Loss Of HF Research Articles

Gas-Phase Basicities Around and Below Water Revisited

This work employs Fourier transform ion cyclotron resonance (FT-ICR) and the Gaussian quantum chemistry composite methods W1 and G2 to experimentally and computationally analyze gas-phase basicities (GB) for a series of weak bases in the basicity region around and below water. The study aims to clarify the long-standing discrepancy between reported GB values for weak bases obtained via high-pressure mass spectrometry (HPMS) and ICR; the ICR scale is observed to be more than 2 times contracted compared to the HPMS scale. The computational results of this work support published HPMS data. This agreement improves with increasing sophistication of the computational method and is excellent at the W1 level. Several equilibria were also re-examined experimentally using FT-ICR. In the experiments with some polyfluorinated weak bases (hexafluoro-2-propanol and nonafluoro-2-methyl-2-propanol), it was found that two protonation processes compete in the gas phase: protonation on oxygen and protonation on fluorine. In these species, protonation on fluorine proceeds faster and is statistically favored over protonation on oxygen but leads to cations that are thermodynamically less stable than oxygen-protonated cations. The process may also lead to the irreversible loss of HF. The rearrangement of fluorine-protonated cations to oxygen-protonated cations is very slow and is further suppressed by the process of HF abstraction. These results at least partially explain the discrepancy between published HPMS data and earlier FT-ICR findings and call for the utmost care in using FT-ICR for gas-phase basicity measurements of heavily fluorinated compounds. The narrower dynamic range of ICR necessitates the measurement of several problematic bases and produces some differences between the ICR results in the present work and the published HPMS data; the wider dynamic range allows HPMS to overcome these difficulties in connecting the ladder.

Cationic Noble Gas Hydrides: A Theoretical Investigation of Dinuclear HNgFNgH+(Ng = He−Xe)

Theoretical calculations at the B3LYP, MP2, and CCSD(T) levels of theory disclose the conceivable existence of cationic noble gas hydrides containing two Ng atoms. These species have a general formula of HNgFNgH(+) (Ng = He-Xe), and are the cationic counterparts of the neutral HNgF. The optimized geometries, harmonic frequencies, and bonding properties point to ion-dipole complexes between a fluoride anion and two covalent H-Ng(+) cations, best formulated as (H-Ng(+))(2)F(-). The HXeFXeH(+) is also isoelectronic with the recently experimentally observed HXeOXeH (Khriachtchev et al. J. Am. Chem. Soc. 2008, 130, 6114-6118). The resulting HNgFNgH(+) are thermochemically stable with respect to dissociation into HNg(+) + HNgF and HNg(+) + H + Ng + F, but are largely unstable with respect to both the loss of HF (with formation of HNg(+) + Ng) and H(2)F(+) (with formation of two Ng atoms). These decompositions pass through bent transition structures, and only the heaviest HArFArH(+), HKrFKrH(+), and HXeFXeH(+) are protected by energy barriers large enough (ca. 10-15 kcal mol(-1)) to support their conceivable metastability. In line with other series of noble gas compounds, the neon cation HNeFNeH(+) is the least stable among the various HNgFNgH(+).

Unimolecular Rate Constant and Threshold Energy for the HF Elimination from Chemically Activated CF3CHFCF3

Combination of CF(3)CHF and CF(3) radicals at room temperature generated chemically activated CF(3)CHFCF(3) molecules with 95 +/- 3 kcal/mol of internal energy that decompose by loss of HF, initially attached to adjacent carbons, with an experimental unimolecular rate constant of (4.5 +/- 1.1) x 10(2) s(-1). Density functional theory was used to model the unimolecular rate constant for HF elimination, k(HF), to determine a threshold energy of 75 +/- 2 kcal/mol.

