Why CH3CH3+* formation competes with H* loss from CCCO C3H6O+* isomers

How formation of CH3CH3+* competes with H* loss from C3H6O+* isomers with the CCCO framework has been a puzzle of gas phase ion chemistry because the first reaction has a substantially higher threshold and a supposedly tighter transition state. These together should make CH3CH3+* formation much the slower of the two reactions at all internal energies. However, the rates of the two reactions become comparable at about 20 kJ x mol(-1) above the threshold for CH3CH3+* formation. It was recently shown that losses of atomic fragments increase in rate much more slowly with increasing internal energy than do the rates of competing dissociations to two polyatomic fragments. This occurs because fewer frequencies are substantially lowered in transition states for the former type of reaction than for the latter. The resulting lower transition state sums of states cause the rates of dissociations producing atoms as fragments to increase much more slowly than competing processes with increasing energy. Here we show that this is why CH3CH3+* formation competes with H* loss from CH3CH2CHO+*. These results further establish that the dependence on energy of the rate of a simple unimolecular dissociation is usually directly related to the number of rotational degrees of freedom in the products, a newly recognized factor in determining the dependence of unimolecular reaction rates on internal energy.     

Collisions of slow polyatomic ions with surfaces: dissociation and chemical reactions of C2H2+*, C2H3+, C2H4+*, C2H5+, and their deuterated variants C2D2+* and C2D4+* on room-temperature and heated carbon surfaces

Interaction of C2Hn+ (n = 2-5) hydrocarbon ions and some of their isotopic variants with room-temperature and heated (600 degrees C) highly oriented pyrolytic graphite (HOPG) surfaces was investigated over the range of incident energies 11-46 eV and an incident angle of 60 degrees with respect to the surface normal. The work is an extension of our earlier research on surface interactions of CHn+ (n = 3-5) ions. Mass spectra, translational energy distributions, and angular distributions of product ions were measured. Collisions with the HOPG surface heated to 600 degrees C showed only partial or substantial dissociation of the projectile ions; translational energy distributions of the product ions peaked at about 50% of the incident energy. Interactions with the HOPG surface at room temperature showed both surface-induced dissociation of the projectiles and, in the case of radical cation projectiles C2H2+* and C2H4+*, chemical reactions with the hydrocarbons on the surface. These reactions were (i) H-atom transfer to the projectile, formation of protonated projectiles, and their subsequent fragmentation and (ii) formation of a carbon chain build-up product in reactions of the projectile ion with a terminal CH3-group of the surface hydrocarbons and subsequent fragmentation of the product ion to C3H3+. The product ions were formed in inelastic collisions in which the translational energy of the surface-excited projectile peaked at about 32% of the incident energy. Angular distributions of reaction products showed peaking at subspecular angles close to 68 degrees (heated surfaces) and 72 degrees (room-temperature surfaces). The absolute survival probability at the incident angle of 60 degrees was about 0.1% for C2H2+*, close to 1% for C2H4+* and C2H5+, and about 3-6% for C2H3+.     

G3(MP2) study of the C3H6O+* isomers fragmented from 1,4-dioxane+*

The fragmentation process of ionized 1,4-dioxane and the reactions between the C3H6O+* ions, one of the major fragments, and various reactants (including acetonitrile, formaldehyde, ethylene, and propene) have been studied experimentally with mass spectrometry. In the present work, G3(MP2) calculations were carried out to investigate these processes theoretically. In agreement with experiment, isomers CH3OCHCH2+* (1) and *CH2CH2OCH2+ (2) were found to be the C3H6O+* ions fragmented from ionized 1,4-dioxane, with 2 being the major product. The mechanisms of the formation of 1 and 2 were successfully established. In addition, the characteristic reactivities, as well as the corresponding reaction mechanisms, of both isomers were rationalized with the aid of calculations. Finally, a minor reaction between isomer 2 and propene was identified, and the presence of the product of this reaction was found to be useful in explaining the aforementioned mass spectrometric data.     

Multiple photon induced chemistry in mixtures of C2F6 with H2 or C6H14

CO₂ laser induced chemistry is demonstrated to occur efficiently in mixtures of C₂F₆ with H₂ or C₆H₁₄ at a fluence of 6 J/cm² and for a 30 cm^-1 red-shift from the C₂F₆ absorption maximum. H₂ or C₆H₁₄ pressure may be used to control the distribution of product species.     

