Fourier transform ion cyclotron resonance detection of multiphoton ionization spectroscopy

1997

J. Am. Chem. Soc.

The formation of C6SiH7 + from phenylsilane was studied using Fourier transform ion cyclotron resonance spectrometry and by ab initio calculations. The (parent − H or D)+ ions were produced by electron impact (EI) dissociation of C6H5SiH3 and C6H5SiD3, and their bimolecular reactivities toward phenylsilane, cycloheptatriene, benzyl chloride, benzene-d 6, and toluene-d 8 were examined. The reactive component that abstracts hydride from phenylsilane and cycloheptatriene or chloride from benzyl chloride is mostly the phenylsilyl cation C6H5SiH2 +. The identity of the unreactive component was characterized by collision-induced dissociation and bimolecular chemical reactivity. The low-energy collision-induced dissociation of the unreactive C6SiH7 + ion with argon yielded SiH+ with a loss of C6H6 and C6SiH5 + with a loss of H2 as the primary fragments. Vibrationally hot C6SiH7 + ions from EI of C6H5SiH3 reacted with benzene-d 6 to form C6D6·SiH+ adducts, which after few seconds of cooling delay remained unreactive toward cycloheptatriene. Ab initio calculations predict the hydride affinity of C6H6·SiH+ that forms C6H6 + SiH2 to be comparable to or lower than that of tropylium ion. The chloride affinity of C6H6·SiH+ that forms C6H6 + SiHCl is estimated to be ∼4 kcal mol-1 lower than that of the benzyl cation. Both experiment and theory suggest the C6H6·SiH+ adduct as the unreactive C6SiH7 + component and not the silacycloheptatrienyl cation. The mechanism of the formation of C6H6·SiH+ is presented based on the theoretical energetics of radical cations and the transition state for the [1,2] sigmatropic migration of an α-H.

Section: Methodsmentioning

confidence: 99%

Experimental and Theoretical Studies of Silacycloheptatrienyl Cation Formation from Phenylsilane

1997

J. Am. Chem. Soc.

“…36,56 Experimental procedures pertinent to the present study are outlined below. The FT-ICR spectrometer used in this study consisted of a 1.0-T electromagnet ͑Varian͒, a vacuum chamber with a homebuilt 1.85-in.…”

Section: Methodsmentioning

confidence: 99%

Solvation of the Li+–Cl−–Li+ triple ion in the gas phase

Denson

The Journal of Chemical Physics

1998

Articles you may be interested inThe effects of charge transfer on the aqueous solvation of ions J. Chem. Phys. 137, 044511 (2012); 10.1063/1.4736851 Modeling the hydration of mono-atomic anions from the gas phase to the bulk phase: The case of the halide ions F−, Cl−, and Br− J. Chem. Phys. 136, 044509 (2012); 10.1063/1.3678294Computation of methodology-independent single-ion solvation properties from molecular simulations. III. Correction terms for the solvation free energies, enthalpies, entropies, heat capacities, volumes, compressibilities, and expansivities of solvated ions Fourier-transform ion cyclotron resonance ͑FT-ICR͒ spectrometry was employed to study solvations of the Li ϩ -Cl Ϫ -Li ϩ triple ion with oxygen-donor Lewis bases in the gas phase. The LiClLi ϩ triple ions were produced in an ICR cell by laser desorption ionization of a lithium chloride/ dibenzo-18-crown-6-ether matrix pasted on a Teflon substrate. O-donor Lewis bases include 1,4-dioxane, 1,3-dioxane, tetrahydrofuran ͑THF͒, acetone and diethyl ether. All O-donors associate directly with LiClLi ϩ with the maximum solvation numbers of 3 for 1,4-dioxane, 1,3-dioxane and diethyl ether, and 4 for THF and acetone at room temperature. The rate constants for the stepwise solvations were measured, and the solvent binding energies were determined from van't Hoff plots. The structures and energetics of LiClLi ϩ and the 1:1 complexes of Li ϩ and LiClLi ϩ with the dioxanes, THF, and acetone were calculated at the Hartree-Fock ͑HF͒ level with a 6-311G(d,p) basis set, and those of more highly coordinated LiClLi ϩ complexes were calculated with a 6-31G(d) basis set. Solvation enthalpies and free energies were calculated, and solvent binding energies were compared with experiments. The mechanisms of stepwise solvations of the LiClLi ϩ triple ion with dioxanes, THF, and acetone are discussed in light of experimental kinetics and binding energies and theoretical structures and solvation energies.

“…Experimental setups were previously described in detail. , Experimental procedures pertinent to the present study are outlined below. The FT-ICR spectrometer used in this study consisted of a 1.2 T electromagnet (Varian), a vacuum chamber with a homebuilt 1.85-in.…”

Section: Methodsmentioning

confidence: 99%

Solvation of the Li⁺−Br^-−Li⁺ Triple Ion in the Gas Phase

1997

J. Am. Chem. Soc.

The solvation of the Li+−Br-−Li+ triple ion with oxygen-donor Lewis bases was studied in the gas phase with use of Fourier-transform ion cyclotron resonance spectrometry. The Li+−Br-−Li+ triple ions were prepared in an ICR cell by matrix-assisted laser desorption ionization of a lithium bromide/dibenzo-18-crown-6-ether matrix pasted on a Teflon substrate. The stepwise solvations of LiBrLi+ were examined with oxygen-containing Lewis bases: 15-crown-5-ether (15C5), 12-crown-4-ether (12C4), 1,4-dioxane, 1,3-dioxane, and tetrahydrofuran (THF). Crown ethers solvate Li+ with loss of LiBr. 15-Crown-5-ether yields a 1:1 (15C5)·Li+ complex as the end product, whereas 12-crown-4-ether forms a 2:1 (12C4)2·Li+ complex. On the other hand, low dielectric constant solvents, such as dioxanes and THF, solvate the Li+−Br-−Li+ triple ion rather than abstracting Li+ with loss of the neutral ion pair. The maximum coordination numbers are 3 for dioxanes and 4 for THF at 293 K. The rate constants for the stepwise solvations were measured, and the binding energies were determined from the temperature dependence of the equilibrium constants. The mechanisms of stepwise solvations are discussed in light of the structures and energetics of the 1:1 complexes of Li+ and LiBrLi+ with dioxanes and THF calculated at the Hartree−Fock level with a standard 6-311G(d,p) basis set.