The Thio-Wittig Rearrangement of Deprotonated Allyl Methyl Sulfide. A Gas-Phase Unimolecular Isomerization Probed with a Variable Temperature Flowing Afterglow-Triple Quadrupole Device

1996 ◽  
Vol 118 (6) ◽  
pp. 1398-1407 ◽  
Author(s):  
Mohammad R. Ahmad ◽  
Gregg D. Dahlke ◽  
Steven R. Kass
Keyword(s):  
Gas Phase ◽  
Variable Temperature ◽  
Triple Quadrupole ◽  
Flowing Afterglow ◽  
Wittig Rearrangement ◽  
Methyl Sulfide

Unimolecular Rearrangements and Fragmentations in the Gas Phase: [1,3] Sigmatropic Isomerizations and [2 + 2] Cycloreversions

2003 ◽  
Vol 56 (5) ◽  
pp. 453 ◽  
Author(s):  
Mohammad R. Ahmad ◽  
Steven R. Kass
Keyword(s):  
Gas Phase ◽  
Wide Temperature Range ◽  
Variable Temperature ◽  
Collision Induced Dissociation ◽  
Triple Quadrupole ◽  
Flowing Afterglow ◽  
Temperature Range ◽  
Sigmatropic Rearrangements ◽  
Ion Molecule Reactions ◽  
Trimethylsilyl Ethers

Trimethylsilyl ethers of 3-buten-2-ol, 1-vinylcyclopropanol, 1-vinylcyclobutanol, and cyclobutanol were treated with fluoride over a wide temperature range (–40 to 300°C) in a variable-temperature flowing afterglow–triple quadrupole device. The structures of the resulting alkoxides and enolates were probed by ion–molecule reactions and their collision-induced dissociation (CID) spectra. Activation energies were obtained for several anion-accelerated [1,3] sigmatropic rearrangements and [2 + 2] cycloreversions. The mechanisms for these isomerizations and fragmentations (stepwise versus concerted) and their synthetic potential are discussed.

An experimental study of the reactivity of the hydroxide anion in the gas phase at room temperature, and its perturbation by hydration

1981 ◽  
Vol 59 (11) ◽  
pp. 1615-1621 ◽  
Author(s):  
Scott D. Tanner ◽  
Gervase I. Mackay ◽  
Diethard K. Bohme
Keyword(s):  
Experimental Study ◽  
Proton Transfer ◽  
Gas Phase ◽  
Rate Constants ◽  
Room Temperature ◽  
Gas Phase Reactions ◽  
Flowing Afterglow ◽  
Hydroxide Anion

Flowing afterglow measurements are reported which provide rate constants and product identifications at 298 ± 2 K for the gas-phase reactions of OH− with CH3OH, C2H5OH, CH3OCH3, CH2O, CH3CHO, CH3COCH3, CH2CO, HCOOH, HCOOCH3, CH2=C=CH2, CH3—C≡CH, and C6H5CH3. The main channels observed were proton transfer and solvation of the OH−. Hydration with one molecule of H2O was observed either to reduce the rate slightly and lead to products which are the hydrated analogues of the "nude" reaction, or to stop the reaction completely, k ≤ 10−12 cm3 molecule−1 s−1. The reaction of OH−•H2O with CH3—C≡CH showed an uncertain intermediate behaviour.

Gas-phase proton-transfer reactions of the hydronium ion at 298 K

1979 ◽  
Vol 57 (12) ◽  
pp. 1518-1523 ◽  
Author(s):  
Gervase I. Mackay ◽  
Scott D. Tanner ◽  
Alan C. Hopkinson ◽  
Diethard K. Bohme
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Rate Constants ◽  
Transfer Reactions ◽  
Flowing Afterglow ◽  
Hydronium Ion ◽  
Proton Transfer Reactions

Rate constants measured with the flowing afterglow technique at 298 ± 2 K are reported for the proton-transfer reactions of H3O+ with CH2O, CH3CHO, (CH3)2CO, HCOOH, CH3COOH, HCOOCH3, CH3OH, C2H5OH, (CH3)2O, and CH2CO. Dissociative proton-transfer was observed only with CH3COOH. The rate constants are compared with the predictions of various theories for ion–molecule collisions. The protonation is discussed in terms of the energetics and mechanisms of various modes of dissociation.

