Gas-phase acidities: alkanethiols

Bartmess, John E.; McIver, Robert T.

doi:10.1021/ja00454a049

Cited by 20 publications

(5 citation statements)

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“…No acceptable solution for cleavage chemistry has yet been found for the thietanes. While thietane itself is the most reactive parent four-membered heterocycle, we have found, in accord with the results of Molina et al, 22,23 rather unremarkable substituent effects accompany cleavage.…”

Section: Resultssupporting

confidence: 92%

Is nucleophilic cleavage chemistry practical for 4-membered heterocycles?

Banks

2009

Org. Biomol. Chem.

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A computational study at the MP2(Full)/6-311++G(d,p)//MP2(Full)/6-31+G(d) level of the ammonolysis of halogen substituted azetidines, oxetanes and thietanes was performed in the gas phase and in the commonly used solvent, acetonitrile. Using the free energy of activation of a benchmark reaction for evaluation of synthetic viability, several haloazetidines and oxetanes that possessed the required reactivity were identified; however, no substituted thietane investigated herein was determined to be synthetically useful under the mild conditions selected for this study. In the case of the azetidines, the side reaction of displacement of halide ion was determined to be the preferred reaction course in acetonitrile; however, the amino product of the reactions of the 2-haloazetidines cleaved at an acceptable rate under mild conditions. For the oxetane derivatives investigated, 2-fluorooxetane proved to be a direct source of ring cleavage product. Nucleophilic cleavage of halogen-substituted azetidines and oxetanes is predicted to be a viable source of functionalized three-carbon moieties under mild conditions in organic synthesis.

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Section: Resultssupporting

confidence: 92%

Is nucleophilic cleavage chemistry practical for 4-membered heterocycles?

Banks

2009

Org. Biomol. Chem.

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“…[9a] In the theoretical proton-transfer limit, protein ions that are less basic than the neutral molecules from the ESI source should not be formed; [9b] that is,protein ions should readily transfer protons to evaporating,neutral solvent molecules and not survive ESI.Thet hermochemistry of proton-transfer reactions underpin the rationalization of many chemical reactions.T he investigation of gas-phase basicities [GBs,E q. (1)] of mole-MðgÞþH þ ðgÞ!MH þ ðgÞ DG ¼ ÀGBðMÞ ð1Þcules has been as ignificant undertaking in gas-phase ion chemistry since the late 1960s [10] and values have been determined for over at housand compounds.F or organic molecules,t hese values range from 505 kJ mol À1 for tetrafluoromethane to more than 1000 kJ mol À1 for highly basic molecules such as arginine (GB = 1007 kJ mol À1 ). Forp ositive ions,G Bs are lower than the corresponding neutral molecules owing to the Coulombic repulsion between the proton and cationic molecule [Eq.(2)].…”

mentioning

confidence: 99%

“…cules has been as ignificant undertaking in gas-phase ion chemistry since the late 1960s [10] and values have been determined for over at housand compounds.F or organic molecules,t hese values range from 505 kJ mol À1 for tetrafluoromethane to more than 1000 kJ mol À1 for highly basic molecules such as arginine (GB = 1007 kJ mol À1 ). Forp ositive ions,G Bs are lower than the corresponding neutral molecules owing to the Coulombic repulsion between the proton and cationic molecule [Eq.…”

