The α-effect in elimination reactions and competing mechanisms in the gas phase

Garver, John M.; Yang, Zhibo; Wehres, Nadine; Nichols, Charles M.; Worker, Benjamin B.; Bierbaum, Veronica M.

doi:10.1016/j.ijms.2012.07.016

Cited by 15 publications

(9 citation statements)

References 66 publications

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“…Our results indicate that the α‐effect does exist in gas‐phase reactions and suggest that α‐effect is measured by the downward deviation from the plot of overall enthalpy of activation, Δ H ≠ ovr , with respect to separated reactants vs. proton affinity (PA) of n ‐Nu (or base). Some recent studies have validated our prediction . For example, the gas‐phase experiments of Garver et al show the enhanced nucleophilicity for α‐Nu, HOO − , relative to the normal Nus (HO − , CH 3 O − , C 2 H 5 O − , and i ‐C 3 H 7 O) in three separate reaction series (CH 3 F, CH 3 OC 6 H 5 , and CH 3 OC 6 H 4 F), supporting an underlying intrinsic origin of the α‐effect …”

Section: Introductionsupporting

confidence: 79%

“…It was found that three anions, HOO − , MeOO − , and N 3 − each with an adjacent electron donating group, react particularly fast. The α‐effect has been studied for more than 50 years by experimental and theoretical chemists, and its origin has been rationalized by many theories, but still without a definitive answer. Theories that have been put forward for this effect include: (1) transition state (TS) stabilization, (2) destabilization of the ground state, (3) different solvent effects for normal and α‐Nu, and (4) thermodynamic stability of the product .…”

Section: Introductionmentioning

confidence: 99%

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The α-effect exhibited in gas-phase S_N2@N and S_N2@C reactions

et al. 2013

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In order to explore the existence of α-effect in gas-phase S(N)2@N reactions, and to compare its similarity and difference with its counterpart in S(N)2@C reactions, we have carried out a theoretical study on the reactivity of six α-oxy-Nus (FO(-), ClO(-), BrO(-), HOO(-), HSO(-), H2NO(-)) in the S(N)2 reactions toward NR2Cl (R = H, Me) and RCl (R = Me, i-Pr) using the G2(+)M theory. An enhanced reactivity induced by the α-atom is found in all examined systems. The magnitude of the α-effect in the reactions of NR2Cl (R = H, Me) is generally smaller than that in the corresponding S(N)2 reaction, but their variation trend with the identity of α-atom is very similar. The origin of the α-effect of the S(N)2@N reactions is discussed in terms of activation strain analysis and thermodynamic analysis, indicating that the α-effect in the S(N)2@N reactions largely arises from transition state stabilization, and the "hyper-reactivity" of these α-Nus is also accompanied by an enhanced thermodynamic stability of products from the n(N) → σ*(O-Y) negative hyperconjugation. Meanwhile, it is found that the reactivity of oxy-Nus in the S(N)2 reactions toward NMe2Cl is lower than toward i-PrCl, which is different from previous experiments, that is, the S(N)2 reactions of NH2Cl is more facile than MeCl.

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Section: Introductionsupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

The α-effect exhibited in gas-phase S_N2@N and S_N2@C reactions

et al. 2013

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“…Recently, the presence of an intrinsic component of the α-effect in S N 2 reactions was demonstrated by comparing the gas-phase reactivity of HOO − to that of the normal nucleophiles HO − , CH 3 O − , C 2 H 5 O − , and i-C 3 H 7 O − in reactions with methyl fluoride, anisole, and fluoroanisole. 10 Furthermore, a gas-phase α-effect has been shown to affect reactions of HOO − with methyl formate 11,12 and dimethyl methylphosphonate, 13 and theoretical studies support the premise that the α-effect has a component that can be attributed to intrinsic properties of the nucleophile. 14−19 The influence of solvent on the α-effect still remains intriguing.…”

Section: ■ Introductionmentioning

confidence: 91%

The α-Effect in Gas-Phase S_N2 Reactions of Microsolvated Anions: Methanol as a Solvent

et al. 2013

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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 gas-phase α-effect has recently been documented in studies of SN2 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 α-nucleophile HOO(-)(CH3OH) to that of microsolvated normal alkoxy nucleophiles, RO(-)(CH3OH) in reactions with CH3Cl and CH3Br. The results reveal enhanced reactivity of HOO(-)(CH3OH) 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 βnuc 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.

