The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
Witold Danikiewicz - One of the best experts on this subject based on the ideXlab platform.
-
Gas-Phase Reactions of Dimethyl Disulfide with Aliphatic Carbanions - A Mass Spectrometry and Computational Study
Journal of The American Society for Mass Spectrometry, 2018Co-Authors: Barbara Franczuk, Witold DanikiewiczAbstract:Ion-molecule reactions of Me_2S_2 with a wide range of aliphatic Carbanions differing by structure and proton affinity values have been studied in the gas phase using mass spectrometry techniques and DFT calculations. The analysis of the spectra shows a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the Carbanion. Product ions of thiophilic reaction ( m/z 47), S_N2 ( m/z 79), and E2 elimination – addition sequence of reactions ( m/z 93) can be observed. Primary products of thiophilic reaction can undergo subsequent S_N2 and proton transfer reactions. Gibbs free energy profiles calculated for experimentally observed reactions using PBE0/6-311+G(2d,p) method show good agreement with experimental results. Graphical Abstract ᅟ
-
gas phase reactions of methyl thiocyanate with aliphatic Carbanions a mass spectrometry and computational study
Rapid Communications in Mass Spectrometry, 2016Co-Authors: Barbara Repec, Kacper Blaziak, Witold DanikiewiczAbstract:Rationale Methyl thiocyanate, like other organic thiocyanates, is a molecule with many electrophilic reactive sites and it has many synthetic applications. For better understanding of the intrinsic reactivity of alkyl thiocyanates against nucleophiles it was important to study gas-phase reactions of methyl thiocyanate with Carbanions differing by structure and proton affinity values. Methods All experiments were performed using a modified API 365 triple quadrupole mass spectrometer equipped with a TurboIonSpray electrospray ionization (ESI) source. Carbanions were generated in the ESI source by decarboxylation of the respective carboxylic acid anions. Methyl thiocyanate was delivered as a vapor with nitrogen used as a collision gas to the collision cell where the reactions take place. Results Mass spectra recorded for the gas-phase reactions of five aliphatic Carbanions with methyl thiocyanate showed a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the Carbanion. The pathways considered are: SN2 nucleophilic substitution, cyanophilic reaction, thiophilic reaction and proton transfer, followed in some instances by subsequent transformations. The proposed reaction pathways are supported by density functional theory (DFT) calculations. Conclusions Our preliminary experiments showed that mass spectrometry together with quantum chemical calculations is a good tool for studying gas-phase reactions of alkyl thiocyanates with Carbanions. In the gas phase all four theoretically possible products can be observed and their formation can be rationalized by the results of the modelling of the reaction energy profiles. Copyright © 2016 John Wiley & Sons, Ltd.
-
Gas‐phase reactions of methyl thiocyanate with aliphatic Carbanions – A mass spectrometry and computational study
Rapid Communications in Mass Spectrometry, 2016Co-Authors: Barbara Repec, Kacper Błaziak, Witold DanikiewiczAbstract:Rationale Methyl thiocyanate, like other organic thiocyanates, is a molecule with many electrophilic reactive sites and it has many synthetic applications. For better understanding of the intrinsic reactivity of alkyl thiocyanates against nucleophiles it was important to study gas-phase reactions of methyl thiocyanate with Carbanions differing by structure and proton affinity values. Methods All experiments were performed using a modified API 365 triple quadrupole mass spectrometer equipped with a TurboIonSpray electrospray ionization (ESI) source. Carbanions were generated in the ESI source by decarboxylation of the respective carboxylic acid anions. Methyl thiocyanate was delivered as a vapor with nitrogen used as a collision gas to the collision cell where the reactions take place. Results Mass spectra recorded for the gas-phase reactions of five aliphatic Carbanions with methyl thiocyanate showed a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the Carbanion. The pathways considered are: SN2 nucleophilic substitution, cyanophilic reaction, thiophilic reaction and proton transfer, followed in some instances by subsequent transformations. The proposed reaction pathways are supported by density functional theory (DFT) calculations. Conclusions Our preliminary experiments showed that mass spectrometry together with quantum chemical calculations is a good tool for studying gas-phase reactions of alkyl thiocyanates with Carbanions. In the gas phase all four theoretically possible products can be observed and their formation can be rationalized by the results of the modelling of the reaction energy profiles. Copyright © 2016 John Wiley & Sons, Ltd.
