The β-elimination kinetics of 2,2-dihaloethyltrihalosilanes in the gas phase has been studied computationally using density functional theory (DFT) along with the M06-2x exchange–correlation functional and the aug-cc-pVTZ basis set. The calculated energy profiles have been supplemented with calculations of rate constants under atmospheric pressure and in the fall-off regime, by means of transition state theory (TST), variational transition state theory (VTST), and statistical Rice–Ramsperger–Kassel–Marcus (RRKM) theory. Activation energies and rate constants obtained using the M06-2x/aug-cc-pVTZ approaches are in good agreement with the available experimental data. Analysis of bond order, natural bond orbitals, and synchronicity parameters suggests that the β-elimination of the studied compounds can be described as concerted and slightly asynchronous. The transition states of these reactions correspond to four-membered cyclic structures. Based on the optimized ground state geometries, a natural bond orbital (NBO) analysis of donor–acceptor interactions also show that the resonance energies related to the electronic delocalization from $$\sigma_{{{\text{C}}_{ 1} {-}{\text{C}}_{ 2} }}$$
 bonding orbitals to $$\sigma^{*}_{{{\text{C}}_{ 2} - {\text{Si}}_{ 3} }}$$
 antibonding orbitals, increase from 2,2-difluoroethyltrifluorosilane to 2,2-dichloroethyltrichlorosilane and then to 2,2-dibromoethyltriboromosilane. The decrease of $$\sigma_{{{\text{C}}_{ 1} {-}{\text{C}}_{ 2} }}$$
 bonding orbitals occupancies and increase of the $$\sigma^{*}_{{{\text{C}}_{ 2} - {\text{Si}}_{ 3} }}$$
 antibonding orbitals occupancies through $$\sigma_{{{\text{C}}_{ 1} - {\text{C}}_{ 2} }} \to \sigma^{*}_{{{\text{C}}_{ 2} - {\text{Si}}_{ 3} }}$$
 delocalizations could facilitate the β-elimination of the 2,2-difluoroethyltrifluorosilane compound, compared to 2,2-dichloroethyltrichlorosilane and 2,2-dibromoethyltriboromosilane.

Theoretical study on the mechanisms and kinetics of the β-elimination of 2,2-dihaloethyltrihalosilanes (X = F, Cl, Br) compounds: a DFT study along with a natural bond orbital analysis

Infrared multiphoton absorption and dissociation of 1,2-dichloroethyltrifluorosilane molecules under the action of pulsed TEA CO2 laser were experimentally studied. The composition of dissociation products was analyzed. The only products of dissociation have been found to be stable molecules: chloroethylene and trifluorochlorosilane. Dissociation proceeds via chlorine atom transfer from carbon to silicon. The silicon isotope-selective infrared multiphoton dissociation was performed at different wavelengths of the CO2-laser radiation. High degrees of silicon isotope separation have been achieved.

Infrared multiphoton dissociation of 1,2-dichloroethyltrifluorosilane

Reaction mechanisms and kinetics of the β-elimination processes of compounds CHF2CH2SiFnMe3–n (n = 0–3): DFT and CBS-QB3 methods using Rice-Ramsperger-Kassel-Marcus and transition state theories

Infrared multiphoton absorption and dissociation of chloromethyltrifluorosilane molecules under the action of pulsed transversely excited atmospheric pressure CO2 laser were experimentally studied. Dissociation products were analyzed. The dissociation proceeds via chlorine atom transfer from carbon to silicone. High degrees of silicon isotope separation were achieved. The presence of a-chlorine atom in a silicon organic compound brings about a significant improvement in multiple photon dissociation characteristics and an essential increase in isotopic selectivity.

Infrared multiple photon dissociation of chloromethyltrifluorosilane.

In recent years there have been many investigations in the field of organosilicon compounds containing halogen-substituted organic groups. These investigations offer prospects of the use of these compounds in the synthesis of polyorganosiloxanes. The extensive data on methods of synthesis of halogen derivatives of alkyl(or aryl)halogenosilanes and tetrasubstituted silanes, their properties, and use are scattered in many periodicals. Monographs and review articles have so far examined only isolated aspects of the chemistry of organosilicon compounds. This has stimulated us to survey the accumulated experimental results, the analysis of which even now allows definite regularities to be found in the occurrence of certain reactions and processes in the synthesis and conversions of halogen derivatives of organosilicon compounds. There is a bibliography of 677 references.

https://iopscience.iop.org/article/10.1070/RC1969v038n03ABEH001737/pdf

C. Parkinson

Papers

Kinetics of the thermal decomposition of polyfluoroalkylsilicon compounds