Jennifer Reece - Academia.edu (original) (raw)
Papers by Jennifer Reece
The reactivities of three isomeric, charged ortho-pyridynes, the 1,2-, 2,3-, and 3,4-didehydropyr... more The reactivities of three isomeric, charged ortho-pyridynes, the 1,2-, 2,3-, and 3,4-didehydropyridinium cations, were examined in the gas phase using Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry. The structures of selected product ions were probed using collision-activated dissociation (CAD) experiments in a linear quadrupole ion trap (LQIT) mass spectrometer. Mechanisms based on quantum chemical calculations are proposed for the formation of all major products. The products of the reactions of the charged ortho-pyridynes in the gas phase were found to closely resemble those formed upon reactions of neutral ortho-arynes in solution, but the mechanisms of these reactions exhibit striking differences. Additionally, no radical reactions were observed for any of the charged ortho-pyridynes examined, in contrast to previous proposals that ortho-benzyne can occasionally react via radical mechanisms. Finally, the relative reactivities of those charged gaseous ortho-pyridynes that yielded similar product distributions were found to be affected mainly by the (calculated) vertical electron affinities of the dehydrocarbon sites, which suggests that the reactivity of these species is controlled by polar effects.
Phenyl mono- and biradicals play important roles, for example, in organic synthesis and in the bi... more Phenyl mono- and biradicals play important roles, for example, in organic synthesis and in the biological activity of certain drugs. The presence of unpaired electrons lends these species unique chemical properties. Many parameters may be involved in controlling their reactivity. A better understanding of these parameters may lead to the ability to alter, or tune, the reactivity of radical species, which would be highly desirable. Therefore, studies leading to an improved understanding of these reactive intermediates are needed. While the chemical properties of many pyridine-based σ-type mono-, bi- and triradicals have been studied, the behavior of pyridine-based tetraradicals is still unknown. There are also many aspects of the effects of substituents on radical reactivity that remain unclear. This thesis describes the generation of a pyridine-based σ,σ,σ,σ-tetraradical, as well as studies on the effects of the hydroxy substituent on the reactivity of σ-monoradicals. Fourier transf...
Recent studies have shown that the reactivity of the 4-dehydropyridinium cation significantly dif... more Recent studies have shown that the reactivity of the 4-dehydropyridinium cation significantly differs from the reactivities of its isomers toward tetrahydrofuran. While only hydrogen atom abstraction was observed for the 2-and 3-dehydropyridinium cations, nonradical reactions were observed for the 4-isomer. In order to learn more about these reactions, the gas-phase reactivities of the 4-dehydropyridinium cation and several of its derivatives toward tetrahydrofuran were investigated in a Fourier transform ion electron resonance mass spectrometer. Both radical and nonradical reactions were observed for most of these positively charged radicals. The major parameter determining whether nonradical reactions occur was found to be the electron affinity of the radicalsonly those with relatively high electron affinities underwent nonradical reactions. The reactivities of the monoradicals are also affected by hydrogen bonding and steric effects.
Chemical Science, 2014
The reactivities of eleven 3,5-didehydropyridinium and six 2,4-didehydropyridinium cations toward... more The reactivities of eleven 3,5-didehydropyridinium and six 2,4-didehydropyridinium cations toward cyclohexane were examined in the gas phase by using Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry as well as high-level quantum chemical calculations. The results unequivocally demonstrate that the reactivity of meta-benzyne analogs can be "tuned" from more radical-like to less radical-like by changing the type and position of substituents. For example, s-acceptor substituents at the 4-position and p-donor substituents at the 2-position in 3,5didehydropyridinium cations partially decouple the biradical electrons, which results in lower energy transition states, and faster radical reactions. In contrast, s-acceptors at the 2-position and p-donors at the 4-position in 3,5-didehydropyridinium cations cause stronger coupling between the biradical electrons, which results in lower radical reactivity. Three main factors are found to control the reactivity of these biradicals: (1) the energy required to distort the minimum energy dehydrocarbon atom separation to the separation of the transition state, (2) the S-T splitting at the separation of the transition state, and (3) the electron affinity at the separation of the transition state.
