Methyl cation affinities

McMahon, T. B.; Heinis, Thomas; Nicol, Gordon; Hovey, Jamey K.; Kebarle, P.

doi:10.1021/ja00231a002

Cited by 107 publications

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“…The results obtained in the present study suggest that the nitriles are not symmetrically bound to the methyl cation since it is well-established that methyl cation affinities do correlate with proton affinities of a large number of bases. 15 To better understand the structure and dissociation behavior of the methyl cation/nitrile cluster ions, energy-resolved collision-induced dissociation experiments were performed on a model system, the cluster ion composed of the methyl cation, acetonitrile and butyronitrile. The dissociation of the cluster ion yielded two fragments having mass-to-charge 56 Th and 84 Th, corresponding to the individual methylated monomers.…”

Section: Resultsmentioning

confidence: 99%

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Structural Characterization of Clusters Formed from Alkyl Nitriles and the Methyl Cation

Denault¹,

Wang²,

Cooks³

et al. 2000

J. Phys. Chem. A

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Cluster ions composed of the alkyl nitriles, acetonitrile (CH 3 CN) and butyronitrile (C 3 H 7 CN), and the methyl cation (CH 3 + ) have been examined in an effort to study methyl cation affinities and the intrinsic nucleophilicity of these bases. Structural characterization of the gas-phase dimeric adduct ions was achieved via multiple stage mass spectrometry (MS n ) experiments and by quantum mechanical calculations. The kinetic method was used as a diagnostic tool in determining the structure of the dimeric adduct: the results of tandem mass spectrometry (MS 2 ) experiments are found to provide ratios which exclude loosely bonded dimers based on the thermochemistry of the constituent monomers, and which are consistent with a mixture of noninterconverting covalently bonded structures predicted by ab initio calculations. These clusters are bound such that one nitrile is N-methylated and the second nitrile is bound covalently to the carbon of the methylated cyano group. Collision-induced dissociation of this cluster ion results in the loss of a single neutral nitrile whereas both N-methylated nitriles should be formed upon dissociation of a loosely bound dimer with the greater fragment ion abundance corresponding to the nitrile having the higher CH 3 + affinity. Ab initio calculations show a large barrier between the two isomeric forms of the dimeric cluster and this precludes intramolecular methyl cation transfer between the nitriles. The effects of fluorine substitution at the methyl cation, i.e., CH 2 F + and CF 3 + , on the adducts of the nitriles greatly affects the stability order of the methylated nitrile monomers and dimeric adducts, and thus the abundance ratios of the MS/MS fragments. As the number of fluorine atoms in the cation is increased, the methylated nitrile becomes less stable relative to the dimeric cluster ion.

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Section: Resultsmentioning

confidence: 99%

“…[13][14][15][16] However, because the methyl transfer reaction is usually slow and reaches equilibrium at long times, MCAs have often been determined by measuring enthalpies of formation.…”

Section: Introductionmentioning

confidence: 99%

Structural Characterization of Clusters Formed from Alkyl Nitriles and the Methyl Cation

Denault¹,

Wang²,

Cooks³

et al. 2000

J. Phys. Chem. A

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“…In analogy with proton transfer reactions, methyl cation transfer has an associated methyl cation affinity (MCA) defined as the negative A H 0 of Neither the rate constant for reaction [4] nor the MCA of SiO has yet been measured. However, using empirical rules developed by McMahon et al (27), one can say that for a base B of high PA (PA > 170 kcal mol-I), PA(B) -MCA(B) = 100 kcal mol-', giving a rough value of about 89 kcal mol-I for MCA(Si0). The MCA of CO is calculated to be 80 kcal mol-I (28-30).…”

Section: Positive Ion Chemistrymentioning

confidence: 99%

“…The MCA of CO is calculated to be 80 kcal mol-I (28-30). Using these numbers, reaction [4] should be exothermic by approximately 9 kcal mol-l. A rate constant for reaction [4] is not easy to estimate; methyl cation transfer reactions have very variable rate coefficients that are dependent on both the nature of the methyl cation receptor B and the exoergicity of the reaction (27). The results of…”

Section: Positive Ion Chemistrymentioning

confidence: 99%

Silicon cation and anion chemistry in a fuel-rich, methane–oxygen flame

Horton¹,

Goodings²

1992

Can. J. Chem.

