Hailiang Zhao

Hydrogen bonding in alcohol–ethylene oxide and alcohol–ethylene sulfide complexes

The hydrogen bonds involving sulfur are generally regarded as weak hydrogen bonds in comparison with conventional ones. The O–H⋯O and O–H⋯S hydrogen bonds in the alcohol–ethylene oxide (EO) and alcohol–ethylene sulfide (ES) complexes in the gas phase have been investigated by FTIR spectroscopy. Three alcohols, methanol (MeOH), ethanol (EtOH) and 2,2,2-trifluoroethanol (TFE) were used as hydrogen bond donors, and comparable OH-stretching red shifts were observed for the complexes with EO and ES as hydrogen bond acceptors. DFT calculations were used to determine the stable structures and interaction energies of the complexes. The equilibrium constant for the complex formation was determined from the experimental integrated absorbance and the computational IR intensity of the OH-stretching transition band of the complex. The effect of CF3 substitution on the hydrogen bond strength in alcohol–EO/ES molecular complexes was investigated and the TFE complexes form much stronger hydrogen bonds than the MeOH and EtOH complexes. Atoms-in-molecules (AIM) analysis revealed that several hydrogen bond interactions were present in the complexes. In addition, the localized molecular orbital-energy decomposition analysis (LMO-EDA) was implemented to analyze the intermolecular interactions. The O–H⋯O and O–H⋯S hydrogen bonds were found to be of similar strength, on the basis of the geometric parameters, binding energies and AIM analysis.

Matrix isolation FTIR study of hydrogen-bonded complexes of methanol with heterocyclic organic compounds

Acting as hydrogen bond acceptors, heterocyclic compounds could interact with a hydrogen bond donor, where either the heteroatom or the π system is the bonding site. The hydrogen bonded complexes of heterocyclic compounds with methanol (MeOH) were studied using matrix isolation FTIR spectroscopy and theoretical calculations based on density functional theory. Four heterocyclic compounds, furan (Fu), 2,5-dihydrofuran (DHF), pyrrole (Py) and thiophene (Th) were selected as representative examples for acceptors. For each of the MeOH–Fu, MeOH–DHF and MeOH–Th complexes, the O–H⋯π and O–H⋯Y (YO, S) hydrogen bonded structures were obtained, while an N–H⋯O instead of O–H⋯N hydrogen bonded conformer was found in the MeOH–Py complex. The measured OH-stretching transitions of the complexes in the IR spectra were assigned to the O–H⋯O bonded MeOH–Fu (b) and MeOH–DHF (b) conformers and the N–H⋯O bonded Py–MeOH (b) conformer, respectively. However, it was hard to assign the spectra to the exact MeOH–Th conformer, because all the hydrogen bond characteristic features obtained for different MeOH–Th conformers are too close. DHF forms a stronger O–H⋯O hydrogen bond than furan, and the O–H⋯O hydrogen bonded MeOH–Fu complex is more stable than the O–H⋯S bonded MeOH–Th complex. Atoms in molecules analysis was also performed to understand the nature of interaction in the MeOH complexes. This analysis allowed us to characterize the new bond critical point generated in the complexes. The present results help to evaluate the atmospheric behavior of some heterocyclic compounds, and indicate their importance in the pre-nucleation mechanism at the molecular level.

Hydrogen Bonding Interaction between Atmospheric Gaseous Amides and Methanol

Amides are important atmospheric organic–nitrogen compounds. Hydrogen bonded complexes of methanol (MeOH) with amides (formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide and N,N-dimethylacetamide) have been investigated. The carbonyl oxygen of the amides behaves as a hydrogen bond acceptor and the NH group of the amides acts as a hydrogen bond donor. The dominant hydrogen bonding interaction occurs between the carbonyl oxygen and the OH group of methanol as well as the interaction between the NH group of amides and the oxygen of methanol. However, the hydrogen bonds between the CH group and the carbonyl oxygen or the oxygen of methanol are also important for the overall stability of the complexes. Comparable red shifts of the C=O, NH- and OH-stretching transitions were found in these MeOH–amide complexes with considerable intensity enhancement. Topological analysis shows that the electron density at the bond critical points of the complexes fall in the range of hydrogen bonding criteria, and the Laplacian of charge density of the O–H∙∙∙O hydrogen bond slightly exceeds the upper value of the Laplacian criteria. The energy decomposition analysis further suggests that the hydrogen bonding interaction energies can be mainly attributed to the electrostatic, exchange and dispersion components.