Structural and photophysical studies of phenanthrene adducts involving C6F5HgCl and [o-C6F4Hg]3

Both pentafluorophenylmercury chloride and trimeric perfluoro-ortho-phenylene mercury interact with phenanthrene to form phosphorescent adducts which exhibit extended binary stacks in the solid state.     

Multidentate aryloxide and oxo-aryloxide complexes of antimony: synthesis and structural characterization of [eta4-N(o-C6H4O)3]Sb(OSMe2), {{[eta3-N(o-C6H4OH)- (o-C6H4O)2]Sb}2(mu2-O)}2 and {[eta3-PhN(o-C6H4O)2]Sb}4(mu3-O)2

Antimony compounds that feature multidentate aryloxide ligands, namely [eta4-N(o-C6H4O)3]Sb(OSMe2), {{[eta3-N(o-C6H4OH)(o-C6H4O)2]Sb}2(mu2-O)}2, and {[eta3-PhN(o-C6H4O)2]Sb}4(mu3-O)2 have been synthesized from N(o-C6H4OH)3 and PhN(o-C6H4OH)2 and structurally characterized by X-ray diffraction. While [eta4-N(o-C6H4O)3]Sb(OSMe2) exists as a discrete mononuclear species, the oxo complexes {{[eta3-N(o-C6H4OH)(o-C6H4O)2]Sb}2(mu2-O)}2 and {[eta3-PhN(o-C6H4O)2]Sb}4(micro3-O)2 are multinuclear. Specifically, the dinuclear fragment {[eta3-N(o-C6H4OH)(o-C6H4O)2]Sb}2(mu2-O)} exists in a dimeric form due to the bridging oxo ligand participating in an intermolecular hydrogen bonding interaction, while the dinuclear fragment {[eta3-PhN(o-C6H4O)2]Sb}2(mu-O) exists in a dimeric form due to the bridging oxo ligand serving as a donor to the antimony of a second fragment. The structures of {{[eta3-N(o-C6H4OH)(o-C6H4O)2]Sb}2(mu2-O)}2 and {[eta3-PhN(o-C6H4O)2]Sb}4(mu3-O)(2), therefore, indicate that an oxo ligand bridging two Sb(III) centers is sufficiently electron rich to serve as both an effective hydrogen bond acceptor and as a ligand for an additional Sb(III) center.     

Neue Synthesen und Kristallstrukturen von Bis(fluorphenyl)quecksilber,Hg(Rf)2 (Rf = C6F5, 2, 3, 4, 6‐F4C6H, 2, 3, 5, 6‐F4C6H, 2, 4, 6‐F3C6H2, 2, 6‐F2C6H3)

New Syntheses and Crystal Structures of Bis(fluorophenyl) Mercury, Hg(R_f)₂ (R_f = C₆F₅, 2, 3, 4, 6‐F₄C₆H, 2, 3, 5, 6‐F₄C₆H, 2, 4, 6‐F₃C₆H₂, 2, 6‐F₂C₆H₃) Bis(fluorophenyl) mercury compounds, Hg(R_f)₂ (R_f = C₆F₅, C₆HF₄, C₆H₂F₃, C₆H₃F₂), are prepared in good yields by the reactions of HgF₂ with Me₃SiR_f. The crystal structures of Hg(2, 3, 4, 6‐F₄C₆H)₂ (monoclinic, P2₁/n), Hg(2, 3, 5, 6‐F₄C₆H)₂ (monoclinic, C2/m), Hg(2, 4, 6‐F₃C₆H₂)₂ (monoclinic, P2₁/c) and Hg(2, 6‐F₂C₆H₃)₂ (triclinic, P1) are described.     

Kinetics of Depletion of Electronically Excited Ti Atom by CH4, C2H2, C2H4 and C2H6

The kinetics of depletion of ground state Ti(a³F) and electronically excited state Ti(a⁵F) upon interactions with CH₄, C₂H₂, C₂H₄, and C₂H₆ are studied in a fast-flow reactor at a He pressure of 0.70 Torr. No depletion of ground state Ti(a³F) was observed upon interaction with all hydrocarbons studied here. Two alkanes, CH₄ and C₂H₆, were also quite inert for depletion of the excited state Ti(a⁵F), On the other hand, C₂H₂ and C₂H₄ deplete the excited state Ti(a⁵F) very efficiently. Rate constants were determined to be (266 ± 86) and (476 ± 88) × 10^?12 cm³s^?1 for Ti(a⁵F) + C₂H₄ and Ti(a⁵F) + C₂H₂, respectively. These large rate constants compared with the ground state Ti were explained by an electron donor-acceptor interaction model that works in the interaction between C₂H₄ or C₂H₂ and the excited state with unfilled 4s orbital.     