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“…Ions formed from methyl formate can also be reagents in the formation of larger molecules. For example, the enhanced reactivity of nucleophiles of HOO − , HO − , CH 3 O − and HCOO − (possible anions formed from HCOOCH 3 ) was demonstrated (Garver et al 2012). It is also interesting that at extremely low temperatures (like in the ISM) the considerable increase of the reactivity of HCOOCH 3 with OH was observed, and resulting reaction products could be a substrate for the subsequent chemical reactions leading to the formation of other compounds (Jimenez et al 2016).…”

Section: Introductionmentioning

confidence: 97%

“…To examine possible reactions in space, the interaction of methyl formate with atoms, ions and photons was studied (Lawson 2012;Garver et al 2012;Fantuzzi et al 2011), but almost no studies on the interaction of electrons with HCOOCH 3 are available. Photodissociation studies of methyl formate with soft X-rays (532.2 eV and 288.3 eV) have shown formation of several positive ions with the highest intensity of HCO + (Fantuzzi et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Dissociation of methyl formate (HCOOCH₃) molecules upon low-energy electron attachment

Feketeová

Pełc

Ribar

et al. 2018

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Context. The methyl formate molecule (HCOOCH 3 ) is considered to be a key molecule in astrochemistry. The abundance of this molecule in space depends on the stability upon irradiation with particles like low-energy electrons. Aims. We have investigated the decomposition of the molecule upon electron capture in the electron energy range from about 0 eV up to 15 eV. All experimentally obtained fragmentation channels of the molecular anion were investigated by quantum chemical calculations. Methods. A high resolution electron monochromator coupled with quadrupole mass spectrometer was used for the present laboratory experiment. Quantum chemical calculations of the electron affinities of the generated fragments, the thermodynamic thresholds and the activation barriers for the associated reaction channels were carried out to complement the experimental studies. Results. Electron attachment is shown to be a purely dissociative process for this molecule and proceeds within two electron energy regions of about 1 eV to 4 eV and from 5 eV to 14 eV. In our experiment five anionic fragments with m/z (and possible stoichiometric structure) 59 (C 2 H 3 O Conclusions. The low-energy electron induced dissociation of methyl formate differs from its isomers acetic acid and glycolaldehyde, which leads to possible chemical selectivity in the chemical evolution.

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The α-effect in elimination reactions and competing mechanisms in the gas phase

Cited by 15 publications

References 66 publications

The α-effect exhibited in gas-phase S_N2@N and S_N2@C reactions

The α-effect exhibited in gas-phase S_N2@N and S_N2@C reactions

The α-Effect in Gas-Phase S_N2 Reactions of Microsolvated Anions: Methanol as a Solvent

Dissociation of methyl formate (HCOOCH₃) molecules upon low-energy electron attachment

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The α-effect in elimination reactions and competing mechanisms in the gas phase

Cited by 15 publications

References 66 publications

The α-effect exhibited in gas-phase SN2@N and SN2@C reactions

The α-effect exhibited in gas-phase SN2@N and SN2@C reactions

The α-Effect in Gas-Phase SN2 Reactions of Microsolvated Anions: Methanol as a Solvent

Dissociation of methyl formate (HCOOCH3) molecules upon low-energy electron attachment

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The α-effect exhibited in gas-phase S_N2@N and S_N2@C reactions

The α-effect exhibited in gas-phase S_N2@N and S_N2@C reactions

The α-Effect in Gas-Phase S_N2 Reactions of Microsolvated Anions: Methanol as a Solvent

Dissociation of methyl formate (HCOOCH₃) molecules upon low-energy electron attachment