Variations of Sr–Nd–Hf isotopic systematics in basalt during intensive weathering

The Sr–Nd–Hf isotopic compositions of both saprolites and parent rocks of a profile of intensively weathered Neogene basalt in Hainan, South China are reported in this paper to investigate changes of isotopic systematics with high masses. The results indicate that all these isotopic systematics show significant changes in saprolites compared to those in corresponding parent rocks. The 87Sr/ 86Sr system was more seriously affected by weathering processes than other isotope systems, with ε Sr drifts 30 to 70 away from those of the parent rocks. In the upper profile (> 2.2 m), the Sr isotopes of the saprolites show an upward increasing trend with ε Sr changing from ~ 50 at 2.2 m to ~ 70 at 0.5 m, accompanying a upward increasing of Sr concentrations, from ~ 10 μg/g to ~ 25 μg/g. As nearly all the Sr of the parent rock has been removed during intensive weathering in this profile, the upward increasing of Sr concentrations in the upper profile suggests import of extraneous Sr. Rainwater in this region, which enriches in Sr (up to 139 μg/L) from seawater, may be the important extraneous source. Thus, the Sr isotopes of the saprolites in the upper profile may be mainly influenced by import of extraneous materials, and the Sr isotopic characteristics may not be retained. In contrast, the ε Nd and ε Hf of the saprolites drift only 0–2.6 and 0–3.7 away from the parent rocks, respectively. The negative drifts of the ε Nd and ε Hf are coupled with Nd and Hf losses in the saprolites; i.e., larger proportions of Nd and Hf loss correspond to lower ε Nd and ε Hf. Compared with the relative high Nd and Hf concentrations of the saprolites, the contributions of extraneous Nd and Hf both from wet and dry deposits of aeolian input are negligible. Thus, the ε Nd and ε Hf changes in the profile are mainly resulted from consecutive removal of the Nd and Hf. Calculation indicates that the 143Nd/ 144Nd and 176Hf/ 177Hf ratios in saprolites are all significantly lower than their initial values in the parent rock. Simply removing part of the Nd and Hf by incongruent decomposing some of the minerals may not account for this. Fractionation should be happen, which 143Nd and 176Hf may be preferentially removed from the profile relative to 144Nd and 177Hf during intensive chemical weathering, resulting in lower 143Nd/ 144Nd and 176Hf/ 177Hf ratios in saprolites relative to the parent rock, even though details for this process is not known. A positive correlation is observed between the ε Nd and ε Hf of the saprolites. Interestingly, the saprolites with a net loss of Nd and Hf in the upper profile show good positive correlation, and the regression line parallels the terrestrial array. By contrast, saprolites with a net gain of Nd and Hf in the lower profile generally show higher ε Hf values at a given ε Nd value, and the regression line between these ε Nd and ε Hf appears to parallel the seawater array. This supports the hypothesis that the contribution of continental Hf from chemical weathering release is the key to the obliquity of the seawater array away from the terrestrial array of the global ε Nd and ε Hf correlation. Our results also indicate that caution is needed when using ε Sr, ε Nd, and ε Hf to trace provenances for sediments and soils.

Enhanced Collision-Induced Decomposition Efficiency and Unraveling of Fragmentation Pathways for Anionic Adducts of Brevetoxins in Negative Ion Electrospray Mass Spectrometry

