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Papers by Nicole Eyet
International Journal of Mass Spectrometry, 2021
Abstract The temperature- and pressure-dependent kinetics of Co+(CH3Br)n (n = 0,1) + CH3Br are me... more Abstract The temperature- and pressure-dependent kinetics of Co+(CH3Br)n (n = 0,1) + CH3Br are measured from 300 to 600 K and from 0.2 to 0.5 Torr. Results are interpreted using density functional calculations and modeled with statistical theory. In the n = 0 case, the associative product Co+(CH3Br) dominates with a rate constant between 5 and 30% of the collisional value, while a minor channel yields CoBr+ + CH3 with a rate constant increasing with temperature. 0K bond dissociation energies (BDE) are determined for Co+-Br (2.8 ± 0.1 eV) and Co+-CH3Br (2.4 ± 0.25 eV). Ligation of Co+ (i.e. n = 1) significantly increases the bimolecular reaction rate constant. CoBr+(CH3Br) + CH3 is formed and the reaction has a positive temperature dependence. Interestingly, this rate constant decreases with increasing pressure due to competition of the association channel. Ligation increases the (CH3Br)Co+-Br BDE (3.0 ± 0.1 eV) relative to Co+-Br, but decreases the (CH3Br)Co+-CH3Br BDE (1.95 ± 0.25) relative to Co+-CH3Br. Both bimolecular reactions proceed by a metal-insertion mechanism with a significantly submerged transition state that does not affect the kinetics. Instead, the endothermicity of the reaction is rate-limiting. Discussion about how energy, impact parameter, and angular momentum affect specific rate constants for dissociation to reactants, reaction to products, and association are presented.
3 , probably because of the extremely explosive character of the compound. There are 4 exothermic... more 3 , probably because of the extremely explosive character of the compound. There are 4 exothermic channels in electron attachment to ClN 3 , but only the Cl − channel was observed to occur at 298 and 400 K in the present work. Electron attachment rates were measured to be 3.5 × 10 −8 and 4.5 × 10 −8 cm 3 s −1 at 298 K and 400 K, ±35%, using a FALP apparatus. The activation energy for the reaction is 24 ± 10 meV. The reactivity of ClN 3 with 17 negative ions and 21 positive ions has been investigated at 300 K using a SIFT apparatus. The electron affinity, (2.48 ± 0.20 eV), proton affinity (713 ± 41 kJ mol −1), and ionization energy (> 9.6 eV) of ClN 3 were bracketed. These measurements are in agreement with results from G3 calculations. For negative ion reactions, the major product of the reactions was Cl − , while charge transfer, N − 3
International Journal of Mass Spectrometry, 2015
The reactivity of microsolvated fluoride ions, F À (CH 3 OH) 0-2 , with methyl, ethyl, n-propyl, ... more The reactivity of microsolvated fluoride ions, F À (CH 3 OH) 0-2 , with methyl, ethyl, n-propyl, and t-butyl bromide is evaluated over a broad range of temperatures. Significant decreases in reactivity are observed as either solvation or temperature increases. Increasing solvation increases sensitivity to the reaction barrier as revealed by a larger temperature dependence. These reactions are dominated by an S N 2 mechanism for the methyl bromide reaction, while the S N 2 and E2 mechanisms compete for the reactions with ethyl and n-propyl bromide reactions. The elimination mechanism, with some association, dominates the t-butyl bromide reactions. In all cases the unsolvated bromide ion is the primary ionic product. Branching ratios are discussed in both qualitative and quantitative terms for all reactions at 300 K.