-
gas phase reactions of methyl thiocyanate with aliphatic Carbanions a mass spectrometry and computational study
Rapid Communications in Mass Spectrometry, 2016Co-Authors: Barbara Repec, Kacper Blaziak, Witold DanikiewiczAbstract:Rationale Methyl thiocyanate, like other organic thiocyanates, is a molecule with many electrophilic reactive sites and it has many synthetic applications. For better understanding of the intrinsic reactivity of alkyl thiocyanates against nucleophiles it was important to study gas-phase reactions of methyl thiocyanate with Carbanions differing by structure and proton affinity values. Methods All experiments were performed using a modified API 365 triple quadrupole mass spectrometer equipped with a TurboIonSpray electrospray ionization (ESI) source. Carbanions were generated in the ESI source by decarboxylation of the respective carboxylic acid anions. Methyl thiocyanate was delivered as a vapor with nitrogen used as a collision gas to the collision cell where the reactions take place. Results Mass spectra recorded for the gas-phase reactions of five aliphatic Carbanions with methyl thiocyanate showed a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the Carbanion. The pathways considered are: SN2 nucleophilic substitution, cyanophilic reaction, thiophilic reaction and proton transfer, followed in some instances by subsequent transformations. The proposed reaction pathways are supported by density functional theory (DFT) calculations. Conclusions Our preliminary experiments showed that mass spectrometry together with quantum chemical calculations is a good tool for studying gas-phase reactions of alkyl thiocyanates with Carbanions. In the gas phase all four theoretically possible products can be observed and their formation can be rationalized by the results of the modelling of the reaction energy profiles. Copyright © 2016 John Wiley & Sons, Ltd.
Barbara Repec - One of the best experts on this subject based on the ideXlab platform.
-
gas phase reactions of methyl thiocyanate with aliphatic Carbanions a mass spectrometry and computational study
Rapid Communications in Mass Spectrometry, 2016Co-Authors: Barbara Repec, Kacper Blaziak, Witold DanikiewiczAbstract:Rationale Methyl thiocyanate, like other organic thiocyanates, is a molecule with many electrophilic reactive sites and it has many synthetic applications. For better understanding of the intrinsic reactivity of alkyl thiocyanates against nucleophiles it was important to study gas-phase reactions of methyl thiocyanate with Carbanions differing by structure and proton affinity values. Methods All experiments were performed using a modified API 365 triple quadrupole mass spectrometer equipped with a TurboIonSpray electrospray ionization (ESI) source. Carbanions were generated in the ESI source by decarboxylation of the respective carboxylic acid anions. Methyl thiocyanate was delivered as a vapor with nitrogen used as a collision gas to the collision cell where the reactions take place. Results Mass spectra recorded for the gas-phase reactions of five aliphatic Carbanions with methyl thiocyanate showed a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the Carbanion. The pathways considered are: SN2 nucleophilic substitution, cyanophilic reaction, thiophilic reaction and proton transfer, followed in some instances by subsequent transformations. The proposed reaction pathways are supported by density functional theory (DFT) calculations. Conclusions Our preliminary experiments showed that mass spectrometry together with quantum chemical calculations is a good tool for studying gas-phase reactions of alkyl thiocyanates with Carbanions. In the gas phase all four theoretically possible products can be observed and their formation can be rationalized by the results of the modelling of the reaction energy profiles. Copyright © 2016 John Wiley & Sons, Ltd.
-
Gas‐phase reactions of methyl thiocyanate with aliphatic Carbanions – A mass spectrometry and computational study
Rapid Communications in Mass Spectrometry, 2016Co-Authors: Barbara Repec, Kacper Błaziak, Witold DanikiewiczAbstract:Rationale Methyl thiocyanate, like other organic thiocyanates, is a molecule with many electrophilic reactive sites and it has many synthetic applications. For better understanding of the intrinsic reactivity of alkyl thiocyanates against nucleophiles it was important to study gas-phase reactions of methyl thiocyanate with Carbanions differing by structure and proton affinity values. Methods All experiments were performed using a modified API 365 triple quadrupole mass spectrometer equipped with a TurboIonSpray electrospray ionization (ESI) source. Carbanions were generated in the ESI source by decarboxylation of the respective carboxylic acid anions. Methyl thiocyanate was delivered as a vapor with nitrogen used as a collision gas to the collision cell where the reactions take place. Results Mass spectra recorded for the gas-phase reactions of five aliphatic Carbanions with methyl thiocyanate showed a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the Carbanion. The pathways considered are: SN2 nucleophilic substitution, cyanophilic reaction, thiophilic reaction and proton transfer, followed in some instances by subsequent transformations. The proposed reaction pathways are supported by density functional theory (DFT) calculations. Conclusions Our preliminary experiments showed that mass spectrometry together with quantum chemical calculations is a good tool for studying gas-phase reactions of alkyl thiocyanates with Carbanions. In the gas phase all four theoretically possible products can be observed and their formation can be rationalized by the results of the modelling of the reaction energy profiles. Copyright © 2016 John Wiley & Sons, Ltd.
