Computational Study of the Dissociation Reactions of Secondary Ozonide

This contribution presents a comprehensive computational study on the reactions of secondary ozonide (SOZ) with ammonia and water molecules. The mechanisms were studied in both a vacuum and the aqueous medium. All the molecular geometries were optimized using the B3LYP functional in conjunction with several basis sets. M06-2X, APFD, and ωB97XD functionals with the full basis set were also used. In addition, single-point energy calculations were performed with the G4MP2 and G3MP2 methods. Five different mechanistic pathways were studied for the reaction of SOZ with ammonia and water molecules. The most plausible mechanism for the reaction of SOZ with ammonia yields HC(O)OH, NH3, and HCHO as products, with ammonia herein acting as a mediator. This pathway is exothermic and exergonic, with an overall barrier height of only 157 kJ mol−1 using the G3MP2 method. All the reaction pathways between SOZ and water molecules are endothermic and endergonic reactions. The most likely reaction pathway for the reaction of SOZ with water involves a water dimer, in which the second water molecule acts as a mediator, with an overall barrier height of only 135 kJ mol−1 using the G3MP2 method. Solvent effects were found to incur a significant reduction in activation energies. When the second H2O molecule acts as a mediator in the reaction of SOZ with water, the barrier height of the rate-determining step state decreases significantly.

The influences of ammonia on aerosol formation in the ozonolysis of styrene: roles of Criegee intermediate reactions

The influences of ammonia (NH 3 ) on secondary organic aerosol (SOA) formation from ozonolysis of styrene have been investigated using chamber experiments and quantum chemical calculations. With the value of [O 3 ] 0 /[styrene] 0 ratios between 2 and 4, chamber experiments were carried out without NH 3 or under different [NH 3 ]/[styrene] 0 ratios. The chamber experiments reveal that the addition of NH 3 led to significant decrease of SOA yield. The overall SOA yield decreased with the [NH 3 ] 0 /[styrene] 0 increasing. In addition, the addition of NH 3 at the beginning of the reaction or several hours after the reaction occurs had obviously different influence on the yield of SOA. Gas phase reactions of Criegee intermediates (CIs) with aldehydes and NH 3 were studied in detail by theoretical methods to probe into the mechanisms behind these phenomena. The calculated results showed that 3,5-diphenyl-1,2,4-trioxolane, a secondary ozonide formed through the reactions of C 6 H 5 ĊHOO· with C 6 H 5 CHO, could make important contribution to the aerosol composition. The addition of excess NH 3 may compete with aldehydes, decreasing the secondary ozonide yield to some extent and thus affect the SOA formation.

Direct kinetics study of CH2OO + methyl vinyl ketone and CH2OO + methacrolein reactions and an upper limit determination for CH2OO + CO reaction

Reactions of Criegee intermediate CH2OO with unsaturated carbonyl compounds form secondary ozonide products.

Conformational isomerism of 1-butene secondary ozonide as studied by means of matrix isolation infrared absorption spectroscopy

Theoretical calculations of structures, stability and vibrational spectra of 1-butene secondary ozonide (SOZ) conformers were performed using DFT method B3LYP with a 6-311++G(3df, 3pd) basis set. The calculations predict six staggered structures of 1-butene SOZ. The FTIR spectra of 1-butene SOZ isolated in Ar, N2 and Xe matrices were recorded. It was found that nitrogen is the best suited for the matrix isolation of 1-butene SOZ. The bandwidth of the spectral bands of the ozonide isolated in nitrogen was as narrow as 2 cm−1. For the first time the existence of five conformers of 1-butene SOZ were confirmed experimentally by means of matrix isolation infrared absorption spectroscopy. The equatorial gauche (∠OCCC=−66.1°) conformer was proved theoretically and experimentally to be the most stable. It was found that due to high potential barriers of the conformational transitions annealing of the matrix is useless for the assignment of spectral bands to various conformers of 1-butene SOZ. Using the hot nozzle technique the van’t Hoff experimental plots were made for three additional conformers of 1-butene SOZ and experimental ΔH values for these additional conformers were established. The crystallization problems of 1-butene SOZ are discussed which accounts for the rich conformational diversity of the ozonide as well as high conformational barriers for axial-equatorial transitions.

Synthesis and X-Ray Crystal Structure Analysis of 1,4-Epoxy-4-methyl- 1H,4H-2,3-benzodioxepin

Ozonolysis of 2-methyl-1H-indene (1) afforded the stable secondary ozonide 1,4-epoxy-4-methyl- 1H,4H-2,3-benzodioxepin (2). This compound crystallizes in two polymorphic forms, depending on the solvent used. The monoclinic form 2a containing two symmetry-independent molecules (enantiomers) is obtained by crystallization from dichloromethane. In contrast, the orthorhombic modification 2b is obtained from ethyl acetate solution and crystallizes as a conglomerate of enantiomerically pure single crystals. Additionally, the ring-opened product 2-(2-oxopropyl)benzoic acid (3) was obtained and investigated by X-ray crystal structure analysis.

Matrix isolation FTIR spectroscopical study of ethene secondary ozonide

A new method is used for the separation of ethene secondary ozonide (SOZ) from the other products of ethene ozonization reaction. The reaction was performed in the neat films of the reactants at 77 K. Ethene SOZ was separated from other products of the reaction by vacuum distillation at 190–210 K and analyzed by means of the matrix isolation IR absorption spectroscopy. Spectroscopic data from photolysis of the matrix isolated ozonide was used as an argument for assignment of the infrared spectral bands either to ethene SOZ or to other products of the reaction. The spectra of ethene SOZ isolated in the Ar matrix were analyzed by combining experimental results with the theoretical calculations performed at the MP2 6-311+G (3df, 3pd) level. A new assignment of some experimental fundamental bands is proposed taking in to account the Fermi resonance between CH stretch and the five membered ring vibrations. For the first time more than 30 weak infrared absorption bands were observed and assigned to various combination vibrations and overtones. By using new spectral information concerning the overtones and the combination bands it is concluded that the dissociation of unstable ethene SOZ involving breaking of any of the four CO bonds of the five membered ring of ethene SOZ has low probability. Dissociation of the ring starts from breaking of the OO bond.