International Journal of Mass Spectrometry, 2015
The reactivity of microsolvated fluoride ions, F À (CH 3 OH) 0-2 , with methyl, ethyl, n-propyl, ... more The reactivity of microsolvated fluoride ions, F À (CH 3 OH) 0-2 , with methyl, ethyl, n-propyl, and t-butyl bromide is evaluated over a broad range of temperatures. Significant decreases in reactivity are observed as either solvation or temperature increases. Increasing solvation increases sensitivity to the reaction barrier as revealed by a larger temperature dependence. These reactions are dominated by an S N 2 mechanism for the methyl bromide reaction, while the S N 2 and E2 mechanisms compete for the reactions with ethyl and n-propyl bromide reactions. The elimination mechanism, with some association, dominates the t-butyl bromide reactions. In all cases the unsolvated bromide ion is the primary ionic product. Branching ratios are discussed in both qualitative and quantitative terms for all reactions at 300 K.
The Journal of Physical Chemistry C, 2011
Recently, it was discovered that specific aluminum clusters (e.g., Al 13 À) that demonstrate enha... more Recently, it was discovered that specific aluminum clusters (e.g., Al 13 À) that demonstrate enhanced resistance to reactivity with oxygen may do so not only because of a closed electronic jellium shell as originally supposed but also because of a forbidden spin-flip in the transition state of the reaction. Herein, we discuss an experiment using a multiple-species laminar flow reaction vessel coupled to a singlet oxygen generator. The present results suggest that all clusters react with singlet oxygen. Additionally, we observe Al 9 À , a cluster previously unidentified as having any notable stability, as being resistant to reaction with triplet oxygen. Furthermore, we discuss a means of estimating rate constants in a multiple-species flow tube where the products and reactants do not allow the use of traditional methods.
The Journal of Physical Chemistry A, 2011
The kinetics for conversion of NO(+)(H(2)O)(n) to H(3)O(+)(H(2)O)(n) has been investigated as a f... more The kinetics for conversion of NO(+)(H(2)O)(n) to H(3)O(+)(H(2)O)(n) has been investigated as a function of temperature from 150 to 400 K. In contrast to previous studies, which show that the conversion goes completely through a reaction of NO(+)(H(2)O)(3), the present results show that NO(+)(H(2)O)(4) plays an increasing role in the conversion as the temperature is lowered. Rate constants are derived for the clustering of H(2)O to NO(+)(H(2)O)(1-3) and the reactions of NO(+)(H(2)O)(3,4) with H(2)O to form H(3)O(+)(H(2)O)(2,3), respectively. In addition, thermal dissociation of NO(+)(H(2)O)(4) to lose HNO(2) was also found to be important. The rate constants for the clustering increase substantially with the lowering of the temperature. Flux calculations show that NO(+)(H(2)O)(4) accounts for over 99% of the conversion at 150 K and even 20% at 300 K, although it is too small to be detectable. The experimental data are complimented by modeling of the falloff curves for the clustering reactions. The modeling shows that, for many of the conditions, the data correspond to the falloff regime of third body association.
The Journal of Physical Chemistry A, 2010
The quenching of vibrationally excited NO + by O 2 (a 1 ∆ g) has been examined using the monitor ... more The quenching of vibrationally excited NO + by O 2 (a 1 ∆ g) has been examined using the monitor ion technique and chemical generation of O 2 (a 1 ∆ g). In contrast to previous results which showed that the rate constant was much larger than for ground state O 2 , this study finds that the rate constant for quenching is below the detection limit (<10-11 cm 3 s-1) of this experiment. The previous experiments produced O 2 (a 1 ∆ g) in a discharge, which would also produces O atoms. We found that the monitor ion CH 3 I + reacts with O atoms to produce CHIOH +. This is the likely cause of error in the previous experiments.