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confidence: 99%

Highly Charged Protein Ions: The Strongest Organic Acids to Date

et al. 2017

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The basicity of highly protonated cytochrome c (cyt c) and myoglobin (myo) ions were investigated using tandem mass spectrometry,i on-molecule reactions (IMRs), and theoretical calculations as af unction of charge state. Surprisingly,h ighly charged protein ions (HCPI) can readily protonate non-polar molecules and inert gases,i ncluding Ar, O 2 ,a nd N 2 in thermal IMRs.T he most HCPIs that can be observed are over 130 kJ mol À1 less basic than the least basic neutral organic molecules known( tetrafluoromethane and methane). Based on theoretical calculations,itispredicted that protonated cyt ca nd myo ions should spontaneously lose ap roton to vacuum for charge states in which every third residue is protonated. In this study,H CPIs are formed where every fourth residue on average is protonated. These results indicate that protein ions in higher charge states can be formed using al ow-pressure ion source to reduce proton-transfer reactions between protein ions and gases from the atmosphere.Electrospray ionization (ESI) is renowned for its ability to form intact, gaseous,m ultiply charged protein ions for rapid and sensitive detection by mass spectrometry. [1] However,the mechanism by which protein ions are formed in ESI is controversial and continues to be actively debated. Thet wo primary competing models to explain ion formation are known as the charge residue model (CRM) [2] and the ion evaporation model (IEM). [3] In both models,a sn eutral molecules evaporate from ac harged droplet, the electric field at the surface of the droplet increases,w hich initiates fission. [4] Such droplet fission events result in the emission of afine stream of smaller droplets that remove less than 1% of the mass but more than 30 %o ft he charge of the precursor droplet. [4,5] In the CRM, sequential droplet evaporation and Coulombic fission events yield acharged droplet that contains asingle analyte ion, which evaporates to dryness via the loss of neutral solvent molecules.Inthe IEM, the electric field on the surface of ah ighly charged droplet near the moment of ion formation is sufficient to result in the ejection of an analyte ion from the surface of the ionic droplet. Themajority of current evidence indicates that fully desolvated protein ions formed from buffered aqueous solutions are formed by the CRM. Charge carriers such as solvated hydronium ions can be lost via ion evaporation during the ESI process. [6] Recently,the chain-ejection model (CEM), [7] which is related to the IEM, was proposed to explain the formation of protein ions from denaturing solutions based on results from molecular dynamics simulations. [7] In the CEM, ad enatured, disordered protein chain is ejected from ah ighly charged, nanometer-sized ionic droplet. As the protein ion protrudes and is ejected from the droplet, proton transfer to the protein ion can occur. However,t he mechanism by which highly charged protein ions (HCPIs) are formed from denaturing solutions is less well established with evidence supporting both the CRM [8] and CEM/IEM having be...

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“…The alcohol deprotonation enthalpy in vacuo has been calculated as the reference state. The experimental value for this process is known as 1579.5 kJ/mol23 and is compared with the calculated deprotonation enthalpies for a molecule of ethanol that is hydrogen bonded to the oxygen atom in S‐methylated tri‐ tert ‐butoxysilanethiol and with the ethanol molecule in complex 5c , which we consider as an accurate structural model for the ADH active site.…”

Section: Resultsmentioning

confidence: 99%

Modeling of the Alcohol Dehydrogenase Active Site: Two Different Modes of Alcohol Binding in Crystals of Zinc and Cadmium Tri‐tert‐butoxysilanethiolates Evidenced by X‐ray Diffraction and Solid‐State Vibrational Spectroscopy

et al. 2009

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Keywords: Zinc / Cadmium / N,S ligands / Structure elucidation / Enzyme models / Coordination modes Two different modes of binding methanol and ethanol were found in crystals of heteroleptic zinc and cadmium complexes with MS 2 NO 2 and MS 2 NO kernels and with a general formula M(RS) 2 (im) (M = Zn, Cd; RS = tri-tert-butoxysilanethiolate; im = imidazole, 2-methylimidazole, 2-ethylimidazole). Alcohol molecules are either trapped in the crystal lattice by NH···O and OH···S hydrogen bonds or directly coordinated to the metal centre. The complexes were studied by X-ray diffraction, solid state FTIR and

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Gas-phase acidities: alkanethiols

Cited by 20 publications

References 4 publications

Is nucleophilic cleavage chemistry practical for 4-membered heterocycles?

Is nucleophilic cleavage chemistry practical for 4-membered heterocycles?

Highly Charged Protein Ions: The Strongest Organic Acids to Date

Modeling of the Alcohol Dehydrogenase Active Site: Two Different Modes of Alcohol Binding in Crystals of Zinc and Cadmium Tri‐tert‐butoxysilanethiolates Evidenced by X‐ray Diffraction and Solid‐State Vibrational Spectroscopy

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