A novel mechanism for reactions of thiirane with the thiirane radical cation. An experimental and ab initio study

Abstract

An experimental and computational study of the ion-molecule reactions initiated by the reaction of SC2H4"* 1" with SC2H4 has been carried out. The dimer ion is observed in a hybrid drift tube/ion source under chemical ionization conditions at low temperatures and high pressures. However, the ion intensity is much lower than expected for a product containing a stable two-center three-electron (2c-3e) S/.S bond. Above room temperature, ion intensities for m/z 92 S2C2H4'"1", m/z 124 S3C2H4"1", m/z 156 S4C2H4'"1", and m/z 184 S4C4H8•"1" dominate. The first three ions result from sequential association of SC2H4'"1" with SC2H4 followed by elimination of ethylene, while the latter ion (m/z 184) is due to the association of S3C2H4•"1" with SC2H4 without loss of ethylene. As the temperature is lowered, clustering is promoted relative to reaction channels involving loss of ethylene. The experimental results are not in full agreement with a published ab initio study which found that the product channel was 33-kJ/mol endothermic with respect to reactants. The present ab initio calculations indicate that another reaction channel is possible, resulting in a fourmembered-ring C-S2C2H44", which is exothermic by 43.0 kJ/mol. The potential energy surface for this channel, including transition states, was computationally studied in detail. An interesting aspect of this mechanism is the stepwise addition of sulfur atoms forming successively larger rings which continues until the six-membered-ring S4C2H44, is formed.

Studies of Two-Center Three-Electron S∴S Bonds in [n-Pr2S∴Sn-Pr2]+ and [i-Pr2S∴Si-Pr2]+: Thermochemistry of Adduct Formation and MS/MS Metastable and Collision-Induced Dissociation Spectra of the Adducts

“…Drewello et al 11 had interpreted the presence of both peaks in the CID spectra to mean that the S-C bonds and the S∴S bond have similar bond strengths. Ekern et al 2 computed in [c-C 2 H 4 S∴Sc-C 2 H 4 ] + the endothermicity of the S-C bond breaking to be 82.2 kJ/mol. In this cyclic system, ring strain has an effect on the bond dissociation energy of the S-C bond compared to a noncyclic S-C bond, which is expected to be higher in energy.…”

“…It was shown in the cyclic case that as the S-C bond was breaking, the S-S interaction became stronger because the bond order increased from 1/2 to 1. 2 …”

“…[1][2][3][4][5][6] 2c-3e bonds were first described by Linus Pauling in 1931. 7 The molecular orbital representation of the 2c-3e bond indicates that two electrons occupy a bonding orbital and one electron occupies an antibonding orbital.…”

“…To better understand these interactions, our group has been investigating 2c-3e S∴S bonded ions in which the two energy levels are of similar energy. 1,2,5 The calculated S∴S bond energies of [Me 2 S∴SMe 2 ] + , [Et 2 S∴SEt 2 ] + , and [Et 2 S∴SMe 2 ] + are presented in Table 1. 1,5 These bond energies are in the range of 39-47% of a typical 2c-2e S-S bond.…”

Isolation and reversible dimerization of a selenium–selenium three-electron σ-bond

“…Structure determination and analysis is one of the most useful and direct methods for studies of odd-electron bonds. Although many three-electron s-bonding systems X'X and X'Y (X, Y ¼ He, N, S, P, halogen and so on) have been investigated in the gas phase, solution and solid matrix, and characterized by various spectroscopic techniques in conjunction with theoretical calculations [23][24][25][26][27][28][29][30][31] , few of them are roomtemperature stable because they are either too reactive or dimerize in the solid state. Only three examples have been isolated and structurally characterized by single-crystal X-ray diffraction (Fig.…”