The Journal of Physical Chemistry A, 2010
The reactivity of O(2)(a (1)Delta(g)) was studied with a series of anions, including (-)CH(2)CN, ... more The reactivity of O(2)(a (1)Delta(g)) was studied with a series of anions, including (-)CH(2)CN, (-)CH(2)NO(2), (-)CH(2)C(O)H, CH(3)C(O)CH(2)(-), C(2)H(5)O(-), (CH(3))(2)CHO(-), CF(3)CH(2)O(-), CF(3)(-), HC(2)(-), HCCO(-), HC(O)O(-), CH(3)C(O)O(-), CH(3)OC(O)CH(2)(-), and HS(-). Reaction rate constants and product ion branching ratios were measured. All of the carbanions react through a common pathway to produce their major products. O(2)(a) adds across a bond at the site of the negative charge, resulting in the cleavage of this bond and the O=O bond. Oxyanions react through a hydride transfer to produce their major products. Proton transfer within these product ion-dipole complexes can occur, where the final branching ratios reflect the basicity of the resulting anions. Several of these anions (CF(3)(-), HC(2)(-), CH(3)OC(O)CH(2)(-)) were also found to undergo several sequential reactions within a single encounter. These three basic types of mechanisms are supported by calculations; a potential energy diagram for each type of reaction has been calculated. Additionally, six of these reactions had been qualitatively studied before; our results are in agreement with previous data.
The Journal of Physical Chemistry A, 2007
The Journal of Physical Chemistry A, 2013
The gas-phase reactions of F − (DMSO), F − (CH 3 CN), and F − (C 6 H 6) with t-butyl halides were... more The gas-phase reactions of F − (DMSO), F − (CH 3 CN), and F − (C 6 H 6) with t-butyl halides were investigated. Reaction rate constants, kinetic isotope effects, and product ion branching ratios were measured using the flowing afterglow selected ion flow tube technique (FA-SIFT). Additionally, the structure of F − (DMSO) was investigated both computationally and experimentally, and two stable isomers were identified. The reactions generally proceed by elimination mechanisms; however, the reaction of F − (C 6 H 6) with tbutyl chloride occurs by a switching mechanism. These reactions are compared to previous studies of microsolvated reactions of t-butyl halides where the solvent molecules were polar, protic molecules.
The Astrophysical Journal, 2008
Journal of the American Society for Mass Spectrometry, 2008
The gas-phase reactions of F~(CH30H) and F~(CzH50H) with t-butyl bromide have been investigated t... more The gas-phase reactions of F~(CH30H) and F~(CzH50H) with t-butyl bromide have been investigated to explore the effect of the solvent on the E2 transition state. Kinetic isotope effects (KIEs) were measured using a flowing afterglow-selected ion flow tube (FA-SIFT) mass spectrometer upon deuteration of both the alkyl halide and the alcohol. Kinetic isotope effects are significantly more pronounced than those previously observed for similar reactions of F~(HzO) with t-butyl halides. KIEs for the reaction of F~(CH30H) with t-butyl bromide are 2.10 upon deuteration of the neutral reagent and 0.74 upon deuteration of the solvent. KIEs for the reaction of F-(CzHsOH) with t-butyl bromide are 3.84 upon deuteration of the neutral reagent and 0.66 upon deuteration of the solvent. The magnitude of these effects is discussed in terms of transition-state looseness. Additionally, deuteration of the neutral regent and deuteration of the solvent do not produce completely separable isotope effects, which is likely due to a crowded transition state. These results are compared to our previous work on S N2 and E2 solvated systems.
Journal of the American Chemical Society, 2008
Journal of the American Chemical Society, 2009
Reaction rate constants and deuterium kinetic isotope effects for the reactions of BrOwith RCl (R... more Reaction rate constants and deuterium kinetic isotope effects for the reactions of BrOwith RCl (R) methyl, ethyl, isopropyl, and tert-butyl) were measured using a tandem flowing afterglow-selected ion flow tube instrument. These results provide qualitative insight into the competition between two classical organic mechanisms, nucleophilic substitution (S N 2) and base-induced elimination (E2). As the extent of substitution in the neutral reactants increases, the kinetic isotope effects become increasingly more normal, consistent with the gradual onset of the E2 channel. These results are in excellent agreement with previously reported trends for the analogous reactions of ClOwith RCl. [Villano et al. J. Am. Chem. Soc. 2006, 128, 728.] However, the reactions of BrOand ClOwith methyl chloride, ethyl chloride, and isopropyl chloride were found to occur by an additional reaction pathway, which has not previously been reported. This reaction likely proceeds initially through a traditional S N 2 transition state, followed by an elimination step in the S N 2 product ion-dipole complex. Furthermore, the controversial R-nucleophilic character of these two anions and of the HO 2 anion is examined. No enhanced reactivity is displayed. These results suggest that the R-effect is not due to an intrinsic property of the anion but instead due to a solvent effect.