The Journal of Physical Chemistry A, 2013
The α-effect, an enhanced reactivity of nucleophiles with a lone-pair adjacent to the reaction ce... more The α-effect, an enhanced reactivity of nucleophiles with a lone-pair adjacent to the reaction center, has been studied in solution for several decades. The gasphase α-effect has recently been documented in studies of S N 2 reactions as well as in competing reactions for both bare and microhydrated anions. In the present work we extend our studies of the significance of microsolvation on the α-effect, employing methanol as the solvent, in the expectation that the greater stability of the methanol cluster relative to the water cluster will lower the reactivity and thereby allow studies over a wider efficiency range. We compare the gas-phase reactivity of the microsolvated αnucleophile HOO − (CH 3 OH) to that of microsolvated normal alkoxy nucleophiles, RO − (CH 3 OH) in reactions with CH 3 Cl and CH 3 Br. The results reveal enhanced reactivity of HOO − (CH 3 OH) toward both methyl halides relative to the normal nucleophiles, and clearly demonstrate the presence of an α-effect for the microsolvated α-nucleophile. The highly exothermic reactions with methyl bromide result in a smaller Brønsted β nuc value than observed for methyl chloride, and the α-effect in turn influences the reactions with methyl chloride more than with methyl bromide. Computational investigations reveal that reactions with methyl bromide proceed through earlier transition states with less advanced bond formation compared to the related reactions of methyl chloride. In addition, solvent interactions for HOO − are quite different from those with the normal nucleophiles at the transition state, indicating that differential solvation may well contribute to the α-effect. The greater thermodynamic and kinetic stability of the anion-methanol clusters relative to the anion-water clusters accounts well for the differences in the influence of solvation with the two protic polar solvents.
The Journal of Physical Chemistry A, 2012
Recent studies have shown that the reactivity of the 4-dehydropyridinium cation significantly dif... more Recent studies have shown that the reactivity of the 4-dehydropyridinium cation significantly differs from the reactivities of its isomers toward tetrahydrofuran. While only hydrogen atom abstraction was observed for the 2-and 3-dehydropyridinium cations, nonradical reactions were observed for the 4-isomer. In order to learn more about these reactions, the gas-phase reactivities of the 4-dehydropyridinium cation and several of its derivatives toward tetrahydrofuran were investigated in a Fourier transform ion electron resonance mass spectrometer. Both radical and nonradical reactions were observed for most of these positively charged radicals. The major parameter determining whether nonradical reactions occur was found to be the electron affinity of the radicalsonly those with relatively high electron affinities underwent nonradical reactions. The reactivities of the monoradicals are also affected by hydrogen bonding and steric effects.
Journal of The American Society for Mass Spectrometry, 2014
The enhanced reactivity of α-nucleophiles, which contain an electron lone pair adjacent to the re... more The enhanced reactivity of α-nucleophiles, which contain an electron lone pair adjacent to the reactive site, has been demonstrated in solution and in the gas phase and, recently, for the gas-phase S N 2 reactions of the microsolvated HOO -(H 2 O) ion with methyl chloride. In the present work, we continue to explore the significance of microsolvation on the α-effect as we compare the gas-phase reactivity of the microsolvated α-nucleophile HOO -(H2O) with that of microsolvated normal alkoxy nucleophiles, RO -(H2O), in reactions with methyl formate, where three competing reactions are possible. The results reveal enhanced reactivity of HOO -(H 2 O) towards methyl formate, and clearly demonstrate the presence of an overall α-effect for the reactions of the microsolvated αnucleophile. The association of the nucleophiles with a single water molecule significantly lowers the degree of proton abstraction and increases the S N 2 and B AC 2 reactivity compared with the unsolvated analogs. HOO -(H 2 O) reacts with methyl formate exclusively via the B AC 2 channel. While microsolvation lowers the overall reaction efficiency, it enhances the BAC2 reaction efficiency for all anions compared with the unsolvated analogs. This may be explained by participation of the solvent water molecule in the BAC2 reaction in a way that continuously stabilizes the negative charge throughout the reaction.
