I. Orbital Interpretation and Properties of the X¹Σ⁺, a³∏, A¹∏ and ³Σ⁺ States of BH. II. Gas Phase Reactions of Fluoromethyl Cations with Ethylene and Benzene

Citation

Blint, Richard Joseph (1972) I. Orbital Interpretation and Properties of the X¹Σ⁺, a³∏, A¹∏ and ³Σ⁺ States of BH. II. Gas Phase Reactions of Fluoromethyl Cations with Ethylene and Benzene. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/KJ13-G054. https://resolver.caltech.edu/CaltechTHESIS:10282009-093808296

Abstract

"Ab initio" calculations have been carried out on the states of BH(χ¹Σ⁺, a³Π, A¹Π, and ³Σ⁺) which dissociate to the ground states of B and H. The application of the Gl method (which is a special case of the GI method) was extended to handle five- and six-electron systems, and this method along with SOGI, CI and the GVB method was used to investigate the BH states. The effect of restricting the orbitals of the wave-function to be basis functions for the irreducible representations of the spatial symmetry group leads to noncontinuous changes in the orbitals as a function of internuclear distance. And further it is noted that the removal of this restriction on the atomic wavefunction of boron leads to simple predictions of the forms of the wavefunctions, geometries of the molecules and characteristics of the potential curves for the BH_N molecules. On the basis of this the potential curves for the a³Π and A¹Π states are correctly predicted to have humps and the ²A₁ and ²B₁ states of BH₂ are predicted to be bent and linear, respectively. Molecular properties for many of these wavefunctions have been calculated and correlated with changes in the orbitals as a function of internuclear distance.

Gas phase reactions and properties of fluoromethyl cations have been investigated using the techniques of ion cyclotron resonance spectroscopy (icr). Fluoride transfer reactions between substituted methyl cations are observed to be rapid and permit the determination of relative fluoride ion affinities, defined as the negative of the enthalpy change for the reaction CH_NF⁺_3-N + F^- → CH_NF_4-N. By combining available thermochemical data and our experimental results the following order for the fluoride affinities of the methyl cations is constructed: CF⁺₃ (256.3 kcal/mole) > CH⁺₃ (252.0 kcal/mole) > CH₂F⁺ (243.6 kcal/mole) > CF₂H⁺ (242.8 kcal/mole). A measurement of the equilibrium constant for the reaction (CF₂H⁺ + CH₂F₂ ⇌ CH₂F⁺ + CF₃H) between the latter two ions has permitted their relative fluoride ion affinities to be accurately determined. Fluoride ion affinities are a means of determining carbonium ion stabilities.

With the general goal of understanding reactions involving electrophillic addition to π-systems the reactions of the fluoromethyl cations with ethylene, ethylene-d₄ and benzene-d₆ were investigated. The important process in each case involves addition of the fluoromethyl cation to the substrate to form a chemically activated intermediate which decomposes with loss of HF or H₂. Rate constants for the reactions of the fluoromethyl cations with ethylene were determined using icr trapped ion techniques. In conjunction with ion ejection double resonance, product distributions for the reactions involving ethylene-d₄ and benzene-d₆ have been determined. Only in the case of the reactions of fluoromethyl cations with benzene-d₆ is the possibility of a distinctive reaction mechanism revealed from the isotopic product distributions.

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