Journal of the American Chemical Society, 2010
Direct comparisons of the reactivity and mechanistic pathways for anionic systems in the gas phas... more Direct comparisons of the reactivity and mechanistic pathways for anionic systems in the gas phase and in solution are presented. Rate constants and kinetic isotope effects for the reactions of methyl, ethyl, isopropyl, and tert-butyl iodide with cyanide ion in the gas phase, as well as for the reactions of methyl and ethyl iodide with cyanide ion in several solvents, are reported. In addition to measuring the perdeutero kinetic isotope effect (KIE) for each reaction, the secondary R-and-deuterium KIEs were determined for the ethyl iodide reaction. Comparisons of experimental results with computational transition states, KIEs, and branching fractions are explored to determine how solvent affects these reactions. The KIEs show that the transition state does not change significantly when the solvent is changed from dimethyl sulfoxide/methanol (a protic solvent) to dimethyl sulfoxide (a strongly polar aprotic solvent) to tetrahydrofuran (a slightly polar aprotic solvent) in the ethyl iodide-cyanide ion S N 2 reaction in solution, as the "Solvation Rule for S N 2 Reactions" predicts. However, the Solvation Rule fails the ultimate test of predicting gas phase results, where significantly smaller (more inverse) KIEs indicate the existence of a tighter transition state. This result is primarily attributed to the greater electrostatic forces between the partial negative charges on the iodide and cyanide ions and the partial positive charge on the R carbon in the gas phase transition state. Nevertheless, in evaluating the competition between S N 2 and E2 processes, the mechanistic results for the solution and gas phase reactions are strikingly similar. The reaction of cyanide ion with ethyl iodide occurs exclusively by an S N 2 mechanism in solution and primarily by an S N 2 mechanism in the gas phase; only ∼1% of the gas phase reaction is ascribed to an elimination process.
The Journal of Physical Chemistry Letters, 2011
Public reporting burden for this collection of information is estimated to average 1 hour per res... more Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.
 with OH[sup −](H[sub 2]O)[sub 1,2] clusters](https://attachments.academia-assets.com/88097808/thumbnails/1.jpg)
](The Journal of Chemical Physics, 2009
International Journal of Mass Spectrometry, 2009
... Nicole Eyet Corresponding Author Contact Information , a , E-mail The Corresponding Author , ... more ... Nicole Eyet Corresponding Author Contact Information , a , E-mail The Corresponding Author , Stephanie M. Villano a and Veronica M. Bierbaum a. ... The electron affinity must be accessible with a laser, there must be good Franck-Condon overlap between the anion and the ...
International Journal of Mass Spectrometry, 2009
The reactivities of mono-and dihalocarbene anions (CHCl •− , CHBr •− , CF 2 •− , CCl 2 •− , and C... more The reactivities of mono-and dihalocarbene anions (CHCl •− , CHBr •− , CF 2 •− , CCl 2 •− , and CBrCl •−) were studied using a tandem flowing afterglow-selected ion flow tube instrument. Reaction rate constants and product branching ratios are reported for the reactions of these carbene anions with six neutral reagents (CS 2 , COS, CO 2 , O 2 , CO, and N 2 O). These anions were found to demonstrate diverse chemistry as illustrated by formation of multiple product ions and by the observed reaction trends. The reactions of CHCl •− and CHBr •− occur with similar efficiencies and reactivity patterns. Substitution of a Cl atom for an H atom to form CCl 2 •− and CBrCl •− decreases the rate constants; these two anions react with similar efficiencies and reactivity trends. The CF 2 •− anion displays remarkably different reactivity; these differences are discussed in terms of its lower electron binding energy and the effect of the electronegative fluorine substituents. The results presented here are compared to the reactivity of the CH 2 •− anion, which has previously been reported.
