- The Ozonolysis of Ethylene. Microwave Spectrum, Molecular Structure, and Dipole Moment of Ethylene Primary Ozonide (1,2,3-Trioxolane)
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The gas-phase structure of ethylene primary ozonide (CH2CH2OOO) has been determined from millimeter wave spectra of five isotopic species.Partial substitution, rs, parameters for the lowest energy oxygen envelope conformation (Cs symmetry) are r(CC) = 1.546(3) angstroem, r(CO) = 1.417(10) angstroem, r(OO) = 1.453(10) angstroem, r(CHendo) = 1.088(5) angstroem, r(CHexo) = 1.095(5) angstroem, θ(CCO) = 103.9(2) deg, θ(COO) = 102.1(4) deg, θ(OOO) = 100.1(12) deg, and θ(HCH) = 111.6(3) deg.The electric dipole moment of the normal isotopic species is 3.43(4) D.Two vibrational states, 98(6) and 171(18) cm-1 above the ground state, have been assigned to successive excitations of the pseudorotational mode which corresponds to a ring-twisting vibration of the five-membered ring.The barrier to pseudorotation is estimated to be high (greater than 300 to 400 cm-1) in agreement with ab inito MO calculations.Ethylene primary ozonide, dioxirane (CH2OO), formaldehyde, and ethylene secondary ozonide (CH2OCH2OO) are observed as products of the ozone-ethylene reaction in the low-temperature microwave cell. A mechanism of the ozonolysis of ethylene is presented which suggests that the reaction occurs primarily in the condensed phase on the surface of the cell.Microwave techniques utilizing cis- and trans-CHD=CHD show that ozone adds stereospecifically to ethylene in the formation of ethylene primary ozonide.
- Gillies, J. Z.,Gillies, C. W.,Suenram, R. D.,Lovas, F. J.
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- Environmental effects on the formation of the primary and secondary ozonides of ethylene at cryogenic temperatures
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Ethylene and ozone were co-deposited in a cryogenic matrix of argon at 15-26 K and of CO2 at 12-20 K. In the argon matrix, no perceptible reaction took place at any temperature below the softening onset of the matrix, while formation of ethylene ozonides (both primary and secondary) was observed at temperatures as low as 25 K in the amorphous CO2 matrix. The ozonides were identified by their infrared spectra, whose assignments were confirmed with the help of an ab initio calculation. The same reaction is imperceptible in a crystalline CO2 matrix deposited at 65 K, becoming observable only at 77 K and higher temperatures. Molecular dynamics simulations carried out for the solid argon host indicate that a highly organized crystalline structure does not allow the motions required for the reactions. These restrictions are apparently less stringent in the amorphous solid CO2, suggesting it as a suitable solvent for the study of reactions having a low activation barrier.
- Samuni,Fraenkel,Haas,Fajgar,Pola
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- Matrix effects in the low-temperature ozonation of ethylene, tetramethylethylene and 1-hexene
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The ozonation of the title compounds was studied in argon and CO2 matrices at low temperatures (12-80 K). All three were found to react with ozone in a CO2 matrix deposited at low temperature, and having an amorphous structure. The reaction was found to start at 26 K, the temperature at which the matrix undergoes a phase transition. In contrast, only tetramethylethylene (TME) was found to react in an argon matrix, the other two compounds remaining inactive towards ozone up to the softening temperature of argon (~40 K). These results are interpreted as indicating that reaction between olefins and ozone is initiated at low temperatures once the two reactants are free to move to the required configuration. This idea is supported by molecular dynamics simulations on the TME reaction. The infrared spectra of the primary ozonide of TME, as well as of the primary and secondary ozonide of 1-hexene are reported, and compared with quantum chemical calculations.
- Samuni,Haas,Fajgar,Pola
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- Reactions of alkenes with ozone in the gas phase: A matrix-isolation study of secondary ozonides and carbonyl-containing reaction products
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Gas phase ozonolysis reactions of the alkenes ethene, cis- and trans-but-2-ene, isoprene and the monoterpenes α-pinene, β-pinene, 3-carene, limonene and β-myrcene have been carried out and the reaction products have been trapped in O2-doped-argon matrices onto a CsI window held at 12 K. Products have been identified by IR spectroscopy. Comparison with previous matrix spectra, where secondary ozonides have been generated either in situ by annealing or in solution reactions allows a positive identification of the secondary ozonides of ethene and of cis and trans-but-2-ene to be made. These observations are backed up by experiments utilizing the isotopes 13C and 2H (D). It appears that secondary ozonides have also been formed from isoprene and the range of monoterpenes studied; this hypothesis is based upon the similarity of spectral features seen in the products of these reactions within those of the simpler alkenes. A number of other primary and secondary products are also identified from these reactions. Ethene gives formaldehyde as a primary product and acetaldehyde as a secondary product; it is found that the yield of acetaldehyde compared to formaldehyde increases as the reaction times are increased. Formaldehyde, one of the expected primary products, is formed by ozonolysis of β-pinene, although the other expected primary product, nopinone, is not seen. A range of secondary reaction products have been identified from the ozonolysis of the monoterpenes studied.
- Feltham, Emma J.,Almond, Matthew J.,Marston, George,Ly, Vivienne P.,Wiltshire, Karen S.