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. Can. J. Chem. 70, 1069 (1 992). Silicon cations and anions in a fuel-rich, premixed, methane-oxygen flame at atmospheric pressure doped with 0.01 mol% of trimethylsilane were observed by sampling the flame through a nozzle into a mass spectrometer. Twelve cations were observed which can be grouped into five series: SiOH'.nH20 (n = 0-2); SiOCH3+.nH20 (n = 0-2); Si(OH)3'.nH20 (n = 0-2); cations by nucleophilic substitution (e.g., Si(OH)(CH3)2(H20)+); and carbonaceous aromatic cations (c-HS~CH=CH' and c-HSiCH=CCH,+). Similarly, five anions were observed as members of two series: H,Si03-(x = 0, I) and H,SiO,-(x = 1-3). The chemical ionization reactions for the formation of these ions are discussed in detail, including proton transfer and also methyl cation transfer, three-body addition, nucleophilic substitution (SN2) of both the ions themselves and also their neutral silicon precursors, and H-atom abstraction reactions. The neutral silicon chemistry in the flame is dominated by SiO, but evidence was obtained from both the cation and the anion chemistry for the presence of HSiO(OH), silanoic acid; SiO(OH)2, metasilicic acid; and Si(OH),, orthosilicic acid. The silicon ion chemistry differs markedly from the normal carbon ion chemistry that occurs naturally in the undoped methane-oxygen flame; the silicon ions show a strong tendency towards Si-0 bond formation. Consideration is given to the probable structures of the various silicon cations and anions observed. On a observe des anions et des cations silicies dans la flamme de primklange d'un melange de methane-oxygkne riche en methane la pression atmosphkrique et dope avec 0,1% de trimethylsilane, en injectant, a I'aide d'une buse, des Cchantillons de flamme dans un spectromktre de masse. On a observe 12 cations que l'on peut regrouper en cinq categories : SiOH' .n H 2 0 (n = 0-2); SiOCH,+.n H 2 0 ( n = 0-2); Si(OH),+ .n H 2 0 (n = 0-2); des cations obtenus par substitution nucleophile (par exemple : Si(OH)(CH3)2(HIO)'); et des cations carbones aromatiques (c-HS~CH=CH+ et c-HS~CH=CCH,'). D'une f a~o n analogue, on a observe cinq anions appartenant a deux series : H,Si03-(x = 0, 1); et H,SiO, (x = 1-3). On discute en dktail des rkactions d'ionisation chimique conduisant a ces ions. Ces riactions comprennent : le transfert de proton et de cation methyle, l'addition a trois espkces, la substitution nuclkophile (SN2) des deux anions eux-mCmes et de leur precurseur silicie et les reactions d'abstraction d'hydrogene. La chimie du silicium neutre, dans la flamme, est dominee par le SiO, mais on a obtenu des preuves de la presence de l'acide silanoique, HSiO(OH), de l'acide mktasilicique, SiO(OH),, et de l'acide orthosilicique, Si(OH),, a partir de la chimie des cations et des anions. La chimie du silicium differe nettement de la chimie d l'ion carbone normal qui se forme naturellement dans la flamme du melange methane-oxygene non dope; les ions silicium exhibent une forte tendance vers la formation de liaison Si-0. On formule des hypotheses sur les structures probables de...

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“…From the fundamental point of view, a first step is to investigate the still unexplored behavior of NF 3 as a bifunctional Lewis base when interacting with a neutral Lewis acid. Experimental and theoretical investigations on the ligation of NF 3 to ionic Lewis acids such as H ϩ , [23,24] Li ϩ , [25,26] CH 3 ϩ , [27,28] and NF 2 ϩ [29,30] clearly indicate that both the MϪNF 3 ϩ and MFϪNF 2 ϩ isomeric structures (M ϭ H, Li, CH 3 , and NF 2 ) can, in principle, exist as distinguishable species in the gas phase, and that the nature of the M ϩ electrophile has a substantial effect on both the relative stability of the two isomers and on the their energy difference. Conversely, experimental and theor-etical studies performed on complexes between NF 3 and neutral Lewis acids, such as BH 3 ,…”

Section: Introductionmentioning

confidence: 99%

Nitrogen Trifluoride as a Bifunctional Lewis Base: Implications for the Adsorption of NF₃ on Solid Surfaces

2004

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The structure, stability, and thermochemistry of isomeric adducts between NF 3 and the Lewis acids BH 3−n F n (n = 0−3) have been investigated at the coupled-cluster and at the Gaussian-3 (G3) level of theory. At the CCD/cc-pVDZ level both the nitrogen-and the fluorine-coordinated structures of all BH 3−n F n −(NF 3 ) (n = 0−3) adducts were characterized as true minima on the potential energy surface, thus providing the first theoretical evidence for the behavior of NF 3 as a bifunctional Lewis base when interacting with neutral Lewis acids. At the G3 level, and 298.15 K, including the contribution of the entropy term, the H 3 B−NF 3 adduct is predicted to be more stable than H 3 B−F−NF 2 by 4.3 kcal mol −1 ; this free energy difference is 3.7 kcal mol −1 at the CCSD(T)/ccpVTZ//CCD/cc-pVDZ level of theory. Conversely, at the lat-

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Methyl cation affinities

Cited by 107 publications

References 0 publications

Structural Characterization of Clusters Formed from Alkyl Nitriles and the Methyl Cation

Structural Characterization of Clusters Formed from Alkyl Nitriles and the Methyl Cation

Silicon cation and anion chemistry in a fuel-rich, methane–oxygen flame

Nitrogen Trifluoride as a Bifunctional Lewis Base: Implications for the Adsorption of NF₃ on Solid Surfaces

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Methyl cation affinities

Cited by 107 publications

References 0 publications

Structural Characterization of Clusters Formed from Alkyl Nitriles and the Methyl Cation

Structural Characterization of Clusters Formed from Alkyl Nitriles and the Methyl Cation

Silicon cation and anion chemistry in a fuel-rich, methane–oxygen flame

Nitrogen Trifluoride as a Bifunctional Lewis Base: Implications for the Adsorption of NF3 on Solid Surfaces

Contact Info

Product

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Nitrogen Trifluoride as a Bifunctional Lewis Base: Implications for the Adsorption of NF₃ on Solid Surfaces