International Journal of Mass Spectrometry, 2021
Abstract The temperature- and pressure-dependent kinetics of Co+(CH3Br)n (n = 0,1) + CH3Br are me... more Abstract The temperature- and pressure-dependent kinetics of Co+(CH3Br)n (n = 0,1) + CH3Br are measured from 300 to 600 K and from 0.2 to 0.5 Torr. Results are interpreted using density functional calculations and modeled with statistical theory. In the n = 0 case, the associative product Co+(CH3Br) dominates with a rate constant between 5 and 30% of the collisional value, while a minor channel yields CoBr+ + CH3 with a rate constant increasing with temperature. 0K bond dissociation energies (BDE) are determined for Co+-Br (2.8 ± 0.1 eV) and Co+-CH3Br (2.4 ± 0.25 eV). Ligation of Co+ (i.e. n = 1) significantly increases the bimolecular reaction rate constant. CoBr+(CH3Br) + CH3 is formed and the reaction has a positive temperature dependence. Interestingly, this rate constant decreases with increasing pressure due to competition of the association channel. Ligation increases the (CH3Br)Co+-Br BDE (3.0 ± 0.1 eV) relative to Co+-Br, but decreases the (CH3Br)Co+-CH3Br BDE (1.95 ± 0.25) relative to Co+-CH3Br. Both bimolecular reactions proceed by a metal-insertion mechanism with a significantly submerged transition state that does not affect the kinetics. Instead, the endothermicity of the reaction is rate-limiting. Discussion about how energy, impact parameter, and angular momentum affect specific rate constants for dissociation to reactants, reaction to products, and association are presented.
3 , probably because of the extremely explosive character of the compound. There are 4 exothermic... more 3 , probably because of the extremely explosive character of the compound. There are 4 exothermic channels in electron attachment to ClN 3 , but only the Cl − channel was observed to occur at 298 and 400 K in the present work. Electron attachment rates were measured to be 3.5 × 10 −8 and 4.5 × 10 −8 cm 3 s −1 at 298 K and 400 K, ±35%, using a FALP apparatus. The activation energy for the reaction is 24 ± 10 meV. The reactivity of ClN 3 with 17 negative ions and 21 positive ions has been investigated at 300 K using a SIFT apparatus. The electron affinity, (2.48 ± 0.20 eV), proton affinity (713 ± 41 kJ mol −1), and ionization energy (> 9.6 eV) of ClN 3 were bracketed. These measurements are in agreement with results from G3 calculations. For negative ion reactions, the major product of the reactions was Cl − , while charge transfer, N − 3
International Journal of Mass Spectrometry, 2015
The reactivity of microsolvated fluoride ions, F À (CH 3 OH) 0-2 , with methyl, ethyl, n-propyl, ... more The reactivity of microsolvated fluoride ions, F À (CH 3 OH) 0-2 , with methyl, ethyl, n-propyl, and t-butyl bromide is evaluated over a broad range of temperatures. Significant decreases in reactivity are observed as either solvation or temperature increases. Increasing solvation increases sensitivity to the reaction barrier as revealed by a larger temperature dependence. These reactions are dominated by an S N 2 mechanism for the methyl bromide reaction, while the S N 2 and E2 mechanisms compete for the reactions with ethyl and n-propyl bromide reactions. The elimination mechanism, with some association, dominates the t-butyl bromide reactions. In all cases the unsolvated bromide ion is the primary ionic product. Branching ratios are discussed in both qualitative and quantitative terms for all reactions at 300 K.
