Infrared Multiphoton Dissociation Spectra as a Probe of Ion Molecule Reaction Mechanism:  The Formation of the Protonated Water Dimer via Sequential Bimolecular Reactions with 1,1,3,3−Tetrafluorodimethyl Ether

Abstract

The gas-phase ion-molecule reactions of 1,1,3,3-tetrafluorodimethyl ether and water have been examined using Fourier transform ion cyclotron resonance mass spectrometry, infrared multiphoton dissociation (IRMPD) spectroscopy, and ab initio molecular orbital calculations. This reaction sequence leads to the efficient bimolecular production of the proton-bound dimer of water (H5O2+). Evidence for the dominant mechanistic pathway involving the reaction of CF2H-O=CHF+, an ion of m/z 99, with water is presented. The primary channel occurs via nucleophilic attack of water on the ion of m/z 99 (CF2H-O=CHF+), to lose formyl fluoride and yield-protonated difluoromethanol (m/z 69). Association of a second water molecule with protonated difluoromethanol generates a reactive intermediate that decomposes via a 1,4-elimination to release hydrogen fluoride and yield the proton-bound dimer of water and formyl fluoride (m/z 67). Last, the elimination of formyl fluoride occurs by the association of a third water molecule to produce H5O2+ (m/z 37). The most probable isomeric forms of the ions with m/z 99 and 69 were found using IRMPD spectroscopy and electronic structure theory calculations. Thermochemical information for reactant, transition state, and product species was obtained using MP2(full)/6-311+G**//6-31G* level of theory.

Consecutive Fragmentation Mechanisms of Protonated Ferulic Acid Probed by Infrared Multiple Photon Dissociation Spectroscopy and Electronic Structure Calculations

“…Relative Gibbs free energies (298 K) are reported in kJ mol −1 Electronic structure calculations have been performed using the Gaussian 09 software package [32]. All geometry optimizations and associated frequency calculations have been performed at the B3LYP/6-311+G(d,p) level of theory, which has been shown to be a reliable protocol, with a good compromise between accuracy and cost, for smaller systems such as those described here [13,14,16,24,[33][34][35][36]. All harmonic frequencies obtained at this level of theory were scaled by 0.9679 [37] in order to compensate for errors arising from the use of a harmonic oscillator approximation in calculating the frequencies, as well as long range electron correlation effects.…”

The sodium cation-bound dimer of theophylline: IRMPD spectroscopy of a highly symmetric electrostatically bound species

“…All proposed isomers of the SCBD of theophylline were optimized using density functional theory (DFT), employing the B3LYP exchange-correlation functional and the 6-311+G(d,p) basis set. B3LYP is known to be a relatively reliable and economical computational method and is extensively employed in the investigation of small and medium size molecules [49,[51][52][53][54][55][56]. All harmonic frequencies obtained at this level of theory were scaled by 0.9679 [57] in order to compensate for errors arising from the use of a harmonic oscillator approximation in calculating the frequencies, as well as, long range electron correlation effects.…”

“…It is well established that hybrid DFT methods such as B3LYP generally outperform local or gradient-corrected DFT, and MP2 for the prediction of fundamental frequencies and their associated infrared intensities [7,13,56,[59][60][61][62][63][64][65][66]. Fundamental frequencies calculated by the MP2 method are significantly more costly and sometimes less accurate than those produced by B3LYP, thus, all geometry optimizations and calculated frequencies reported here have been obtained using the B3LYP method.…”

Proton transfer reactions of halogenated compounds: Using gas chromatography/Fourier transform ion cyclotron resonance mass spectrometry (GC/FT-ICR MS) and ab initio calculations

“…The H 5 O 2 + species is only observed when CHCl 3 elutes off the GC in CI/GC/FT-ICR MS experiments and H 2 O is one of the CI reagents and not in EI/GC/FT-ICR MS type experiments. The formation of the protonated dimer (H 5 O 2 + ) has been observed in FT-ICR mass spectrometry studies of 1,1,3,3-tetrafluorodimethylether (TFDE) in bimolecular reactions [69]. In addition, we do not believe that the pressure in our ICR cell ever approaches that of a SIFT experiment of ∼0.5-1 Torr for the formation of H 5 O 2 + by a ter-body association mechanism to be effective.…”