Journal of the American Chemical Society, 2013
The α-effect-enhanced reactivity of nucleophiles with a lone-pair adjacent to the attacking cente... more The α-effect-enhanced reactivity of nucleophiles with a lone-pair adjacent to the attacking center-was recently demonstrated for gas-phase S(N)2 reactions of HOO(-), supporting an intrinsic component of the α-effect. In the present work we explore the gas-phase reactivity of microsolvated nucleophiles in order to investigate in detail how the α-effect is influenced by solvent. We compare the gas-phase reactivity of the microsolvated α-nucleophile HOO(-)(H2O) to that of microsolvated normal alkoxy nucleophiles, RO(-)(H2O), in reaction with CH3Cl using a flowing afterglow-selected ion flow tube instrument. The results reveal enhanced reactivity of HOO(-)(H2O) and clearly demonstrate the presence of an α-effect for the microsolvated α-nucleophile. The association of the nucleophile with a single water molecule results in a larger Brønsted βnuc value than is the case for the unsolvated nucleophiles. Accordingly, the reactions of the microsolvated nucleophiles proceed through later transition states in which bond formation has progressed further. Calculations show a significant difference in solvent interaction for HOO(-) relative to the normal nucleophiles at the transition states, indicating that differential solvation may well contribute to the α-effect. The reactions of the microsolvated anions with CH3Cl can lead to formation of either the bare Cl(-) anion or the Cl(-)(H2O) cluster. The product distributions show preferential formation of the Cl(-) anion even though the formation of Cl(-)(H2O) would be favored thermodynamically. Although the structure of the HOO(-)(H2O) cluster resembles HO(-)(HOOH), we demonstrate that HOO(-) is the active nucleophile when the cluster reacts.
Energy & Fuels, 2012
ABSTRACT
Chemistry - A European Journal, 2012
. Resonance structures of 2,4,6-tridehydropyridinium ion 7.
Analytical Chemistry, 2012
Over the years, ultrahigh resolution mass spectrometry has successfully illustrated the extreme c... more Over the years, ultrahigh resolution mass spectrometry has successfully illustrated the extreme complexity of crude oil and related solubility or polarity based fractions on a molecular level. However, the applied ionization technique greatly influences the outcome and may provide misleading information. In this work, we investigate the atmospheric pressure laser ionization (APLI) technique coupled with Fourier transform ion cyclotron resonance mass spectrometer to analyze the asphaltene fraction of a crude oil. These results were compared to data obtained by using other existing atmospheric pressure ionization methods. Furthermore elemental analysis and solid state NMR were used to obtain the bulk characteristics of the asphaltene sample. The results of the different ionization techniques were compared with the bulk properties in order to describe the potential discrimination effects of the ionization techniques that were observed. The results showed that APLI expands the range of the assigned molecules, while retaining information already observed with the generally used ion sources.
Phenyl mono- and biradicals play important roles, for example, in organic synthesis and in the bi... more Phenyl mono- and biradicals play important roles, for example, in organic synthesis and in the biological activity of certain drugs. The presence of unpaired electrons lends these species unique chemical properties. Many parameters may be involved in controlling their reactivity. A better understanding of these parameters may lead to the ability to alter, or tune, the reactivity of radical species, which would be highly desirable. Therefore, studies leading to an improved understanding of these reactive intermediates are needed. While the chemical properties of many pyridine-based σ-type mono-, bi- and triradicals have been studied, the behavior of pyridine-based tetraradicals is still unknown. There are also many aspects of the effects of substituents on radical reactivity that remain unclear. This thesis describes the generation of a pyridine-based σ,σ,σ,σ-tetraradical, as well as studies on the effects of the hydroxy substituent on the reactivity of σ-monoradicals. Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry was employed for these studies.^ In addition to aiding fundamental studies, as described above, mass spectrometry is also an extremely valuble tool in the field of mixture analysis and structural elucidation of unknown compounds. Especially, tandem mass spectrometry (MS/MS) coupled with collision-activated dissociation (CAD) provides a wealth of structural information for unknown analytes directly in mixtures. In this thesis, a linear quadrupole ion trap (LQIT) mass spectrometer coupled with high-performance liquid chromatography (HPLC) was demonstrated to allow detailed structural characterization of unknown organic compounds in mixtures.^
… . Chem. Int. Ed, Jan 1, 2008
The reactivities of three isomeric, charged ortho-pyridynes, the 1,2-, 2,3-, and 3,4-didehydropyr... more The reactivities of three isomeric, charged ortho-pyridynes, the 1,2-, 2,3-, and 3,4-didehydropyridinium cations, were examined in the gas phase using Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry. The structures of selected product ions were probed using collision-activated dissociation (CAD) experiments in a linear quadrupole ion trap (LQIT) mass spectrometer. Mechanisms based on quantum chemical calculations are proposed for the formation of all major products. The products of the reactions of the charged ortho-pyridynes in the gas phase were found to closely resemble those formed upon reactions of neutral ortho-arynes in solution, but the mechanisms of these reactions exhibit striking differences. Additionally, no radical reactions were observed for any of the charged ortho-pyridynes examined, in contrast to previous proposals that ortho-benzyne can occasionally react via radical mechanisms. Finally, the relative reactivities of those charged gaseous ortho-pyridynes that yielded similar product distributions were found to be affected mainly by the (calculated) vertical electron affinities of the dehydrocarbon sites, which suggests that the reactivity of these species is controlled by polar effects.