International Journal of Mass Spectrometry, 2015
The reactivity of microsolvated fluoride ions, F À (CH 3 OH) 0-2 , with methyl, ethyl, n-propyl, ... more The reactivity of microsolvated fluoride ions, F À (CH 3 OH) 0-2 , with methyl, ethyl, n-propyl, and t-butyl bromide is evaluated over a broad range of temperatures. Significant decreases in reactivity are observed as either solvation or temperature increases. Increasing solvation increases sensitivity to the reaction barrier as revealed by a larger temperature dependence. These reactions are dominated by an S N 2 mechanism for the methyl bromide reaction, while the S N 2 and E2 mechanisms compete for the reactions with ethyl and n-propyl bromide reactions. The elimination mechanism, with some association, dominates the t-butyl bromide reactions. In all cases the unsolvated bromide ion is the primary ionic product. Branching ratios are discussed in both qualitative and quantitative terms for all reactions at 300 K.
The Journal of Physical Chemistry C, 2011
Recently, it was discovered that specific aluminum clusters (e.g., Al 13 À) that demonstrate enha... more Recently, it was discovered that specific aluminum clusters (e.g., Al 13 À) that demonstrate enhanced resistance to reactivity with oxygen may do so not only because of a closed electronic jellium shell as originally supposed but also because of a forbidden spin-flip in the transition state of the reaction. Herein, we discuss an experiment using a multiple-species laminar flow reaction vessel coupled to a singlet oxygen generator. The present results suggest that all clusters react with singlet oxygen. Additionally, we observe Al 9 À , a cluster previously unidentified as having any notable stability, as being resistant to reaction with triplet oxygen. Furthermore, we discuss a means of estimating rate constants in a multiple-species flow tube where the products and reactants do not allow the use of traditional methods.
The Journal of Physical Chemistry A, 2011
The kinetics for conversion of NO(+)(H(2)O)(n) to H(3)O(+)(H(2)O)(n) has been investigated as a f... more The kinetics for conversion of NO(+)(H(2)O)(n) to H(3)O(+)(H(2)O)(n) has been investigated as a function of temperature from 150 to 400 K. In contrast to previous studies, which show that the conversion goes completely through a reaction of NO(+)(H(2)O)(3), the present results show that NO(+)(H(2)O)(4) plays an increasing role in the conversion as the temperature is lowered. Rate constants are derived for the clustering of H(2)O to NO(+)(H(2)O)(1-3) and the reactions of NO(+)(H(2)O)(3,4) with H(2)O to form H(3)O(+)(H(2)O)(2,3), respectively. In addition, thermal dissociation of NO(+)(H(2)O)(4) to lose HNO(2) was also found to be important. The rate constants for the clustering increase substantially with the lowering of the temperature. Flux calculations show that NO(+)(H(2)O)(4) accounts for over 99% of the conversion at 150 K and even 20% at 300 K, although it is too small to be detectable. The experimental data are complimented by modeling of the falloff curves for the clustering reactions. The modeling shows that, for many of the conditions, the data correspond to the falloff regime of third body association.
The Journal of Physical Chemistry A, 2010
The quenching of vibrationally excited NO + by O 2 (a 1 ∆ g) has been examined using the monitor ... more The quenching of vibrationally excited NO + by O 2 (a 1 ∆ g) has been examined using the monitor ion technique and chemical generation of O 2 (a 1 ∆ g). In contrast to previous results which showed that the rate constant was much larger than for ground state O 2 , this study finds that the rate constant for quenching is below the detection limit (<10-11 cm 3 s-1) of this experiment. The previous experiments produced O 2 (a 1 ∆ g) in a discharge, which would also produces O atoms. We found that the monitor ion CH 3 I + reacts with O atoms to produce CHIOH +. This is the likely cause of error in the previous experiments.