Brevetoxins are a group of natural neurotoxins characterized by polyether ring systems that are found in the blooms of red tide algae. In a conventional water/organic solvent system, without any other additives, deprotonated molecules of brevetoxins do not appear in high abundance in negative mode electrospray mass spectrometry (ES-MS) due to lack of acidic functional groups; thus, they are not well-suited for collision-induced decomposition (CID) experiments in negative mode electrospray. In this study, several anions were tested for their abilities to form anionic adducts by mixing ammonium salts of these anions with brevetoxin-2 and brevetoxin-3. Under CID, [M + Cl](-), [M + Br](-), [M + OAc](-), [M + HCOO](-), and [M + NO(3)](-) adducts all produced only the respective anions in CID experiments and thus provided no structural information. In contrast, upon CID, both [M + F](-) and [M + HCO(3)](-) precursor adducts gave structurally informative fragment peaks that exhibited similarities to those of [M - H](-) ions, which indicated that the first step in gas-phase decomposition of these anionic adducts was loss of neutral HF or H(2)CO(3) molecules, respectively, leaving deprotonated brevetoxin ([M - H](-)) to undergo consecutive fragmentations. In comparison to bicarbonate, fluoride formed adducts in higher abundance and provided more fragment peaks, thus more structural information, in MS/MS experiments. It is therefore the anion of choice to study brevetoxins in negative mode electrospray mass spectrometry using the anion attachment approach. The detailed fragmentation mechanisms are discussed, and diagnostic product ions are proposed for the brevetoxin-2 side chain (m/z 95, 133, and 151), the brevetoxin-3 side chain (m/z 97, 135, and 153), and the type-B brevetoxin backbone (m/z 725, 739, 741, and 797). To test the developed methodology, a sample of brevetoxin-2 subjected to in vitro microsomal incubation was analyzed, and a reduction product of the substrate was confirmed to have the structure of brevetoxin-3.

Unusual features in electron attachment to chlorodifluoroacetic acid (CClF 2COOH): Strong dissociative electron attachment near 0 eV and associative attachment at 0.75 eV

Electron attachment to gas phase CClF 2COOH (M) under collision free conditions exhibits very unusual features as the non-decomposed parent anion M − (associative attachment) is observed on the mass spectrometric time scale at a resonance located at 0.75 eV while strong dissociative electron attachment (DEA) reactions already occur within a resonant feature close to 0 eV. Long lived parent anions M − are usually only formed (if at all) at energies close to 0 eV and when no DEA channels are energetically accessible. The two by far dominant DEA reactions are due to the cleavage of the C–Cl bond with the excess charge localised on either of the fragments to form the closed shell anions CF 2COOH − or Cl −. Electron attachment near 0 eV also leads to more complex DEA reactions like the loss of HF or CF 2, etc., which are associated with substantial geometrical and electronic rearrangement. The thermal attachment rate constant is derived by means of an electron swarm experiment as k = 1.5 × 10 −10 cm 3 molec. −1 s −1.

Analysis of fluorotelomer alcohols in soils: Optimization of extraction and chromatography

This article describes the development of an analytical method for the determination of fluorotelomer alcohols (FTOHs) in soil. The sensitive and selective determination of the telomer alcohols was performed by extraction with methyl tert-butyl ether (MTBE) and analysis of the extract using gas chromatography with detection and quantification by mass spectrometry operated in the positive chemical ionization mode. The protonated molecular ion, [M+H] + and a fragment ion (loss of HF + H 2O) m/ z 38 less than the molecular ion were monitored to identify tentatively FTOHs in MTBE extracts of contaminated soils. The FTOHs were confirmed by treatment of the extract with a silylation reagent and observing the disappearance of the FTOH response and the appearance of peaks attributable to the [M+H] + ions of the trimethylsilyl derivatives. Mass-labeled FTOHs were used as recovery and matrix internal standards. Recovery experiments on soils shown to be free of endogenous FTOHs at instrument detection limits (IDL) of 16 fg/μL for 6:2 FTOH, 10 fg/μL for 8:2 FTOH and 14 fg/μL for 10:2 FTOH yielded a limit of quantitation (LOQ) of 190, 100, and 160 fg/μL for 6:2 FTOH, 8:2 FTOH, and 10:2 FTOH, respectively when 3 g samples of soil were extracted with 1 mL MTBE. The levels of the 6:2 FTOH, 8:2 FTOH, and 10:2 FTOH in five soils contaminated with FTOHs by exposure to the laboratory atmosphere during air drying were determined. In these air-dried soils, concentrations of FTOHs ranged from non-detectable to 3600 fg/μL (0.6 ng/g) of the 6:2 FTOH in the extract of a commercial topsoil. This method was used to determine even and odd numbered FTOHs from 6:2 through 14:2 in soils from fields that had received applications of sewage sludge. Concentrations of FTOHs in these sludge-applied soils ranged as high as 820 ng/g of dry soil for the 10:2 FTOH.