Hydrogen bonding in cyclic complexes of carboxylic acid–sulfuric acid and their atmospheric implications

The interactions of three common carboxylic acids (glyoxylic acid, oxalic acid and pyruvic acid) with an atmospheric nucleation precursor (sulfuric acid) have been investigated with density functional theory, atoms in molecules and localized molecular orbital energy decomposition analysis methods. A typical feature of the complexes is the formation of cyclic ring systems via two types of hydrogen bonds: SO–H⋯O and CO–H⋯O. Based on the geometric parameters, the SO–H⋯O hydrogen bonds are classified as strong to medium-strength hydrogen bonds, and all the CO–H⋯O hydrogen bonds belong to medium-strength hydrogen bonds. The carboxylic acid–sulfuric acid complexes possess larger binding energies in the nine- and eight-membered rings than in the seven- and six-membered rings. The red shifts of the OH-stretching transitions of both the SO–H⋯O and CO–H⋯O hydrogen bonds are much larger in the nine- and eight-membered rings than those in the seven- and six-membered rings with respect to the isolated monomers. The localized molecular orbital energy decomposition analysis shows that the electrostatic interaction is the major contribution to the total interaction energy. Topological analysis shows that the charge density at the bond critical points of the carboxylic acid–sulfuric acid complexes falls in the range of hydrogen bonding criteria. The Gibbs free energy of formation calculated within the atmospheric temperature and pressure range (atmospheric height 0–12 km) could help to further validate the potential importance in atmospheric particle nucleation and growth.

Theoretical investigation of the hydrogen bond interactions of methanol and dimethylamine with hydrazone and its derivatives

The interactions between hydrogen bond donors (dimethylamine (DMA) and methanol (MeOH)) and acceptors (formaldehyde dimethylhydrazone, acetaldehyde N,N-dimethylhydrazone and N-nitrosodimethylamine) were theoretically investigated by DFT. The hydrogen bonding interactions were found on several bonding sites of the acceptors. The important properties of structure, binding energy, enthalpy of formation, Gibbs free energy of formation and equilibrium constant were investigated. Compared to the monomer, the DMA complexes show a small red shift of the NH-stretching vibrational transition but a significantly intensity enhancement. On the other hand, the MeOH complexes have a large red shift but a relatively small intensity enhancement of the OH-stretching transition. Atoms-in-molecules analysis revealed that several types of hydrogen bond interaction were present in the complexes. Since natural bond orbital analysis overestimated the effect of charge transfer, the more reliable localized molecular orbital energy decomposition analysis was performed and it shows that the major contribution to the total interaction energy is the electrostatic interaction. All these parameters suggest that the hydrogen bond donor strength of MeOH is substantially greater than DMA.

Hydrogen bond docking site competition in methyl esters

The OH⋯O hydrogen bonds in the 2,2,2-trifluoroethanol (TFE)-methyl ester complexes in the gas phase have been investigated by FTIR spectroscopy and DFT calculations. Methyl formate (MF), methyl acetate (MA), and methyl trifluoroacetate (MTFA) were chosen as the hydrogen bond acceptors. A dominant inter-molecular hydrogen bond was formed between the OH group of TFE and different docking sites in the methyl esters (carbonyl oxygen or ester oxygen). The competition of the two docking sites decides the structure and spectral properties of the complexes. On the basis of the observed red shifts of the OH-stretching transition with respect to the TFE monomer, the order of the hydrogen bond strength can be sorted as TFE-MA (119cm-1)>TFE-MF (93cm-1)>TFE-MTFA (44cm-1). Combining the experimental infrared spectra with the DFT calculations, the Gibbs free energies of formation were determined to be 1.5, 4.5 and 8.6kJmol-1 for TFE-MA, TFE-MF and TFE-MTFA, respectively. The hydrogen bonding in the MTFA complex is much weaker than those of the TFE-MA and TFE-MF complexes due to the effect of the CF3 substitution on MTFA, while the replacement of an H atom with a CH3 group in methyl ester only slightly increases the hydrogen bond strength. Topological analysis and localized molecular orbital energy decomposition analysis was also applied to compare the interactions in the complexes.