Carbanion Rearrangements in the Gas Phase: The Unusual Claisen Rearrangement of Deprotonated Allyl Vinyl Ether

1990 ◽  
Vol 43 (9) ◽  
pp. 1479 ◽  
Author(s):  
PCH Eichinger ◽  
JH Bowie
Keyword(s):  
Gas Phase ◽  
Vinyl Ether ◽  
Condensed Phase ◽  
Claisen Rearrangement ◽  
Negative Ions ◽  
Marked Contrast ◽  
Wittig Rearrangement ◽  
Major Reaction

Allyl vinyl ether is reported to undergo a facile Wittig rearrangement to yield penta-1,4-dien-3-ol under base- catalysed conditions in the condensed phase. In marked contrast, the Wittig rearrangement is not a major reaction in the gas phase. Instead, initial rearrangement occurs by a Claisen process and subsequent fragmentations involve some of the most complex interconversions yet proposed for negative ions.

scholarly journals Dimerization of Acetic Acid in the Gas Phase—NMR Experiments and Quantum-Chemical Calculations

Molecules ◽  
2020 ◽  
Vol 25 (9) ◽  
pp. 2150 ◽  
Author(s):  
Ondřej Socha ◽  
Martin Dračínský
Keyword(s):  
Acetic Acid ◽  
Gas Phase ◽  
Low Temperatures ◽  
Variable Temperature ◽  
Glass Tube ◽  
Variable Pressure ◽  
Liquid Phases ◽  
Donor And Acceptor ◽  
Moller Plesset ◽  
Triple Excitation

Due to the nature of the carboxylic group, acetic acid can serve as both a donor and acceptor of a hydrogen bond. Gaseous acetic acid is known to form cyclic dimers with two strong hydrogen bonds. However, trimeric and various oligomeric structures have also been hypothesized to exist in both the gas and liquid phases of acetic acid. In this work, a combination of gas-phase NMR experiments and advanced computational approaches were employed in order to validate the basic dimerization model of gaseous acetic acid. The gas-phase experiments performed in a glass tube revealed interactions of acetic acid with the glass surface. On the other hand, variable-temperature and variable-pressure NMR parameters obtained for acetic acid in a polymer insert provided thermodynamic parameters that were in excellent agreement with the MP2 (the second order Møller–Plesset perturbation theory) and CCSD(T) (coupled cluster with single, double and perturbative triple excitation) calculations based on the basic dimerization model. A slight disparity between the theoretical dimerization model and the experimental data was revealed only at low temperatures. This observation might indicate the presence of other, entropically disfavored, supramolecular structures at low temperatures.

Absolute gas-phase acidities of CH3NH2, C2H5NH2, (CH3)2 NH, and (CH3)3N

1976 ◽  
Vol 54 (10) ◽  
pp. 1624-1642 ◽  
Author(s):  
Gervase I. Mackay ◽  
Ronald S. Hemsworth ◽  
Diethard K. Bohme
Keyword(s):  
Equilibrium Constant ◽  
Gas Phase ◽  
Equilibrium Constants ◽  
Heats Of Formation ◽  
Molecular Orbital Calculations ◽  
Electron Affinities ◽  
Flowing Afterglow ◽  
Experimental Assessment ◽  
Gas Phase Acidity ◽  
Conjugate Bases

The flowing afterglow technique has been employed in measurements of the rate and equilibrium constants at 296 ± 2 K for reactions of the type[Formula: see text]and[Formula: see text]where R1 and R2 may be H, CH3, or C2H5. The equilibrium constant measurements provided absolute values for the intrinsic (gas-phase) acidities of the Brønsted acids CH3NH2, C2H5NH2, (CH3)2NH, and (CH3)3N, the heats of formation of their conjugate bases, and the electron affinities of the corresponding radicals R1R2N. Proton removal energies, ΔG0298/(kcal mol−1), were determined to be 395.7 ± 0.7 for [Formula: see text] 391.7 ± 0.7 for [Formula: see text] 389.2 ± 0.6 for [Formula: see text] and > 396 for [Formula: see text] Heats of formation, ΔH0f.,298, were determined to be 30.5 ± 1.5 for CH3NH−, 21.2 ± 1.5 for C2H5NH−, and 24.7 ± 1.4 for (CH3)2N−. Electron affinities (in kcal mol−1) were determined to be 13.1 ± 3.5 for CH3NH, 17 ± 4 for C2H5NH, and 14.3 ± 3.4 for (CH3)2N. These results quantify earlier conclusions regarding the intrinsic effects of substituents on the gas-phase acidity of amines and provide an experimental assessment of recent molecular orbital calculations of proton removal energies for alkylamines.

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