Collision-Induced Dissociation Studies of Alkali Metal Adducts of Tetracyclines and Anti-Viral Agents by Electrospray Ionization, Hydrogen/Deuterium Exchange and Multiple Stage Mass Spectrometry

The collision induced dissociation (CID) mass spectra were obtained for the X(+)-adducts (X=Na(+) or Li(+)) of five tetracyclines, four pyrimidine and three purine derivatives and their fully D-exchanged species in which the labile hydrogens were replaced by deuterium by either gas phase or liquid phase exchange. The CID spectra were obtained for [M + Na](+) and [M + Li](+) and the exchanged analogs, [M(D) + Na](+) and [M(D) + Li](+), and compositions of product ions and mechanisms of decomposition were determined by comparison of the MS(n) spectra of the undeuterated and deuterated species. Metal ions are bound to the base of purine and pyrimidine antiviral agents and dissociate primarily to give the metal complexes of the base [B + X](+). For vidarabine monophosphate, however, the metal ions are bound to the phosphate group, resulting in unique and characteristic cleavage reactions not observed in the uncomplexed system, and dissociate through the loss of phosphate and/or phosphate metal ion complex. The [B + X](+) of these antiviral agents are relatively stable and show no or little fragmentation compared to [B + H](+). The CID of [B + X](+) of guanine derivative occurs mainly through elimination of NH(3) and that of trifluoromethyl uracil dissociates primarily through the loss of HF. For tetracyclines, metal ions are bound to ring A at the tricarbonylmethyl group and dissociate initially by the loss of NH(3)/ND(3) from [M(H) + X](+) and [M(D) + X](+). The CID spectra of [M + X](+) of tetracyclines are somewhat similar to those of [M + H](+). The dominant fragments from the metal complexes of these compounds are charge remote decompositions involving molecular rearrangements and the loss of small stable molecules. Additionally, tetracyclines and the antiviral agents show more selectivity towards Li+ ion than the corresponding complexes with Na(+) or K(+).

Overtone-Induced Degradation of Perfluorinated Alcohols in the Atmosphere

Perfluorinated alcohols (PFOHs) are thermally unstable and degrade via loss of HF, ultimately forming perfluorocarboxylic acids. Experiments and calculations of the high activation barrier for the decomposition of CF3OH suggest that the reaction occurs exclusively heterogeneously, perhaps with the involvement of water. Here, we use density functional theory calculations to show that PFOHs may readily complex with water and are expected to be present as a few percent of the total PFOH concentration under ambient atmospheric conditions. The presence of water lowers the HF elimination barrier sufficiently that excitation to low-lying O-H vibrational overtone levels (vOH >or= 3) may cause reaction. Photolysis rate constants for CF3OH x H2O and CF3CF2OH x H2O were estimated to be 6.1 x 10(-8) and 5.6 x 10(-8) s(-1), respectively. PFOH-water complexes should undergo degradation much faster than the corresponding gas-phase unimolecular decomposition of PFOHs, which requires excitation into the vOH = 5 or 6 vibrational level. Overtone-driven gas-phase reactions of PFOH-water complexes could be moderately competitive with heterogeneous reactions with water in dry locations. Overtone-induced degradation of PFOHs is likely a modest atmospheric source of PFCAs to the environment.

Elucidation of urinary metabolites of fluoxymesterone by liquid chromatography‐tandem mass spectrometry and gas chromatography‐mass spectrometry