The Journal of Physical Chemistry A, 2010
The reactivity of O(2)(a (1)Delta(g)) was studied with a series of anions, including (-)CH(2)CN, ... more The reactivity of O(2)(a (1)Delta(g)) was studied with a series of anions, including (-)CH(2)CN, (-)CH(2)NO(2), (-)CH(2)C(O)H, CH(3)C(O)CH(2)(-), C(2)H(5)O(-), (CH(3))(2)CHO(-), CF(3)CH(2)O(-), CF(3)(-), HC(2)(-), HCCO(-), HC(O)O(-), CH(3)C(O)O(-), CH(3)OC(O)CH(2)(-), and HS(-). Reaction rate constants and product ion branching ratios were measured. All of the carbanions react through a common pathway to produce their major products. O(2)(a) adds across a bond at the site of the negative charge, resulting in the cleavage of this bond and the O=O bond. Oxyanions react through a hydride transfer to produce their major products. Proton transfer within these product ion-dipole complexes can occur, where the final branching ratios reflect the basicity of the resulting anions. Several of these anions (CF(3)(-), HC(2)(-), CH(3)OC(O)CH(2)(-)) were also found to undergo several sequential reactions within a single encounter. These three basic types of mechanisms are supported by calculations; a potential energy diagram for each type of reaction has been calculated. Additionally, six of these reactions had been qualitatively studied before; our results are in agreement with previous data.
The Journal of Physical Chemistry A, 2007
The Journal of Physical Chemistry A, 2013
The gas-phase reactions of F − (DMSO), F − (CH 3 CN), and F − (C 6 H 6) with t-butyl halides were... more The gas-phase reactions of F − (DMSO), F − (CH 3 CN), and F − (C 6 H 6) with t-butyl halides were investigated. Reaction rate constants, kinetic isotope effects, and product ion branching ratios were measured using the flowing afterglow selected ion flow tube technique (FA-SIFT). Additionally, the structure of F − (DMSO) was investigated both computationally and experimentally, and two stable isomers were identified. The reactions generally proceed by elimination mechanisms; however, the reaction of F − (C 6 H 6) with tbutyl chloride occurs by a switching mechanism. These reactions are compared to previous studies of microsolvated reactions of t-butyl halides where the solvent molecules were polar, protic molecules.
The Astrophysical Journal, 2008
Journal of the American Society for Mass Spectrometry, 2008
The gas-phase reactions of F~(CH30H) and F~(CzH50H) with t-butyl bromide have been investigated t... more The gas-phase reactions of F~(CH30H) and F~(CzH50H) with t-butyl bromide have been investigated to explore the effect of the solvent on the E2 transition state. Kinetic isotope effects (KIEs) were measured using a flowing afterglow-selected ion flow tube (FA-SIFT) mass spectrometer upon deuteration of both the alkyl halide and the alcohol. Kinetic isotope effects are significantly more pronounced than those previously observed for similar reactions of F~(HzO) with t-butyl halides. KIEs for the reaction of F~(CH30H) with t-butyl bromide are 2.10 upon deuteration of the neutral reagent and 0.74 upon deuteration of the solvent. KIEs for the reaction of F-(CzHsOH) with t-butyl bromide are 3.84 upon deuteration of the neutral reagent and 0.66 upon deuteration of the solvent. The magnitude of these effects is discussed in terms of transition-state looseness. Additionally, deuteration of the neutral regent and deuteration of the solvent do not produce completely separable isotope effects, which is likely due to a crowded transition state. These results are compared to our previous work on S N2 and E2 solvated systems.
Journal of the American Chemical Society, 2008
Journal of the American Chemical Society, 2009
Reaction rate constants and deuterium kinetic isotope effects for the reactions of BrOwith RCl (R... more Reaction rate constants and deuterium kinetic isotope effects for the reactions of BrOwith RCl (R) methyl, ethyl, isopropyl, and tert-butyl) were measured using a tandem flowing afterglow-selected ion flow tube instrument. These results provide qualitative insight into the competition between two classical organic mechanisms, nucleophilic substitution (S N 2) and base-induced elimination (E2). As the extent of substitution in the neutral reactants increases, the kinetic isotope effects become increasingly more normal, consistent with the gradual onset of the E2 channel. These results are in excellent agreement with previously reported trends for the analogous reactions of ClOwith RCl. [Villano et al. J. Am. Chem. Soc. 2006, 128, 728.] However, the reactions of BrOand ClOwith methyl chloride, ethyl chloride, and isopropyl chloride were found to occur by an additional reaction pathway, which has not previously been reported. This reaction likely proceeds initially through a traditional S N 2 transition state, followed by an elimination step in the S N 2 product ion-dipole complex. Furthermore, the controversial R-nucleophilic character of these two anions and of the HO 2 anion is examined. No enhanced reactivity is displayed. These results suggest that the R-effect is not due to an intrinsic property of the anion but instead due to a solvent effect.
