Francesco Scagnolari

Electron attachment to the fluoro‐, bromo‐, and iodomethanes studied by means of electron transmission spectroscopy and Xα calculations

The electron transmission spectra of the fluoro‐, bromo‐, and iodomethanes (except CH2F2 ) and of some monohaloalkanes are reported. The resonance energies for electron attachment to the halomethanes have also been evaluated by means of bound and continuum multiple scattering Xα calculations, which closely reproduce the low‐energy experimental data. A large electron affinity increase is observed on going from the fluorine to the heavier halogen derivatives, while within each series of halides the electron affinity increases with increasing number of halogen atoms. The ground anion state is found to be stable in CHBr3, CBr4, and in all the iodomethanes except CH3I. The fragment anion production, as a function of the electron impact energy, has been measured for some of the compounds under investigation, in order to obtain experimental information on anion states very close to zero energy or slightly stable, which are not accessible in electron transmission.

Temporary anion states in the chloromethanes and in monochloroalkanes

The resonance energies for electron attachment to the chloromethanes are evaluated by means of bound and continuum multiple scattering Xα calculations. The results closely reproduce the experimental electron transmission spectroscopy data and confirm their previous assignment. Electron transmission and dissociative attachment spectra of monochloroalkanes are also reported, in order to obtain information on the effects of branching at the substituted carbon atom and of alkyl chain length on the resonance and chlorine anion production energies.

Effect of halo-substitution on the lowest-lying empty π* orbitals in benzene derivatives: Electron transmission and dissociative attachment spectra

Abstract The electron transmission (ET) and dissociative attachment (DA) spectra of the 4-haloanisoles X-C 6 H 4 -OCH 3 (X = F, Cl, Br, I) and 4-halopyridines X-C 5 H 4 N (X = Cl, Br) are reported. The ET spectra indicate that the two lowest-lying π-anion states (deriving from the benzene 2 E 2u anion state) are almost equally stabilized by Cl, Br and I substituents. Except for fluorine, in both the anisole and pyridine derivatives the DA spectra display a peak in the fragment halogen anion yield close in energy to the lowest lying π * resonance observed in the ET spectra, regardless of its symmetry.

A reinvestigation of the mass spectra of substituted ferrocenes: accurate fragmentation pathways and ionic structures by analysis of metastable ion spectra

Abstract The mass spectra of substituted ferrocenes have been reinvestigated making intensive use of the metastable ions. The observed primary fragmentation of the molecular ions are different in some respects from those previously postulated. The study of the metastable ions characteristics of the ions at m/z 186 and m/z 121 indicates that their structures are independent of their precursor ions.

Kinetic studies in various media on some hydrogenation reactions catalyzed by polymer-anchored RhCl(PPh3)3

Abstract A study has been made of the hydrogenation of cyclohexene, 1-hexene and styrene at atmospheric pressure catalysed by RhCl (PPh 3 ) 3 supported on styrene-divinylbenzene copolymers with 1%, 2% and 4% cross linking. The dependence of the hydrogenation rate on the concentration of the olefin, the amount of catalyst, and the nature of the solvent was investigated. The hydrogenation rate is lower than for homogeneous catalysis but the dependence of the rate on the examined parameters is similar. The ratio between the rates for 1-hexene and cyclohexene is higher than that in the homogeneous phase. This increase in selectivity may due to steric hindrance around the active sites of the resin. The solvent effects revealed that the hydrogenation rate also depends on the degree of swelling of the resin.

Electronic structure of tert-butyl halides and group 14 derivatives: Electron affinities and dissociative electron attachment

Abstract Electron transmission (ET) and dissociative attachment (DA) spectroscopies are applied to the tert-butyl halides and to derivatives where the central carbon atom is replaced by a heavier group 14 element. In the tert-butyl halide series, the electron affinity increases with increasing size of the halogen atom, while in the group 14 analogues the electron affinity reaches a minimum value for the silicon derivatives. Bound-state and continuum multiple scattering Xα (MS-Xα) calculations reproduce very closely the energies of the resonances observed in the ET spectra. The DA spectra show that the ground anion state of the tert-butyl halides (except for the fluorine derivative) can decay following a dissociative channel, with halogen anion production. In the group 14 derivatives this mechanism is much less active. In some of the compounds investigated, dissociative capture of thermal electrons is also observed.