The suitability of liquid chromatography tandem mass spectrometry (LC-MS/MS) and gas chromatography mass spectrometry (GC-MS) for the elucidation of fluoxymesterone metabolism has been evaluated. Electrospray ionization (ESI) and collision induced dissociation (CID) fragmentation in LC-MS/MS and electron impact spectra (EI) in GC-MS have been studied for fluoxymesterone and two commercially available metabolites. MS(n) experiments and accurate mass measurements performed by an ion-trap analyser and a QTOF instrument respectively have been used for the elucidation of the fragmentation pathway. The neutral loss scan of 20 Da (loss of HF) in LC-MS/MS has been applied for the selective detection of fluoxymesterone metabolites. In a positive fluoxymesterone doping control sample, 9 different analytes have been detected including the parent compound. Seven of these metabolites were also confirmed by GC-MS including 5 previously unreported metabolites. On the basis of the ionization, the CID fragmentation, the accurate mass of the product ions and the EI spectra of these analytes, a tentative elucidation as well as a proposal for the metabolic pathway of fluoxymesterone has been suggested. The presence of these compounds has also been confirmed by the analysis of five other positive fluoxymesterone urine samples.

Fluorine reactivity in difluoromethylimidazoles

A difluoromethyl substituent attached directly to an imidazole ring is very reactive toward basic hydrolysis. A correlation of rate of fluoride loss with increasing pH is consistent with a mechanism that involves initial ionization of the imidazole NH, formation of an intermediate azafulvene by loss of HF, and reaction of the intermediate with solvent water.

Unimolecular reactions of halogeno phenylarsenium ions: Kinetic energy release during the elimination of halogen hydride

The four dihalogeno phenylarsanes C 6H 5AsF 2, 1, C 6H 5AsCl 2, 2, C 6H 5AsBr 2, 3, and C 6H 5AsI 2, 4, produce in the 70 eV-EI mass spectra by loss of a halogen atom abundant halogeno phenylarseniun ions C 6H 5As +–X, 1a +– 4a +. The further fragmentation reactions of ions 1a +– 4a + are elimination of a molecule halogen hydride HX and/or loss of a halogen atom X . The preferred route of fragmentation depends clearly on the strength of the As–X bond. The metastable fluoro ion 1a + and chloro ion 2a +, respectively, fragment only by loss of HF and HCl, the metastable bromo derivative 3a + exhibits losses of HBr and Br of about equal intensity, and the metastable iodo ion 4a + fragments only by loss of an I atom. The loss of HX is associated with a large kinetic energy release (KER) which yield a dish-topped peak in the MIKE spectrum of 1a + (〈 T〉 = 845 meV) and 2a + (〈 T〉 = 550 meV) and a broad round-topped peak on the MIKE spectrum of 3a + (〈 T〉 = 369 meV). Theoretical calculations (UBHLYP/6-311 + G(2d,p)/-/UBHLYP/6-31 + G(d)) confirm that the elimination of HX requires an enthalpy of activation Δ H #, and that in the case of 3a + this Δ H # and the reaction enthalpy for loss of Br are of similar size. The Δ H # of HX elimination is also responsible for the reverse enthalpy of activation Δ H rev # and the KER during this process. The observed 〈 T〉 amounts to 78% ( 1a +), 55% ( 2a +), and 40% ( 3a +) of the calculated value of Δ H rev # . Thus, the KER as well as the distribution of the KER (KERD) and the competition between elimination of HX and loss of X are very specific for the halogen ligand at the As atom. Metastable (4-fluorophenyl) arsenium ions 1b +, F–C 6H 4As +–H, and (4-chlorophenyl) arsenium ions 2b +, Cl–C 6H 4As +–H +, eliminate HF or HCl with virtually identical KERD as metastable 1a + or 2a +, C 6H 5As +–Cl, proving an identical transition state for both isomers. Accordingly, 1b + and 2b + rearrange to 1a + and 2a + prior to HCl elimination. Such a rearrangement by a reductive elimination/oxidative insertion of As + into C H and C X bonds has been observed before and appears to be typical of arylarsane radical cation and arylarsenium cations.