-
gas phase reactions of methyl thiocyanate with aliphatic Carbanions a mass spectrometry and computational study
Rapid Communications in Mass Spectrometry, 2016Co-Authors: Barbara Repec, Kacper Blaziak, Witold DanikiewiczAbstract:Rationale Methyl thiocyanate, like other organic thiocyanates, is a molecule with many electrophilic reactive sites and it has many synthetic applications. For better understanding of the intrinsic reactivity of alkyl thiocyanates against nucleophiles it was important to study gas-phase reactions of methyl thiocyanate with Carbanions differing by structure and proton affinity values. Methods All experiments were performed using a modified API 365 triple quadrupole mass spectrometer equipped with a TurboIonSpray electrospray ionization (ESI) source. Carbanions were generated in the ESI source by decarboxylation of the respective carboxylic acid anions. Methyl thiocyanate was delivered as a vapor with nitrogen used as a collision gas to the collision cell where the reactions take place. Results Mass spectra recorded for the gas-phase reactions of five aliphatic Carbanions with methyl thiocyanate showed a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the Carbanion. The pathways considered are: SN2 nucleophilic substitution, cyanophilic reaction, thiophilic reaction and proton transfer, followed in some instances by subsequent transformations. The proposed reaction pathways are supported by density functional theory (DFT) calculations. Conclusions Our preliminary experiments showed that mass spectrometry together with quantum chemical calculations is a good tool for studying gas-phase reactions of alkyl thiocyanates with Carbanions. In the gas phase all four theoretically possible products can be observed and their formation can be rationalized by the results of the modelling of the reaction energy profiles. Copyright © 2016 John Wiley & Sons, Ltd.
Kacper Blaziak - One of the best experts on this subject based on the ideXlab platform.
-
gas phase reactions of methyl thiocyanate with aliphatic Carbanions a mass spectrometry and computational study
Rapid Communications in Mass Spectrometry, 2016Co-Authors: Barbara Repec, Kacper Blaziak, Witold DanikiewiczAbstract:Rationale Methyl thiocyanate, like other organic thiocyanates, is a molecule with many electrophilic reactive sites and it has many synthetic applications. For better understanding of the intrinsic reactivity of alkyl thiocyanates against nucleophiles it was important to study gas-phase reactions of methyl thiocyanate with Carbanions differing by structure and proton affinity values. Methods All experiments were performed using a modified API 365 triple quadrupole mass spectrometer equipped with a TurboIonSpray electrospray ionization (ESI) source. Carbanions were generated in the ESI source by decarboxylation of the respective carboxylic acid anions. Methyl thiocyanate was delivered as a vapor with nitrogen used as a collision gas to the collision cell where the reactions take place. Results Mass spectra recorded for the gas-phase reactions of five aliphatic Carbanions with methyl thiocyanate showed a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the Carbanion. The pathways considered are: SN2 nucleophilic substitution, cyanophilic reaction, thiophilic reaction and proton transfer, followed in some instances by subsequent transformations. The proposed reaction pathways are supported by density functional theory (DFT) calculations. Conclusions Our preliminary experiments showed that mass spectrometry together with quantum chemical calculations is a good tool for studying gas-phase reactions of alkyl thiocyanates with Carbanions. In the gas phase all four theoretically possible products can be observed and their formation can be rationalized by the results of the modelling of the reaction energy profiles. Copyright © 2016 John Wiley & Sons, Ltd.