Thermodynamic features of bile salt-human serum albumin interaction

Interaction with human serum albumin is responsible for important aspects of the physiological behaviour of bile salts, although this factor has not been adequately examined. The nature of the binding is investigated here by means of thermodynamic parameters determined by equilibrium dialysis and microcalorimetric measurements. The positive enthalpy and entropy values obtained indicate the presence of a poorly specific hydrophobic bonding.

Kinetic features of olefin hydrogenations catalyzed by polymer-anchored palladium acetate

Abstract Palladium acetate anchored to polystyrylbipyridine has been used to catalyze the hydrogenations of monoalkenes at atmospheric pressure. Its kinetic behaviour and catalytic activity are independent of the metal oxidation state. The catalyst displays selectivity with respect to steric hindrance at the double bond, the hydrogenation rate decreasing on going from 1-hexene and 1-octene to cyclohexene and cyclooctene. The conversion of terminal double bonds into internal double bonds during the hydrogenations is unappreciable. Different properties and kinetic behaviour are observed after treatment of the catalyst with LiAlH 4 ; in particular, the treated catalyst induces fast isomerization reactions.

Effect of intramolecular hydrogen bonding on the empty level structure of gas-phase salicylaldehyde:electron affinities and anion yield upon electron impact

Abstract The gas-phase empty level structures of γ-butyrolactone, α-hydroxy-γ-butyrolactone, benzaldehyde, 3-hydroxybenzaldehyde and 2-hydroxybenzaldehyde (salicylaldehyde) are studied by means of electron transmission spectroscopy (ETS) and ab initio 6-31G ∗∗ calculations. The most stable conformer of salicylaldehyde is characterised by intramolecular hydrogen bonding which causes relevant geometrical variations and, in particular, a lengthening of the CO double bond. The empty π ∗ molecular orbitals of salicylaldehyde with large contribution from the carbonyl group are significantly stabilised with respect to their counterparts in benzaldehyde and in the 3-hydroxy derivative. Dissociative electron attachment spectroscopy (DAS) did not reveal formation of negative fragments at low energy, that is, the presence of dissociative decay channels for the π ∗ resonances observed in the ET spectra. The total anion current measured at the walls of the collision chamber (close to the electron beam), as a function of the incident electron energy, displays signals peaking at zero energy and at about 0.8 eV in benzaldehyde and in the two hydroxy derivatives. However, the only signal detected using a quadrupole mass filter (which requires a lifetime ≥10 −6 s) is a zero energy peak in salicylaldehyde, due to the molecular anion.

Frontier electronic structure in gas-phase epoxy and hydroxy cyclohexenes by means of photoelectron and electron transmission spectroscopies

Ionisation energy (Ei) and electron affinity (Ea) values in benzene oxide, benzene hydrate, the corresponding monoenes and other related molecules have been measured by means of UV photoelectron spectroscopy and electron transmission spectroscopy. The valence filled levels do not show evidence for strong σco–π or oxygen lone pair–π mixing in the alcohols nor in the epoxides. Although the energy perturbations, caused by the hydroxy and epoxy substituents, to adjacent filled π orbitals are small, the electron transmission spectra show that the empty π* orbitals are affected to very different extents, the epoxy substituent producing a sizeable electron affinity increase. This finding indicates the occurrence of strong interaction between the empty π* orbitals and low-energy empty σ* orbitals localised at the three-membered cycle. The experimental data have been compared with the orbital energies predicted by ab initio 3-21G calculations.