No abstract

The reaction of ground-state oxygen atoms, 0(3P), with ethylene and ethylene-d, in liquid nitrogen solution at 77 "K has been studied. The major and perhaps the exclusive products are ethylene oxide and acetaldehyde. The ratio of acetaldehyde to ethylene oxide is 1.2 1 0.1 for ethylene and 0.91 + 0.09 for ethylene-d4. Much smaller amounts of formaldehyde and trace quantities of cyclopropane are also observed. The effect of the concentration of ethylene on the quantum yields of addition products was measured. A limiting quantum yield of oxygen atoms scavenged by ethylene to form the addition products was 0.12+0.01. The low quantum yield suggests an appreciable cage recombination of the ground-state oxygen atoms with the trace amounts of molecular oxygen present. The effect of the concentration of added oxygen on the product yields and the relative rate constant for the addition of 0(3P) to molecular oxygen and to ethylene were determined. The ratio ko+02/ko+c,H, is 6.0 i 1.0 and the relative rate constant for the addition of 0(3P) to ethylene and to ethylene-d,, ko+c,D4/ko+c,~,, is 2.0 i. 0.1. The type of products formed and the isotope effects observed are discussed in terms of the mechanism of addition of 0(3P) atoms to ethylene. La reaction des atomes d'oxygene I'Ctat fondamental, 0(3P) avec I'ethylene et ]'ethylene-d, en solution d'azote liquide a 77 "K a et6 CtudiCe. Les produits majeurs et peut-Ctre les seuls formts sont I'oxyde d'ethylene et I'adtaldLhyde. Le rapport d'acetaldehyde versus l'oxyde d'ethylene est 1.2 + 0.1 pour I'ethylene et 0.91 + 0.09 pour I'ethylene-d,. Des quantites beaucoup plus faibles de formaldehyde ainsi que des traces de cyclopropane sont aussi obtenues. L'effet de la concentration d'ethylene sur le rendement quantique des produits d'addition a Cte mesure. Un rendement quantique limite d'atomes d'oxygkne trappes par I'tthyl6ne pour former les produits d'addition a ete de 0.12 + 0.01. Le petit rendement quantique suggere une recombinaison appreciable en cage des atomes d'oxygene dans I'etat fondamental avec des quantitis minimes (traces) d'oxygene molCculaire present. L'effet de la concentration d'oxygene ajoute sur le rendement en produits et la constante de vitesse relative a I'addition de 0(3P

Publication costs assisted by the National Research Council of CanadaLow-temperature photolysis of liquid, solid, and dissolved ethylene has been studied at 184.9 nm. The major products observed in the photolysis of liquid ethylene and of ethylene-ethane solutions at -(160 * 1)" are hydrogen and acetylene. The minor products are butene-1, n-butane, 1,3-butadiene, methylcyclopropane, cyclobutane, hexene-1, and 1,5-hexadiene. Methylcyclopropane, cyclobutane, and the greater part of butene-1 appear to result from direct addition of excited ethylene molecules to ethylene. In the photolysis of dideuterioethylene in liquid nitrogen solution at 77"K, cis-trans isomerization, H-atom scrambling, molecular decomposition into hydrogen and acetylene, and a much smaller decomposition into hydrogen atoms and vinyl radicals are observed. The photolysis of liquid and dissolved ethylene may be explained by a mechanism involving either a single or, somewhat more logically, two excited states of ethylene. The two-state mechanism is formally similar to the mechanism previously postulated for the mercury (Hg(3P1)) photosensitized reaction of ethylene. Addition of vinyl radicals (but not of ethyl radicals) to ethylene at -(160 & 1)" is observed. At this temperature the ratio k(C2H3 + CzH4)/k(H + GzI14) is 0.24. Photochemically induced intermolecular hydrogen exchange at 184.9 nm between CzH4 and C2D4 in the solid phase at 77°K is at best only a very minor process. The ratio of the free radical to the molecular decomposition of liquid ethylene photolyzed at -160" is about 0.03.

The structures of the 5-oxo-2,6-diazabicyclo[2.2.0]hex-2-enes (imine Dewar pyrimidinones) 2a-h have been studied by X-ray diffraction analysis and ab initio calculations at the HF/6-31G(d,p) and MP2/6-31G(d,p) levels of theory. The crystal structures of 1-alkyl-3-tert-butyl-6-methyl imine Dewar pyrimidinones 2a-c have been determined at low temperature. The X-ray diffraction studies revealed that both the 2-azetidinone and dihydroazete rings are almost planar, and their eight bond angles are nearly 90 degrees (81-100 degrees ). The C1-N2(=C3) bond distance in the dihydroazete ring is longer due to the bond angle strain by ca. 0.06 Å than that of a typical straight-chain imine molecule. Full geometry optimizations on the imine Dewar isomers (2a and 2d-h) show deviations between the HF and MP2 geometries. The MP2 structure of the 3-tert-butyl-1,6-dimethyl imine Dewar pyrimidinone 2a is compared with those of the X-ray diffraction. The results of the calculations are found to be in good agreement with the X-ray diffraction data. The full geometry optimizations are necessary with the inclusion of electron correlation for the highly strained molecules. The ab initio calculations of the 2-azetidinone 9, 3,4-dihydroazete 11, and N-ethylidenemethylamine 12 have been carried out at the HF and MP2/6-31G(d,p) levels of theory to compare with the structures, orbital hybridization, bond orders, and charge distributions of the Dewar pyrimidinones 2. The theoretical results reveal that the MP2 C1-N2 bond distance of the Dewar pyrimidinone 2a is consistent with the abnormally elongated X-ray C1-N2 bond distance. The electronegative N2 and N6 atoms in the Dewar pyrimidinones 2 give the great positive charge on the C1 atom. The smaller bond angles (ca. 90 degrees ) in the Dewars 2 than typical sp(2) and sp(3) bond angles (ca. 120 and 109 degrees ) increase p character in the endocyclic bonds and decrease p character in the exocyclic bonds.

The reaction of ground-state oxygen atoms, 0(3P), with ethylene and ethylene-d, in liquid nitrogen solution at 77 "K has been studied. The major and perhaps the exclusive products are ethylene oxide and acetaldehyde. The ratio of acetaldehyde to ethylene oxide is 1.2 1 0.1 for ethylene and 0.91 + 0.09 for ethylene-d4. Much smaller amounts of formaldehyde and trace quantities of cyclopropane are also observed.The effect of the concentration of ethylene on the quantum yields of addition products was measured.A limiting quantum yield of oxygen atoms scavenged by ethylene to form the addition products was 0.12+0.01. The low quantum yield suggests an appreciable cage recombination of the ground-state oxygen atoms with the trace amounts of molecular oxygen present. The effect of the concentration of added oxygen on the product yields and the relative rate constant for the addition of 0(3P) to molecular oxygen and to ethylene were determined. The ratio ko+02/ko+c,H, is 6.0 i 1.0 and the relative rate constant for the addition of 0(3P) to ethylene and to ethylene-d,, ko+c,D4/ko+c,~,, is 2.0 i. 0.1.The type of products formed and the isotope effects observed are discussed in terms of the mechanism of addition of 0(3P) atoms to ethylene.