Thermochemistry of fluorinated main group systems in the gas phase
Abstract
Gas-phase thermochemistry and reactivity for several novel main group species including silanes and xenon-containing species is discussed. Novel species were prepared in a flowing afterglow triple quadrupole mass spectrometer. Prepared species are chiefly characterized by means of collision-induced dissociation (CID) and energy-resolved mass spectrometry (ERMS). Experimentally determined energetics are associated with supplemental thermochemistry to gain insight as to the electronic structure and bonding of fluorinated main group systems. The reaction of phenyltrifluorosilane (PhSiF3) with several different nucleophiles including fluoride and methoxide generated new siliconate species. The hydride affinity of PhSiF3 was determined to be comparable to the hydride affinity of BH3, suggesting that PhSiHF3 - may be a potential hydride donor in the condensed phase. The fluoride affinity of PhSiF3 was found to be comparable to that of BF 3, indicating that PhSiF3 and BF3 are comparable Lewis acids. Thermochemical measurements for the dissociation of RSi(CH3) 3F- (R = EtO, CF3CH2O, iPrO, Me3SiO and Me3SiNH) to lose R - and FSi(CH3)3 were used to assess the feasibility of fluoride-induced desilylation within the gas phase. Decompositions of hydroxyfluorosiliconates (RSi(CH3) 2FOH-, R = Me, Ph) were studied. RSi(CH3) 2FOH- undergoes CID to competitively lose RH, CH 4 and HF. Empirical modeling of these dissociations indicate that loss of HF occurs through a loose transition state, whereas loss of alkane/arene occurs through a tight transition state at low activation energies. Xenon-containing species were prepared and studied in the gas phase. The bond dissociation energy of XeF+ was directly measured for the first time. XeF3- dissociates to give F - and XeF2. From experimental data and calculations, the electronic structure of XeF3- is discussed.
Degree
Ph.D.
Advisors
Wenthold, Purdue University.
Subject Area
Chemistry|Chemistry
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