A crossed beam and ab initio investigation on the formation of vinyl boron monoxide (C2H3BO; X1A′) via reaction of boron monoxide (11BO; X2Σ+) with ethylene (C2H4; X1Ag)

Abstract

The reaction dynamics of the boron monoxide radical ((11)BO; X(2)Σ(+)) with ethylene (C(2)H(4); X(1)A(g)) were investigated at a nominal collision energy of 12.2 kJ mol(-1) employing the crossed molecular beam technique and supported by ab initio and statistical (RRKM) calculations. The reaction is governed by indirect scattering dynamics with the boron monoxide radical attacking the carbon-carbon double bond of the ethylene molecule without entrance barrier with the boron atom. This addition leads to a doublet radical intermediate (O(11)BH(2)CCH(2)), which either undergoes unimolecular decomposition through hydrogen atom emission from the C1 atom via a tight transition state located about 13 kJ mol(-1) above the separated products or isomerizes via a hydrogen shift to the O(11)BHCCH(3) radical, which also can lose a hydrogen atom from the C1 atom. Both processes lead eventually to the formation of the vinyl boron monoxide molecule (C(2)H(3)BO; X(1)A'). The overall reaction was determined to be exoergic by about 40 kJ mol(-1). The reaction dynamics are also compared to the isoelectronic ethylene (C(2)H(4); X(1)A(g)) - cyano radical (CN; X(2)Σ(+)) system studied earlier.

A combined crossed molecular beams and ab initio investigation on the formation of vinylsulfidoboron (C2H311B32S)

“…60 Lastly, we observed that the CM angular distribution depicts a peak intensity at around y = 831 indicating that the decomposing complex preferentially emits a hydrogen atom almost parallel to the total angular momentum vector and nearly perpendicular to the rotational plane of the decomposing complex (sideways scattering). 58 These geometrical constraints have also been identified, for instance, in the reactions of isovalent cyano (CN) 61 and boron monoxide ( 11 BO) 26 radicals with ethylene.…”

“…However, if we assume that the available energy is equilibrated among molecular degrees of freedom before the reaction occurs and considering that energy is conserved, the rate constants for the reaction steps can also be predicted by RRKM theory. 25,26 These calculations suggest that 92% of the vinylsulfidoboron molecule (C 2 H 3 BS) is formed via the unimolecular decomposition of i2, while only 8% of the final product is formed via the fragmentation of i1.…”

“…The flash vacuum pyrolysis of triphenyl-and trimethylboroxin in argon matrix and at low temperature below 20 K followed by gas phase products trapping yielded phenyl(oxo)borane (C 6 H 5 BO) and methyl(oxo)borane (CH 3 BO), which were characterized by IR spectroscopy. 24 In recent years, our group has systematically investigated the reactions of the boron monoxide radical with unsaturated hydrocarbons such as acetylene (C 2 H 2 ), 25 ethylene (C 2 H 4 ), 26 methylacetylene (CH 3 CCH), 27 diacetylene (HCCCCH), 28 dimethylacetylene (CH 3 CCCH 3 ), 29 as well as benzene (C 6 H 6 ) 30 under single collision conditions utilizing a crossed molecular beams machine. These bimolecular gas phase reactions led to the identification of previously unknown organoboronyl molecules formed via de-facto barrierless addition of the boron monoxide radical to the p-electron density of the unsaturated hydrocarbons via indirect scattering dynamics, followed by atomic hydrogen and/or methyl group loss in overall exoergic reactions (Fig.…”

The role of isovalency in the reactions of the cyano (CN), boron monoxide (BO), silicon nitride (SiN), and ethynyl (C2H) radicals with unsaturated hydrocarbons acetylene (C2H2) and ethylene (C2H4)

“…Here, we review the results of our crossed molecular beam experiments of four isovalent X 2 S + radicals -CN, 15,17,28 BO, 40,41 SiN, 37,38 and C 2 H 28,55,56 -with simple prototypical hydrocarbon reactants, acetylene (C 2 H 2 ) and ethylene (C 2 H 4 ). This approach will help us to elucidate generalized concepts on the chemical dynamics and the similarities and differences of the underlying mechanisms of the reactions of isovalent radicals with unsaturated hydrocarbons in extreme environments and their role in the formation of substituted hydrocarbons.…”

“…6,39 Finally, in rocket propulsion systems the combustion of boron offers three times the energy release than carbon, however boron readily forms oxides like boron monoxide that disrupt the combustion process by undergoing competing reactions with fuel components such as unsaturated hydrocarbons. [40][41][42][43] The multitude of simultaneous reactions in extreme environments makes for a difficult area of study. Only by systematically investigating the chemical dynamics of each contributing elementary reaction under single collision conditions will we be able to effectively model these complex environments.…”