Search

Dissociative electron ionization (70 eV) of ethyl carbomylmethanedithioate generates m/z 77 ions of composition [H, C, S2]+. The collision-induced dissociation (CID) mass spectrum of these ions is consistent with the mercaptothiocarbonyl connectivity HSCS+ (a+). Calculations predict that some of the a+ ions may equilibrate with HC(S)S+ (b)+ ions prior to dissociation. Neutralization-reionization mass spectrum (NRMS) of these ions confirmed that neutral HSCS is stable in the rarefied gas phase. The relative, dissociation, and isomerization energies for the ions and neutrals studied at B3LYP/6-311G(d,p) and G2/G2(MP2) levels, are used to support and interpret the experimental results.

Electron ionization of rhodanine yields iminothiosulfine ions H – N  C – S – S + , 1b + , which readily communicate with the higher energy cyclic isomer H – N  CS 2 + , 1a + . CBS-QB3 and G aussian -2 model chemistries predict that one electron reduction reverses the stability order but that the (singlet) neutrals remain connected via a negligible energy barrier. Neutralization–reionization (NR) experiments demonstrate that singlet 1a and its heterocumulene isomer 1b are stable species in the gas-phase. However, the co-generated triplet species readily dissociate into 3 S 2 + + HNC . Confirmatory experimental evidence comes from charge reversal (CR) and NR experiments on the cyclic anion H – N  CS 2 − , 1a − .

The isomeric dicoordinated borinium ions CH3O–B–H+ and CH3–B–OH+ are generated upon electron ionization of trimethylborate and methyl boronic acid, respectively. The connectivity of the ions is confirmed by collision-induced dissociation experiments on magnetic deflection type tandem mass spectrometers. Neutralization–reionization experiments on these structurally characterized ions indicate that the neutral radicals CH3O–B–H· and CH3–B–OH· are viable species in the gas phase. Calculations at the G2 level of theory were performed to obtain thermochemical data on the title isomers and their main dissociation products. The calculations also provide a rationale for the moderate yield of the neutrals generated in the experiments: the vertical electron transfer processes for both systems are associated with particularly unfavourable Franck-Condon factors.

The dicoordinated borinium ion, dihydroxyborinium, B(OH) 2 + is generated from methyl boronic acid CH 3 B(OH) 2 by dissociative electron ionization and its connectivity confirmed by collisional activation. Neutralization–reionization (NR) experiments on this ion indicate that the neutral B(OH) 2 radical is a viable species in the gas phase. Both vertical neutralization of B(OH) 2 + and reionization of B(OH) 2 in the NR experiment are, however, associated with particularly unfavorable Franck-Condon factors. The differences in adiabatic and vertical electron transfer behavior can be traced back to a particular π stabilization of the cationic species compared to the sp 2 -type neutral radical. Thermochemical data on several neutral and cationic boron compounds are presented based on calculations performed at the G2 level of theory.

[Si,C,N,O]+ and [Si,C,N,S]+ cations formed upon electron ionization of trimethylsilyl isocyanate and isothiocyanate, respectively, are probed by tandem mass spectrometry. In the case of [Si,C,N,O]+, the experimental data suggest that the isocyanato group remains intact upon ionization such that silicon isocyanate SiNCO+ is formed. Neutralization-reionization mass spectrometry indicates that also neutral SiNCO is a viable molecule in the gas phase. Instead, partial isomerization to SiSCN+ is indicated for the sulfur analog. Because of this structural dichotomy, the nature of the [Si,C,N,S]+ species giving rise to the recovery signal in the neutralization-reionization experiments remains uncertain.