-
gas phase reactions of methyl thiocyanate with aliphatic Carbanions a mass spectrometry and computational study
Rapid Communications in Mass Spectrometry, 2016Co-Authors: Barbara Repec, Kacper Blaziak, Witold DanikiewiczAbstract:Rationale Methyl thiocyanate, like other organic thiocyanates, is a molecule with many electrophilic reactive sites and it has many synthetic applications. For better understanding of the intrinsic reactivity of alkyl thiocyanates against nucleophiles it was important to study gas-phase reactions of methyl thiocyanate with Carbanions differing by structure and proton affinity values. Methods All experiments were performed using a modified API 365 triple quadrupole mass spectrometer equipped with a TurboIonSpray electrospray ionization (ESI) source. Carbanions were generated in the ESI source by decarboxylation of the respective carboxylic acid anions. Methyl thiocyanate was delivered as a vapor with nitrogen used as a collision gas to the collision cell where the reactions take place. Results Mass spectra recorded for the gas-phase reactions of five aliphatic Carbanions with methyl thiocyanate showed a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the Carbanion. The pathways considered are: SN2 nucleophilic substitution, cyanophilic reaction, thiophilic reaction and proton transfer, followed in some instances by subsequent transformations. The proposed reaction pathways are supported by density functional theory (DFT) calculations. Conclusions Our preliminary experiments showed that mass spectrometry together with quantum chemical calculations is a good tool for studying gas-phase reactions of alkyl thiocyanates with Carbanions. In the gas phase all four theoretically possible products can be observed and their formation can be rationalized by the results of the modelling of the reaction energy profiles. Copyright © 2016 John Wiley & Sons, Ltd.
John P. Richard - One of the best experts on this subject based on the ideXlab platform.
-
origin of free energy barriers of decarboxylation and the reverse process of co2 capture in dimethylformamide and in water
Journal of the American Chemical Society, 2021Co-Authors: Shaoyuan Zhou, John P. Richard, Ronald Kluger, Bach T Nguyen, Jiali GaoAbstract:In aqueous solution, biological decarboxylation reactions proceed irreversibly to completion, whereas the reverse carboxylation processes are typically powered by the hydrolysis of ATP. The exchange of the carboxylate of ring-substituted arylacetates with isotope-labeled CO2 in polar aprotic solvents reported recently suggests a dramatic change in the partition of reaction pathways. Yet, there is little experimental data pertinent to the kinetic barriers for protonation and thermodynamic data on CO2 capture by the Carbanions of decarboxylation reactions. Employing a combined quantum mechanical and molecular mechanical simulation approach, we investigated the decarboxylation reactions of a series of organic carboxylate compounds in aqueous and in dimethylformamide solutions, revealing that the reverse carboxylation barriers in solution are fully induced by solvent effects. A linear Bell-Evans-Polanyi relationship was found between the rates of decarboxylation and the Gibbs energies of reaction, indicating diminishing recombination barriers in DMF. In contrast, protonation of the Carbanions by the DMF solvent has large free energy barriers, rendering the competing exchange of isotope-labeled CO2 reversible in DMF. The finding of an intricate interplay of Carbanion stability and solute-solvent interaction in decarboxylation and carboxylation could be useful to designing novel materials for CO2 capture.
-
proton transfer from c 6 of uridine 5 monophosphate catalyzed by orotidine 5 monophosphate decarboxylase formation and stability of a vinyl Carbanion intermediate and the effect of a 5 fluoro substituent
Journal of the American Chemical Society, 2012Co-Authors: Wing Yin Tsang, Mckay B Wood, Freeman M Wong, J A Gerlt, Tina L Amyes, John P. RichardAbstract:The exchange for deuterium of the C-6 protons of uridine 5'-monophosphate (UMP) and 5-fluorouridine 5'-monophosphate (F-UMP) catalyzed by yeast orotidine 5'-monophosphate decarboxylase (ScOMPDC) at pD 6.5-9.3 and 25 °C was monitored by (1)H NMR spectroscopy. Deuterium exchange proceeds by proton transfer from C-6 of the bound nucleotide to the deprotonated side chain of Lys-93 to give the enzyme-bound vinyl Carbanion. The pD-rate profiles for k(cat) give turnover numbers for deuterium exchange into enzyme-bound UMP and F-UMP of 1.2 × 10(-5) and 0.041 s(-1), respectively, so that the 5-fluoro substituent results in a 3400-fold increase in the first-order rate constant for deuterium exchange. The binding of UMP and F-UMP to ScOMPDC results in 0.5 and 1.4 unit decreases, respectively, in the pK(a) of the side chain of the catalytic base Lys-93, showing that these nucleotides bind preferentially to the deprotonated enzyme. We also report the first carbon acid pK(a) values for proton transfer from C-6 of uridine (pK(CH) = 28.8) and 5-fluorouridine (pK(CH) = 25.1) in aqueous solution. The stabilizing effects of the 5-fluoro substituent on C-6 Carbanion formation in solution (5 kcal/mol) and at ScOMPDC (6 kcal/mol) are similar. The binding of UMP and F-UMP to ScOMPDC results in a greater than 5 × 10(9)-fold increase in the equilibrium constant for proton transfer from C-6, so that ScOMPDC stabilizes the bound vinyl Carbanions, relative to the bound nucleotides, by at least 13 kcal/mol. The pD-rate profile for k(cat)/K(m) for deuterium exchange into F-UMP gives the intrinsic second-order rate constant for exchange catalyzed by the deprotonated enzyme as 2300 M(-1) s(-1). This was used to calculate a total rate acceleration for ScOMPDC-catalyzed deuterium exchange of 3 × 10(10) M(-1), which corresponds to a transition-state stabilization for deuterium exchange of 14 kcal/mol. We conclude that a large portion of the total transition-state stabilization for the decarboxylation of orotidine 5'-monophosphate can be accounted for by stabilization of the enzyme-bound vinyl Carbanion intermediate of the stepwise reaction.
