools, making it likely that CTP synthetase is the targeted enzyme. Chapter 4 is focused on the theoretical study of the mechanism of molybdenum-catalyzed deoxydehydration (DODH) of vicinal diols to alkenes. The mechanism has been investigated employing DFT calculations and considering [Mo(O)2(QMe)2] as a catalyst, where QMe is an O,O-donor pyrazolone-based ligand, and PMe3 as a reductant. Two different pathways have been analysed differing in the order of the main steps of the reaction. The lowest energy profiles were calculated for both, and the data obtained suggest that the second pathway is energetically preferred. Finally, In Chapter 5, a list of activities aimed at improving the efficiency of the processes of TechPol srl, a company active in the field of technopolymer molding, is reported. The activities carried out have optimized the use of recycled materials in a circular economy perspective, investigating the nature of the problems encountered and confirming that the main cause was the material used