Journal of the American Chemical Society, 2010
Direct comparisons of the reactivity and mechanistic pathways for anionic systems in the gas phas... more Direct comparisons of the reactivity and mechanistic pathways for anionic systems in the gas phase and in solution are presented. Rate constants and kinetic isotope effects for the reactions of methyl, ethyl, isopropyl, and tert-butyl iodide with cyanide ion in the gas phase, as well as for the reactions of methyl and ethyl iodide with cyanide ion in several solvents, are reported. In addition to measuring the perdeutero kinetic isotope effect (KIE) for each reaction, the secondary R-and-deuterium KIEs were determined for the ethyl iodide reaction. Comparisons of experimental results with computational transition states, KIEs, and branching fractions are explored to determine how solvent affects these reactions. The KIEs show that the transition state does not change significantly when the solvent is changed from dimethyl sulfoxide/methanol (a protic solvent) to dimethyl sulfoxide (a strongly polar aprotic solvent) to tetrahydrofuran (a slightly polar aprotic solvent) in the ethyl iodide-cyanide ion S N 2 reaction in solution, as the "Solvation Rule for S N 2 Reactions" predicts. However, the Solvation Rule fails the ultimate test of predicting gas phase results, where significantly smaller (more inverse) KIEs indicate the existence of a tighter transition state. This result is primarily attributed to the greater electrostatic forces between the partial negative charges on the iodide and cyanide ions and the partial positive charge on the R carbon in the gas phase transition state. Nevertheless, in evaluating the competition between S N 2 and E2 processes, the mechanistic results for the solution and gas phase reactions are strikingly similar. The reaction of cyanide ion with ethyl iodide occurs exclusively by an S N 2 mechanism in solution and primarily by an S N 2 mechanism in the gas phase; only ∼1% of the gas phase reaction is ascribed to an elimination process.
The Journal of Physical Chemistry Letters, 2011
Public reporting burden for this collection of information is estimated to average 1 hour per res... more Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.
The Journal of Chemical Physics, 2009
International Journal of Mass Spectrometry, 2009
... Nicole Eyet Corresponding Author Contact Information , a , E-mail The Corresponding Author , ... more ... Nicole Eyet Corresponding Author Contact Information , a , E-mail The Corresponding Author , Stephanie M. Villano a and Veronica M. Bierbaum a. ... The electron affinity must be accessible with a laser, there must be good Franck-Condon overlap between the anion and the ...
International Journal of Mass Spectrometry, 2009
The reactivities of mono-and dihalocarbene anions (CHCl •− , CHBr •− , CF 2 •− , CCl 2 •− , and C... more The reactivities of mono-and dihalocarbene anions (CHCl •− , CHBr •− , CF 2 •− , CCl 2 •− , and CBrCl •−) were studied using a tandem flowing afterglow-selected ion flow tube instrument. Reaction rate constants and product branching ratios are reported for the reactions of these carbene anions with six neutral reagents (CS 2 , COS, CO 2 , O 2 , CO, and N 2 O). These anions were found to demonstrate diverse chemistry as illustrated by formation of multiple product ions and by the observed reaction trends. The reactions of CHCl •− and CHBr •− occur with similar efficiencies and reactivity patterns. Substitution of a Cl atom for an H atom to form CCl 2 •− and CBrCl •− decreases the rate constants; these two anions react with similar efficiencies and reactivity trends. The CF 2 •− anion displays remarkably different reactivity; these differences are discussed in terms of its lower electron binding energy and the effect of the electronegative fluorine substituents. The results presented here are compared to the reactivity of the CH 2 •− anion, which has previously been reported.