Phenyl mono- and biradicals play important roles, for example, in organic synthesis and in the bi... more Phenyl mono- and biradicals play important roles, for example, in organic synthesis and in the biological activity of certain drugs. The presence of unpaired electrons lends these species unique chemical properties. Many parameters may be involved in controlling their reactivity. A better understanding of these parameters may lead to the ability to alter, or tune, the reactivity of radical species, which would be highly desirable. Therefore, studies leading to an improved understanding of these reactive intermediates are needed. While the chemical properties of many pyridine-based σ-type mono-, bi- and triradicals have been studied, the behavior of pyridine-based tetraradicals is still unknown. There are also many aspects of the effects of substituents on radical reactivity that remain unclear. This thesis describes the generation of a pyridine-based σ,σ,σ,σ-tetraradical, as well as studies on the effects of the hydroxy substituent on the reactivity of σ-monoradicals. Fourier transf...
Recent studies have shown that the reactivity of the 4-dehydropyridinium cation significantly dif... more Recent studies have shown that the reactivity of the 4-dehydropyridinium cation significantly differs from the reactivities of its isomers toward tetrahydrofuran. While only hydrogen atom abstraction was observed for the 2-and 3-dehydropyridinium cations, nonradical reactions were observed for the 4-isomer. In order to learn more about these reactions, the gas-phase reactivities of the 4-dehydropyridinium cation and several of its derivatives toward tetrahydrofuran were investigated in a Fourier transform ion electron resonance mass spectrometer. Both radical and nonradical reactions were observed for most of these positively charged radicals. The major parameter determining whether nonradical reactions occur was found to be the electron affinity of the radicalsonly those with relatively high electron affinities underwent nonradical reactions. The reactivities of the monoradicals are also affected by hydrogen bonding and steric effects.
Chemical Science, 2014
The reactivities of eleven 3,5-didehydropyridinium and six 2,4-didehydropyridinium cations toward... more The reactivities of eleven 3,5-didehydropyridinium and six 2,4-didehydropyridinium cations toward cyclohexane were examined in the gas phase by using Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry as well as high-level quantum chemical calculations. The results unequivocally demonstrate that the reactivity of meta-benzyne analogs can be "tuned" from more radical-like to less radical-like by changing the type and position of substituents. For example, s-acceptor substituents at the 4-position and p-donor substituents at the 2-position in 3,5didehydropyridinium cations partially decouple the biradical electrons, which results in lower energy transition states, and faster radical reactions. In contrast, s-acceptors at the 2-position and p-donors at the 4-position in 3,5-didehydropyridinium cations cause stronger coupling between the biradical electrons, which results in lower radical reactivity. Three main factors are found to control the reactivity of these biradicals: (1) the energy required to distort the minimum energy dehydrocarbon atom separation to the separation of the transition state, (2) the S-T splitting at the separation of the transition state, and (3) the electron affinity at the separation of the transition state.