Gas-phase ion chemistry of Ti(O-i-Pr)4

The positive and negative gas-phase ion chemistry of Ti(O-i-Pr)4 was investigated at low pressures by FT-ICR. The fragment ion, (i-PrO)3Ti-O+=C(H)Me, reacts with the parent neutral by proton transfer and by a nucleophilic addition–elimination reaction. The nature of the fragment ion and the ensuing ion–molecule reactions clearly indicate that Ti(O-i-Pr)4 exists as a monomer in the gas phase. In the negative ion mode, F– was found to react easily with Ti(O-i-Pr)4 to yield the pentacoordinated complex FTi(O-i-Pr)4– ion. This hypervalent Ti species undergoes a series of sequential fragmentations induced by IR multiphoton excitation. The first step is unusual because two channels are observed by IRMPD: one involves loss of HF, and the other loss of i-PrOH. The subsequent dissociation processes are characterized by progressive elimination of propene giving rise to a number of different titanaoxirane-containing anions with the general formula [(η2-CMe2O)Ti(OH)3–n(i-PrO)n]–. FTi(O-i-Pr)4– was also observed to undergo multiple alkoxide–fluoride exchanges with BF3 leading to the eventual formation of TiF5–.Key words: titanium tetraisoproxide, gas-phase ion chemistry, hypervalent Ti, ion–molecule reactions, IRMPD.

Bond-Forming Reactions of Dications with Molecules: A Computational and Experimental Study of the Mechanisms for the Formation of HCF2+ from CF32+ and H2

The QCISD and QCISD(T) quantum chemical methods have been used to characterize the energetics of various possible mechanisms for the formation of HCF2+ from the bond-forming reaction of CF3(2+) with H2. The stationary points on four different pathways leading to the product combinations HCF2+ + H+ + F and HCF2+ + HF+ have been calculated. All four pathways begin with the formation of a collision complex [H2-CF3]2+, followed by an internal hydrogen atom migration to give HC(FH)F2(2+). In two of the mechanisms, immediate charge separation of HC(FH)F2(2+) via loss of either HF+ or a proton, followed by loss of an F atom, yields the experimentally observed bond-forming product HCF2+. For the other two mechanisms, internal hydrogen rearrangement of HC(FH)F2(2+) to give C(FH)2F(2+), followed by charge separation, yields the product CF2H+. This product can then overcome a 2.04 eV barrier to rearrange to the HCF2+ isomer, which is 1.80 eV more stable. All four calculated mechanisms are in agreement with the isotope effects and collision energy dependencies of the product ion cross sections that have been previously observed experimentally following collisions between CF3(2+) and H2/D2. We find that in this open-shell system, CCSD(T) and QCISD(T) T1-diagnostic values of up to 0.04 are acceptable. A series of angularly resolved crossed-beam scattering experiments on collisions of CF3(2+) with D2 have also been performed. These experiments show two distinct channels leading to the formation of DCF2+. One channel appears to correspond to the pathway leading to the ground state 1DCF2+ + D+ + F product asymptote and the other to the 3DCF2+ + D+ + F product asymptote, which is 5.76 eV higher in energy. The experimental kinetic energy releases for these channels, 7.55 and 1.55 eV respectively, have been determined from the velocities of the DCF2+ product ion and are in agreement with the reaction mechanisms calculated quantum chemically. We suggest that both of these observed experimental channels are governed by the reaction mechanism we calculate in which charge separation occurs first by loss of a proton, without further hydrogen atom rearrangement, followed by loss of an F atom to give the final products 1DCF2+ + D+ + F or 3DCF2+ + D+ + F.

Formation and Decomposition of Hydroxysiliconates in the Gas Phase

This work describes studies of the formation, structure, and dissociation of hydroxysiliconate ions. Hydroxide adduct ions can be formed in the reaction of halogenated and oxygenated silanes with hydrated hydroxide, OH-(H2O)n. Experiments with mass-selected ions indicate that at least two water solvent molecules are required in order to form a hydroxide adduct of fluorotrimethylsilane. Collision-induced dissociation, ion formation, and ion reactivity studies suggest pentavalent siliconate structures for hydroxide adducts of halogenated silanes but solvated siloxides for the oxygenated species. Electronic structure calculations find three types of hydroxide adduct ions, including the hydroxysiliconate and two forms of solvated siloxides. The relative energies of the ions and the barriers that separate them depend on the substituents on the silanes. Empirical modeling of the cross sections for collision-induced dissociation indicates that loss of HF from fluorinated hydroxide adducts occurs through a loose transition state, whereas loss of alkane/arene occurs through a tight transition state at low activation energies.