An ab-initio study of the C3H6-HX, C2H4-HX and C2H2-HX hydrogen-bonded complexes with X=F or Cl.

MP2/6-31G** ab-initio molecular orbital calculations have been performed to obtain geometries, H-bond energies and vibrational properties of the C3H6-HX, C2H4-HX and C2H2-HX H-bonded complexes with X=F or Cl. The more pronounced effects on the structural parameters of the isolated molecules due to complexation are verified to the CC and HX bond lengths, which are directly involved in the H-bond formation. They are increased after complexation. The calculated H-bond lengths for the hydrogen complexes for X=F are shorter than those for x-Cl by about 0.55 A, whereas the corresponding experimental value is 0.58 A. The H-bond energies are essentially determined by the nature of the proton donor molecule. For X=F, the AE mean value is 20 kJ/mol, whereas it is approximately 14.5 kJ/mol for X-Cl. The H-bond energies including zero-point corrections show a good correlation with the H-bond lengths. The more pronounced effect on the normal modes of the isolated molecules after complexation occurs to the H-X stretching mode. The H-X stretching frequency is shifted downward, whereas its IR intensity is much enhanced upon H-bond formation. The new vibrational modes arising from complexation show several interesting features.     

Simultaneous thermoanalytical investigations of (C6H5)4AsCl and (C6H5)4PCl under air and argon atmospheres

The thermoanalytical curves of (C₆H₅)₄AsCl (I) and (C₆H₅)₄PCl (II) were generated simultaneously by using a Netzsch simultaneous thermal analyser 409 under static air and dynamic argon atmospheres. The ranges of thermal stability of I and II were found to be 145–310°C and 137–365°C, respectively, and their melting points to be 261 and 278°C. The DTA profiles of I and II differ and can be used for their distinction.     

Total cross sections for electron scattering by polyatomic molecules at 10–1000 eV: C2H2, C2H4, C2H6, C3H6, C3H8 and C4H8

A model complex optical potential (composed of static, exchange, polarization and absorption terms) is employed to calculate the total (elastic and inelastic) electron-atom scattering cross sections from the corresponding atomic wave function at the Hartree-Fock level. The total cross sections (TCS) for electron scattering by their corresponding molecules (C₂H₂, C₂H₄, C₂H₆, C₃H₆, C₃H₈ and C₄H₈) are firstly obtained by the use of the additivity rule over an incident energy range of 10–1000 eV. The qualitative molecular results are compared with experimental data and other calculations wherever available, good agreement is obtained in intermediate-and high-energy region.     

Activation of H2 by phosphinoboranes R2PB(C6F5)2

Phosphinoboranes that combine bulky electron-rich phosphides and electron deficient B(C6F5)2 fragments produce monomeric phosphinoboranes that undergo facile addition of H2 to give the phosphine-borane adducts (R2PH)(HBR'2). This finding in combination with DFT calculations shed light on the uptake of H2 across a group 13-group 15 bond, a critical requirement for the development of recyclable H2 storage materials.     

Syntheses and Characterizations of (4-NH2C6H4S)4Sn and [(4-NH2C6H4S)2(4-NH3C6H4S)2Sn]Cl2

1INTRODUCTIONInrecentyears,theresearchesontinsulfidemateri-alshavedrawnchemists’attentionowningtotheirpo-tentialapplicationsasphotovoltaicmaterials,hologra-phicrecordingsystem[1,,solarcontroldevices[3]and2]semiconductormaterials.Ageneralmethodtopreparetinsulfidesisthechemicalvapourdepositionfromdi-scretesimpletin-sulfidecomplexes,suchas(PhS)4Sn,Sn(SCy)4and[CF3(CF2)5S]4Sn[4].Duringoureffortinsynthesizingtin-sulphurcomplexes[5],weobtainedtwomononucleartincomplexes,(4-NH2C6H4S)4Sn1an…     

GF Calculations for some tricyclic molecules: C3H6, C3H4, C2H4NH,C2H4O and C2H4S

We have functions expressed as antisymmetrized products of strongly orthogonal geminals have been evaluated for some three membered ring molecules. GF results are compared with previously computed SCF-MO results, obtained employing the same atomic basis. Transferability features of bonds and inner shells are shown.