The Journal of Physical Chemistry A, 2013
The α-effect, an enhanced reactivity of nucleophiles with a lone-pair adjacent to the reaction ce... more The α-effect, an enhanced reactivity of nucleophiles with a lone-pair adjacent to the reaction center, has been studied in solution for several decades. The gasphase α-effect has recently been documented in studies of S N 2 reactions as well as in competing reactions for both bare and microhydrated anions. In the present work we extend our studies of the significance of microsolvation on the α-effect, employing methanol as the solvent, in the expectation that the greater stability of the methanol cluster relative to the water cluster will lower the reactivity and thereby allow studies over a wider efficiency range. We compare the gas-phase reactivity of the microsolvated αnucleophile HOO − (CH 3 OH) to that of microsolvated normal alkoxy nucleophiles, RO − (CH 3 OH) in reactions with CH 3 Cl and CH 3 Br. The results reveal enhanced reactivity of HOO − (CH 3 OH) toward both methyl halides relative to the normal nucleophiles, and clearly demonstrate the presence of an α-effect for the microsolvated α-nucleophile. The highly exothermic reactions with methyl bromide result in a smaller Brønsted β nuc value than observed for methyl chloride, and the α-effect in turn influences the reactions with methyl chloride more than with methyl bromide. Computational investigations reveal that reactions with methyl bromide proceed through earlier transition states with less advanced bond formation compared to the related reactions of methyl chloride. In addition, solvent interactions for HOO − are quite different from those with the normal nucleophiles at the transition state, indicating that differential solvation may well contribute to the α-effect. The greater thermodynamic and kinetic stability of the anion-methanol clusters relative to the anion-water clusters accounts well for the differences in the influence of solvation with the two protic polar solvents.
The Journal of Physical Chemistry A, 2012
Recent studies have shown that the reactivity of the 4-dehydropyridinium cation significantly dif... more Recent studies have shown that the reactivity of the 4-dehydropyridinium cation significantly differs from the reactivities of its isomers toward tetrahydrofuran. While only hydrogen atom abstraction was observed for the 2-and 3-dehydropyridinium cations, nonradical reactions were observed for the 4-isomer. In order to learn more about these reactions, the gas-phase reactivities of the 4-dehydropyridinium cation and several of its derivatives toward tetrahydrofuran were investigated in a Fourier transform ion electron resonance mass spectrometer. Both radical and nonradical reactions were observed for most of these positively charged radicals. The major parameter determining whether nonradical reactions occur was found to be the electron affinity of the radicalsonly those with relatively high electron affinities underwent nonradical reactions. The reactivities of the monoradicals are also affected by hydrogen bonding and steric effects.
Journal of The American Society for Mass Spectrometry, 2014
The enhanced reactivity of α-nucleophiles, which contain an electron lone pair adjacent to the re... more The enhanced reactivity of α-nucleophiles, which contain an electron lone pair adjacent to the reactive site, has been demonstrated in solution and in the gas phase and, recently, for the gas-phase S N 2 reactions of the microsolvated HOO -(H 2 O) ion with methyl chloride. In the present work, we continue to explore the significance of microsolvation on the α-effect as we compare the gas-phase reactivity of the microsolvated α-nucleophile HOO -(H2O) with that of microsolvated normal alkoxy nucleophiles, RO -(H2O), in reactions with methyl formate, where three competing reactions are possible. The results reveal enhanced reactivity of HOO -(H 2 O) towards methyl formate, and clearly demonstrate the presence of an overall α-effect for the reactions of the microsolvated αnucleophile. The association of the nucleophiles with a single water molecule significantly lowers the degree of proton abstraction and increases the S N 2 and B AC 2 reactivity compared with the unsolvated analogs. HOO -(H 2 O) reacts with methyl formate exclusively via the B AC 2 channel. While microsolvation lowers the overall reaction efficiency, it enhances the BAC2 reaction efficiency for all anions compared with the unsolvated analogs. This may be explained by participation of the solvent water molecule in the BAC2 reaction in a way that continuously stabilizes the negative charge throughout the reaction.