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p. 2605 - 2616
(2007/10/03)
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- Formation of secondary ozonides in the gas phase low-temperature ozonation of primary and secondary alkenes
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The gas-phase ozonation of a series of alkenes RCH=CH2 (R = Et, Hex), trans-RHC=CHR (R = Me, Et, Pri) and Me2C=CMe2 at -40 to 20°C, and that of ethene H2C=CH2 at -120 to 0°C at 10-4 v/v concentrations in N2 at atmospheric pressure have been studied. Using complementary product analysis by means of GC-FTIR and GC-MS techniques, we present conclusive evidence for the formation of secondary alkene ozonides as high-yield products in all instances except Me2C=CMe2. It is shown that the stereoselectivity for the conversion of trans-RHC=CHR (R = Me, Et, Pri) to trans-secondary ozonides in the gas phase is similar to that observed earlier in solution, and that the yields of secondary ozonides from RHC=CH2, but not those from RHC=CHR, significantly decrease with increasing temperature.
- Fajgar, Radek,Vitek, Josef,Haas, Yehuda,Pola, Josef
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p. 239 - 248
(2007/10/03)
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- Crossed Ozonide Formation in the Ozonolysis of Styrene
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Styrene-benzaldehyde mixtures (unsubstituted and the p-nitro, p-chloro, and p-methyl systems) were ozonized in CDCl3 at 0 deg C.The yields of styrene ozonide and of the two crossed ozonides (stilbene and ethylene ozonides) were determined.The cleavage dir
- Painter, M. Kimberly,Choi, Hyung-Soo,Hillig, Kurt W.,Kuczowski, Robert L.
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p. 1025 - 1028
(2007/10/02)
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- MECHANISM OF THE OZONOLYSIS OF PROPENE IN THE LIQUID PHASE.
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Propylene was ozonized in isobutane, hlorodifluoromethane, and methyl chloride solvents. Propylene ozonide, ethylene ozonide, and 2-butene ozonide (cis and trans isomers) were obtained in ratios of about 82:16:2. The amount of butene ozonide increased while that of ethylene ozonide usually decreased for reactions in the presence of added acetaldehyde. The cis-trans stereochemistry of the butene cross ozonide from propylene was studied at various conditions. Usually the cis isomer was preferentially formed, but addition of acetaldehyde could alter this. The cis-(trans-butene ozonide ratio was 67/33 when formed from cis- or trans-2-butene in CHClF//2 and 50/50 as a cross ozonide from trans-2-pentene. The kinetic secondary isotope effects upon ozonolysis of propene-2-d//1 (k//H/k//D equals 0. 88 (6) and propene-1-d//1 (0. 88 (8) were evaluated. These results are discussed with reference to the Criege mechanism of ozonolysis. 37 refs.
- Choe,Srinivasan,Kuczkowski
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p. 4703 - 4704
(2007/10/02)
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- Infrared Spectrum of the Primary Ozonide of Ethylene in Solid Xenon
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Separate Xe/O3 and Xe/C2H4 mixtures were condensed on a CsI window at 50 K and then warmed to 80-100 K.Strong infrared absorption due to the secondary ozonide and weaker bands at 409, 647, 727, 846, 927, 983, and 1214 cm-1 replaced the ethylene and ozone absorptions.The latter new bands agree with earlier solid film and CO2 matrix studies and are assigned to the primary ozonide.Isotopic substitution (16,18O3, 18O3, CH2CD2, C2D4, 13C2H4) provides a sound basis for vibrational assignments.A sextet splitting for the 647-cm-1 antisymmetric O-O-O stretching mode in the 50percent oxygen-18 enriched experiment confirms the primary ozonide structure and directly characterizes the weak O-O-O single bonds.
- Kohlmiller, Christopher K.,Andrews, Lester
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p. 2578 - 2583
(2007/10/02)
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- A FT IR Study of a Transitory Product in the Gas-Phase Ozone-Ethylene Reaction
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Further kinetic and spectroscopic characterization was made with the FT IR method for the transistory species (compound X) detected originally by Heath et al. and more recently Su et al. in the gas-phase reaction between O3 and C2H4.The results obtained support the earlier suggestion of Su et al. that compound X is HOCH2OCHO formed by the secondary reaction of the thermally stabilized CH2OO entity with CH2O.
- Niki, H.,Maker, P. D.,Savage, C. M.,Breitenbach, L. P.
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p. 1024 - 1027
(2007/10/02)
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- The Mechanism of Ozone-Alkene Reactions in the Gas Phase. A Mass Spectrometric Study of the Reactions of Eight Linear and Branched-Chain Alkenes
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The stable products of the low-pressure (4 - 8 torr (1 torr = 133.33 Pa)) gas-phase reactions of ozone with ethene, propene, 2-methylpropene, cis-2-butene, trans-2-butene, trans-2-pentene, 2,3-dimethyl-2-butene, and 2-ethyl-1-butene have been identified by using a photoionization mass spectrometer coupled to a stirred-flow reactor.The products observed are characteristic of (i) a primary Criegee split to an oxoalkane (aldehyde or ketone) and a Criegee intermediate, (ii) reactions of the Criegee intermediates such as unimolecular decomposition, secondary ozonide formation, etc., and (iii) secondary alkene chemistry involving OH and other free-radical products formed by the unimolecular decomposition of the Criegee intermediates.The secondary OH - alkene - O2 reactions account for a significant fraction of the alkene (CnH2n) consumed and lead to characteristic products such as Cn dioxoalkanes nH2n + 30)>, Cn acyloins nH2n + 32)>, and Cn alkanediols nH2n + 34)>.Cn oxoalkanes and Cn epoxyalkanes observed at m/e (CnH2n + 16) are probably formed primarily via epoxidation of the alkene by O3.A general mechanism has been proposed to account for the observations.
- Martinez, Richard I.,Herron, John T.,Huie, Robert E.
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p. 3807 - 3820
(2007/10/02)
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