-
Claisen-type addition of glycine to a pyridoxal iminium ion in water.
The Journal of organic chemistry, 2006Co-Authors: Krisztina Toth, Lauren M. Gaskell, John P. RichardAbstract:formula chem. The 5'-deoxypyridoxal stabilized glycine Carbanion has been generated in water at neutral and mildly basic pH. At pH < 7, this Carbanion reacts mainly with the carbonyl carbon of 1 to form a stable Claisen-type adduct. At pH ≥ 8, this Carbanion reacts with the iminium carbon of the pyridoxalglycine iminium ion to form the second Claisen-type adduct 3 as the major reaction product.
Michael R. Crampton - One of the best experts on this subject based on the ideXlab platform.
-
Carbanion reactivity, kinetic and equilibrium studies of σ-adduct formation and elimination in the reactions of 4-nitrobenzofurazan derivatives with nitroalkane anions
Organic and Biomolecular Chemistry, 2007Co-Authors: Basim H. M. Asghar, Michael R. CramptonAbstract:1 H NMR studies are reported of the reactions in [2H6]-DMSO of 4-nitrobenzofurazan, 2a, and its 7-chloro- and 7-methoxy-derivatives, 2b and 2c respectively, with anions derived from nitromethane, 3, nitroethane, 4, and 2-nitropropane, 5. The initial reactions result in σ-adduct formation by Carbanion attack at the 5-position of 2a–c and in the case of reaction of 2a with 5 the adduct at the 7-position is also observed. These reactions may be followed by base catalysed elimination of nitrous acid to yield anionic alkene derivatives. Kinetic and equilibrium measurements of these reactions were made spectrophotometrically in methanol. The carbon nucleophilicities of the Carbanions decrease in the order 3 > 4 > 5, as also found in their reactions with benzhydrylium cations, and are much lower than the nucleophilicities of some cyano-substituted Carbanions. Comparison with corresponding σ-adduct forming reactions of 1,3,5-trinitrobenzene, TNB, show that here 2 and TNB have similar electrophilicity, although the value of the intrinsic rate coefficient ko = 0.05, for reaction of 2 is rather lower than that, ko = 0.20, for the TNB reactions. Literature data suggest that for reaction with a variety of nucleophiles 2 and TNB show similar electrophilicities. Measurements of the rates of elimination of nitrous acid from some 5-adducts in methanol catalysed by methoxide ions are reported. Values of rate constants may be influenced both by steric requirements at the reaction centre and by the electronic effects of the 7-substituent.
-
Carbanion reactivity; kinetics of the reactions of benzyl cyanide anions with aromatic nitro-compounds
Journal of the Chemical Society Perkin Transactions 2, 1995Co-Authors: John H. Atherton, Michael R. Crampton, Gaynor L. Duffield, J. Andrew StevensAbstract:Rate and equilibrium measurements are reported for the reactions in methanol of Carbanions derived from 12 ring-substituted benzyl cyanides with 1,3,5-trinitrobenzene to give σ-adducts. Some data for reaction of the Carbanions with 4-nitrobenzofuroxan were also measured. With increasing Carbanion reactivity, rate constants approach a limit of just below 109 dm3 mol–1 s–1. Intrinsic reactivities of Carbanions in σ-adduct forming reactions and in proton transfer reactions are compared.