Selectivity of Cobalt Corrole for CO vs. O 2 and N 2 in Indoor Pollution

Coal combustion causes indoor pollution of CO. In this work, DFT calculations on cobalt corrole (Co(Cor)) with three most common indoor gas molecules (N2, O2 and CO) were performed. The Mulliken spin densities show that the ground states of Co(N2)(Cor), Co(CO)(Cor) and Co(OC)(Cor) have an anti-ferromagnetic coupling fashion of the electrons on the Co 3dz2 orbital and the π orbital of the corrole ring. However, Co(O2)(Cor) has a triplet ground state. With the spin contamination corrections, the Co(N2)(Cor) binding energy was obtained at −50.6 kcal mol−1 (B3LYP-D3). While CO can interact with Co(Cor) in two different ways, and their binding energies were −22.8 and −10.9 kcal mol−1 (B3LYP-D3) for Co(CO)(Cor) and Co(OC)(Cor), respectively. The natural bond orbital charges on the axial ligands (NO, CO, OC) are increased upon the chemical bond formation. These are the cause of the shorten metal-ligand bond and the increase of the wavenumber of the metal-ligand bond vibrational transitions. While the charges for O2 are decreased, leading to bond elongation as well as the decrease of the wavenumber upon complexation. Overall, O2 was found to be hardly coordinated with Co(Cor). This study provides a detailed molecular understanding of interactions between a gas sensor and gaseous indoor air-pollutants.

Molecular understanding of the interaction of methyl hydrogen sulfate with ammonia/dimethylamine/water

Theoretical calculations at the B3LYP-D3/aug-cc-pVTZ (aug-cc-pV(T+d)Z for sulfur) level were used to investigate the contribution of methyl hydrogen sulfate (MHS) to new particle formation with the common atmospheric aerosol nucleation precursors including water (H2O), ammonia (NH3), and dimethylamine (DMA). A typical characteristic feature of the MHS-containing complexes is the formation of six- or eight-membered ring structures via SOH⋯O (MHS donor), OH⋯O/N (H2O donor) and NH⋯O/N (NH3/DMA donor). The stability of the complexes was evaluated based on the calculated binding energies. The molecular interactions between three molecules are found to be more thermodynamically favorable than the complexes consisting two molecules. The red shifts of the SOH-stretching (MHS donor) vibrational transitions with respect to the isolated monomers are much larger than the red shifts of the OH (H2O donor) and NH-stretching (NH3/DMA donor) vibrational transitions. Topological analysis shows that the electron density and Laplacian at the bond critical points beyond the range of hydrogen bonding criteria for most of the complexes. This is due to the strong acid-base interaction between MHS and DMA or NH3, thus leads to a proton transfer from MHS to DMA or NH3. Remarkably, the atmospheric relevance of the MHS-containing complexes is much higher than H2SO4, which is evaluated by combining the calculated thermodynamic data and the concentrations of the reactant species. This study reveals the environmental fate of MHS could serve as nucleation centers in new particle formation.

Weak hydrogen bonding competition between O–H⋯π and O–H⋯Cl

The weak intermolecular interaction between 2,2,2-trifluoroethanol (TFE) and 3-chloro-2-methyl-1-propene (CMP) has been investigated by gas phase FTIR spectroscopy and DFT calculations. CMP offers two hydrogen bond docking sites to the hydrogen bond donor: the chlorine atom (O–H⋯Cl) and the CC π electron system (O–H⋯π). DFT calculations suggest that MeOH approaches CMP in five different orientations. The structural, energetic, and spectroscopic parameters of the most stable structures in each orientation were studied, and their binding energies range from −25.5 to −19.5 kJ mol−1. The docking to the π system is at least 1 kJ mol−1 more favored than the docking to the chlorine atom. The equilibrium constant for complexation (2.3 × 10−2) was determined from the experimental and calculated intensity of the OH-stretching transition. The Gibbs free energy of formation was found to be 9.3 kJ mol−1. The nature of the non-covalent interaction was analyzed with the atoms in molecules (AIM) method.

Matrix isolation study of the early intermediates in the ozonolysis of selected vinyl ethers

The matrix isolation technique combined with infrared spectroscopy has been used to characterize Criegee Intermediates (CI) and other products formed during the ozonolysis reactions of ethyl vinyl ether and n-butyl vinyl ether. Twin jet deposition at 14 K led to a number of new bands indicating the formation of products, with an intensity increase of ∼150% to 400% when annealing to 30 K. All the infrared absorptions could be assigned to different bands, which provided direct evidence for the formation of primary ozonides, CI and secondary ozonides in the systems investigated. Theoretical calculations at the B3LYP-D3/aug-cc-pVTZ level were carried out to complement the experimental observations. Experimental and theoretical results demonstrate that the studied ozonolysis reactions predominantly follow the Criegee mechanism. The current results will allow a better assessment of the potential environmental impacts of vinyl ethers.