Unusual Addition Patterns in Trifluoromethylation of [60]Fullerene.

From pyrolytic trifluoromethylation of [60]fullerene with CF3CO2Ag at 300 °C we have isolated ca. sixty C60(CF3)n isomers (numbers in parentheses) as follows: n = 2 (1), 4 (8), 6 (13), 8 (21) 10 (11), 12 (5), 14 (4), twenty-one of which have been characterised by 19F NMR. Compounds with addition levels up to n = 20 have also been identified. With increasing value of n, yields decrease and the separation of compounds of similar HPLC retention time but different addend levels becomes more difficult. Many of the 19F NMR spectra show combinations of quartets and septets (the latter tending to be more downfield) due to ‘linear’ addend arrays. The spectra are consistent with addition across both 6:6- and 5:6-ring junctions [double (1,2) and single (1,6) bonds, respectively], giving corresponding coupling constants for adjacent addends of ca. 14.5 and 12.0 Hz respectively, the differences being attributable to the different 1,2- and 1,6-bond lengths. The 13C NMR spectrum of C60(CF3)2 shows the CF3 groups are in either a 1,4- or 1,6-relationship; the UV-vis band appears at 442 nm. Other unsymmetrical tetra-adducts are comprised of isolated pairs of CF3 groups. The exceptionally large number of derivatives and isomers, (much greater than in any other fullerene reaction), no dominant product, and unusual addition pattern indicates that thermodynamic stability is not of primary importance in governing product formation. EI mass spectrometry of trifluoromethylfullerenes is characterised by loss of CF3 groups, the more highly addended compounds also showing fragmentation by CF2 loss, attributable to steric compression. The CF3 group shows strong IR bands at ca. 1260 and 1190 cm−1. The compounds are stable to aq. acetone, which contrasts to the behaviour of fluorofullerenes. Trifluoromethylation by the Scherer radical (C9F19˙) gave addition of up to eight CF3 groups, together with hydrogen in some products. During EI mass spectrometry of some of these, loss of HF attributable to CF3 and H adjacency can occur, giving CF2-containing derivatives.

Gas-phase ion chemistry and ion thermochemistry of phenyltrifluorosilane

The ion/molecule reactions of phenyltrifluorosilane with F −, CH 3O − and OH − and the thermochemical properties of the resulting ions were investigated by using a flowing afterglow—triple quadrupole mass spectrometer. The silane reacts with fluoride and methoxide ions by addition, whereas the reaction with hydroxide proceeds by addition and loss of HF to form the phenyldifluorosiloxide ion. Collision-induced dissociation (CID) of the adduct ions produces predominantly phenide ion, although rearrangement processes are also observed for the methoxide adduct. CID of the siloxide ion results in direct cleavage to form the SiF 2O − ion, in addition to products formed by rearrangement. We also report the formation of the hydroxide adduct of phenyltrifluorosilane, and provide the first confirmation that activated hydroxide adducts of silanes dissociate by loss of RH. The hydride adduct of phenyltrifluorosilane is generated indirectly by the addition of fluoride to phenyldifluorosilane. Bond dissociation energies and rearrangement barriers were obtained for all ions from the energy-resolved CID cross sections. From the measured bond dissociation energies, the fluoride, hydride and methoxide affinities of phenyltrifluorosilane are determined to be 79.4±3.3 and 64.0±3.2, and 76.6±5.9 kcal/mol, respectively, and the fluoride affinity of phenyldifluorosilane is found to be 72.3±4.4 kcal/mol. The hydride affinity (HA) of phenyltrifluorosilane is comparable to that of borane, suggesting that C 6H 5SiHF 3 − is a potential hydride reducing agent in the condensed phase.