Journal of the American Chemical Society, 2013
The α-effect-enhanced reactivity of nucleophiles with a lone-pair adjacent to the attacking cente... more The α-effect-enhanced reactivity of nucleophiles with a lone-pair adjacent to the attacking center-was recently demonstrated for gas-phase S(N)2 reactions of HOO(-), supporting an intrinsic component of the α-effect. In the present work we explore the gas-phase reactivity of microsolvated nucleophiles in order to investigate in detail how the α-effect is influenced by solvent. We compare the gas-phase reactivity of the microsolvated α-nucleophile HOO(-)(H2O) to that of microsolvated normal alkoxy nucleophiles, RO(-)(H2O), in reaction with CH3Cl using a flowing afterglow-selected ion flow tube instrument. The results reveal enhanced reactivity of HOO(-)(H2O) and clearly demonstrate the presence of an α-effect for the microsolvated α-nucleophile. The association of the nucleophile with a single water molecule results in a larger Brønsted βnuc value than is the case for the unsolvated nucleophiles. Accordingly, the reactions of the microsolvated nucleophiles proceed through later transition states in which bond formation has progressed further. Calculations show a significant difference in solvent interaction for HOO(-) relative to the normal nucleophiles at the transition states, indicating that differential solvation may well contribute to the α-effect. The reactions of the microsolvated anions with CH3Cl can lead to formation of either the bare Cl(-) anion or the Cl(-)(H2O) cluster. The product distributions show preferential formation of the Cl(-) anion even though the formation of Cl(-)(H2O) would be favored thermodynamically. Although the structure of the HOO(-)(H2O) cluster resembles HO(-)(HOOH), we demonstrate that HOO(-) is the active nucleophile when the cluster reacts.
Energy & Fuels, 2012
ABSTRACT
Chemistry - A European Journal, 2012
. Resonance structures of 2,4,6-tridehydropyridinium ion 7.
Analytical Chemistry, 2012
Over the years, ultrahigh resolution mass spectrometry has successfully illustrated the extreme c... more Over the years, ultrahigh resolution mass spectrometry has successfully illustrated the extreme complexity of crude oil and related solubility or polarity based fractions on a molecular level. However, the applied ionization technique greatly influences the outcome and may provide misleading information. In this work, we investigate the atmospheric pressure laser ionization (APLI) technique coupled with Fourier transform ion cyclotron resonance mass spectrometer to analyze the asphaltene fraction of a crude oil. These results were compared to data obtained by using other existing atmospheric pressure ionization methods. Furthermore elemental analysis and solid state NMR were used to obtain the bulk characteristics of the asphaltene sample. The results of the different ionization techniques were compared with the bulk properties in order to describe the potential discrimination effects of the ionization techniques that were observed. The results showed that APLI expands the range of the assigned molecules, while retaining information already observed with the generally used ion sources.
Phenyl mono- and biradicals play important roles, for example, in organic synthesis and in the bi... more Phenyl mono- and biradicals play important roles, for example, in organic synthesis and in the biological activity of certain drugs. The presence of unpaired electrons lends these species unique chemical properties. Many parameters may be involved in controlling their reactivity. A better understanding of these parameters may lead to the ability to alter, or tune, the reactivity of radical species, which would be highly desirable. Therefore, studies leading to an improved understanding of these reactive intermediates are needed. While the chemical properties of many pyridine-based σ-type mono-, bi- and triradicals have been studied, the behavior of pyridine-based tetraradicals is still unknown. There are also many aspects of the effects of substituents on radical reactivity that remain unclear. This thesis describes the generation of a pyridine-based σ,σ,σ,σ-tetraradical, as well as studies on the effects of the hydroxy substituent on the reactivity of σ-monoradicals. Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry was employed for these studies.^ In addition to aiding fundamental studies, as described above, mass spectrometry is also an extremely valuble tool in the field of mixture analysis and structural elucidation of unknown compounds. Especially, tandem mass spectrometry (MS/MS) coupled with collision-activated dissociation (CAD) provides a wealth of structural information for unknown analytes directly in mixtures. In this thesis, a linear quadrupole ion trap (LQIT) mass spectrometer coupled with high-performance liquid chromatography (HPLC) was demonstrated to allow detailed structural characterization of unknown organic compounds in mixtures.^
… . Chem. Int. Ed, Jan 1, 2008