Concerning the reaction between singlet nitrenium ions and water: A computational investigation on competitive reaction paths

The reaction between singlet nitrenium ions XNH(+) (X = F and Cl) and H(2)O has been investigated by high-level of theory ab initio calculations. The geometries of the involved intermediates, transition structures, and dissociation products have been optimized at the MP2(full)/6-31G(d) level of theory, and accurate total energies have been obtained using the Gaussian-3 (G3) procedure. The reaction commences by the exothermic formation of the F-NH-OH(2) (+) and Cl-NH-OH(2) (+) intermediates, which are in turn able to undergo two distinct low-energy reaction paths, namely, the isomerization to the N-protonated isomers of the hydroxylamines F-NH-OH or Cl-NH-OH, and the eventual extrusion of HF or HCl. The competitive or alternative occurrence of these two processes strictly depends on the nature of the substituent X. In the reaction between FNH(+) and H(2)O, the energy gained in the formation of the complex F-NH-OH(2) (+) from the association between FNH(+) and H(2)O, 52.1 kcal mol(-1), is by far larger than the activation barrier for the loss of HF from F-NH-OH(2) (+), computed as 24.9 kcal mol(-1). In addition, the F-NH-OH(2) (+) intermediate requires 33.0 kcal mol(-1) to overcome the barrier for the isomerization to F-NH(2)-OH(+). Therefore, the reaction between FNH(+) and H(2)O is expected to occur practically exclusively by HF elimination with formation of the HN-OH(+) ionic product. On the other hand, for the reaction between ClNH(+) and H(2)O, it is not possible to get a definitive conclusion on the competitive or alternative occurrence of the two reaction paths. In fact, the transition structure involved in the elimination of HCl from Cl-NH-OH(2) (+) is only 3.4 kcal mol(-1) lower in energy than the transition structure for the isomerization of Cl-NH-OH(2) (+) to Cl-NH(2)-OH(+). In addition, the absolute values of the energy barriers of these two processes, 24.2 and 27.6 kcal mol(-1), respectively, are comparable with the energy gained in the formation of the complex Cl-NH-OH(2) (+) from the association between ClNH(+) and H(2)O, 24.0 kcal mol(-).1 Therefore, the ClNH(+) cation is predicted to react with water significantly slower than FNH(+).

Syntheses of selectively fluorinated cyclodecenones: the first deployment of the neutral oxy-Cope rearrangement in organofluorine chemistry.

Metallated haloalkenes were used to open epoxides in moderate to good yield. The homoallylic alcohols obtained underwent Swern oxidation to afford three gamma,gamma-difluorinated beta,gamma-enones, which reacted with either vinyllithium,2-lithio-2H-dihydropyran or another metallated haloalkene to afford substituted trans-1,2-divinylcyclohexanols of different degrees of stability. These intermediates underwent neutral thermal oxy-Cope rearrangements when heated in xylene in Ace tubes. The first-formed enols ketonised without loss of HF to afford a range of cyclodecenones in moderate to good yield; X-ray crystallography was used extensively for product characterisation. All substrates rearranged more rapidly than a cis/trans mixture of 1,2-divinylcyclohexanols.

Loss of HF from C 2H 4FO + produced from 2-hydroxy-2-trifluoromethylpropanoic acid upon electron ionization

Metastable C 2H 4FO + ions ( m/ z 63) produced by electron ionization of 2-hydroxy-2-trifluoromethylpropanoic acid CH 3C(CF 3)(OH)COOH ( 1) decompose into CH 3CO + ( m/ z 43) and HF. The corresponding peak in the MIKE spectrum is composite with translational energy release values of 0.83 eV and <1 meV. The origin of this composite peak was investigated on the basis of quantum chemical calculations. We propose that the m/ z 63 ion from 1 + consists of two isomers, i.e., CH 3C +FOH and CH 3CO +⋯FH, with the former (latter) being responsible for the broad (narrow) component of the peak. The decomposition processes of the precursor ion CH 3C +(CF 3)OH are also explored in some detail.