106,065 research outputs found
The activation energy of the skeletal isomerization in the radical cations of toluene and cycloheptatriene by mass spectrometry of their 2-phenylethyl derivatives
No full textKuck D, Grützmacher H-F. The activation energy of the skeletal isomerization in the radical cations of toluene and cycloheptatriene by mass spectrometry of their 2-phenylethyl derivatives. Organic Mass Spectrometry. 1979;14(2):86-97
Substituent Effects on the Intramolecular Proton Transfer in [omega]-Phenylalkylbenzenium Ions
No full textBäther W, Kuck D, Grützmacher H-F. Substituent Effects on the Intramolecular Proton Transfer in [omega]-Phenylalkylbenzenium Ions. Organic Mass Spectrometry. 1985;20(9):589-591
Gas-Phase Protonation of Diphenylalkanes
No full textCrestoni ME, Fornarini S, Kuck D. Gas-Phase Protonation of Diphenylalkanes. Journal of Physical Chemistry. 1995;99(10):3150-3155.The gas-phase protonation of alpha,omega-diphenylalkanes ranging from diphenylmethane to 1,6-diphenylhexane and of 1-phenyl-2-(m-tolyl)ethane has been examined by FT-ICR mass spectrometry. Their gas-phase basicities (GB) at 300 K are consistently higher than that of toluene, as expected from their higher polarizability, and depend on the length of the methylene chain joining the two phenyl groups. This noticeable structure dependence is ascribed to an intramolecular solvation effect exerted by the second phenyl ring on the protonated one, allowed by a proper conformation of the linking chain. This effect is confirmed by a ca. 2 kcal mol(-1) decrease in basicity when the protonated and the neutral phenyl rings are separated by the same number of C-C bonds in a rigid trans-cyclohexane-1,4-diyl unit versus a flexible chain
Interannular proton exchange in protonated long-chain 1, [omega]-diphenylalkanes
No full textKuck D, Bäther W, Grützmacher H-F. Interannular proton exchange in protonated long-chain 1, [omega]-diphenylalkanes. International Journal of Mass Spectrometry and Ion Processes. 1985;67(1):75-91
Internal Solvation Effects on the Reactivity of alpha,omega-Diphenylalkanes toward ME(3)C(+) Ions
No full textCrestoni ME, Fornarini S, Kuck D. Internal Solvation Effects on the Reactivity of alpha,omega-Diphenylalkanes toward ME(3)C(+) Ions. Journal of Physical Chemistry. 1995;99(10):3144-3149.The reactivity of alpha,omega-diphenylalkanes (1 less than or equal to n less than or equal to 4) toward Me(3)C(+) ions has been investigated with the radiolytic technique at 720 Torr, at temperatures of 47 and 120 degrees C. The intramolecular isotopic discrimination of Me(3)C(+), favoring attack at the unlabeled ring of C6H5(CH2)(2)C6D5 by a factor of 1.5 at 120 degrees C, contrasts with the lack of intermolecular isotopic discrimination, reflected by the same reactivity toward (C6H5CH2)(2) and (C6D5CH2)(2). Competition experiments show an appreciably higher reactivity of Ph(CH2)(n)Ph (n = 2-4) relative to toluene and diphenylmethane (DPM), but, when Ph(CH2)(n)Ph (n = 3, 4) or (3-CH3C6H4)(CH2)(2)C6H5 compete with Ph(CH2)(2)Ph, relative reactivities level off. The lack of substrate selectivity, in contrast to an intramolecular discrimination in the tert-butylation of (3-CH3C6H4)(CH2)(2)C6H5 of a factor of 2, together with the related variation of kinetic isotope effects, points out the kinetic role of the collision complex 1 from Me(3)C(+) and diphenylalkanes. The additional (''spectator'') ring of the higher homologues Ph(CH2)(n)Ph (n = 2-4) prevents dissociation of 1, making its formation irreversible and causing tert-butylation to occur at the encounter rate, in contrast to DPM, whose second ring appears essentially inert. Experiments involving substitution by Me(3)Si(+) at 120 degrees C show that this electrophile attacks preferably the unlabeled ring of C6H5(CH2)(2)C6D5 by a factor of 1.5, consistent with the 1.4 times higher reactivity toward (C6H5CH2)(2) With respect to (C6D5CH2)(2). In this case, the isotopic discrimination is traced to the competition between desilylation and deprotonation of intermediate ipso-silylated arenium ions
Gaseous [M - H]+ ions of alpha,omega-diphenylalkanes: cyclization to [M + H]+ type ions of benzocycloalkanes as recognized by chain-length dependent proton exchange
No full textKuck D. Gaseous [M - H]+ ions of alpha,omega-diphenylalkanes: cyclization to [M + H]+ type ions of benzocycloalkanes as recognized by chain-length dependent proton exchange. International Journal of Mass Spectrometry and Ion Processes. 1992;117(1-3):441-455.Metastable [M - H]+ ions of alpha,omega-diphenylalkanes C6H5(CH2)xC6H5 where x = 3-6 (structures 3-6 respectively), generated by hydride abstraction in the chemical ionization (i-butane) source, eliminate benzene after proton exchange between the aromatic rings. The proton exchange is slow for ions [3 - H]+ and [4 - H]+, but fast and apparently complete for ions [5 - H]+ and [6 - H]+. These observations, combined with collision activation experiments, suggest the cyclization of the [M - H]+ ions to isomeric protonated 1-phenylbenzocycloalkane and 1-benzylbenzocycloalkane derivatives, i.e. to [M1 + H]+ type ions, with a preference for protonated tetralin structures. Hydrogen exchange between the aliphatic chain and the rings is absent or negligible for [M - H]+ ions of 3-5 but is significant for ions [6 - H]+
Mass spectrometry of alkylbenzenes and related compounds. Part II. Gas phase ion chemistry of protonated alkylbenzenes (alkylbenzenium ions)
No full textKuck D. Mass spectrometry of alkylbenzenes and related compounds. Part II. Gas phase ion chemistry of protonated alkylbenzenes (alkylbenzenium ions). Mass Spectrometry Reviews. 1990;9(6):583-630
Inter- and intra-annular proton exchange in gaseous benzylbenzenium ions (protonated diphenylmethane)
No full textKuck D, Bäther W. Inter- and intra-annular proton exchange in gaseous benzylbenzenium ions (protonated diphenylmethane). Organic Mass Spectrometry. 1986;21(8):451-457.Two distinct proton exchange reactions occur in metastable gaseous benzylbenzenium ions, generated by isobutane chemical ionization of diphenylmethane and four deuterium-labelled analogues. Whereas the proton ring-walk at the benzenium moiety is fast giving rise to a completely random intraannular proton exchange, the interannular proton exchange is surprisingly slow and competes with the elimination of benzene. A kinetic isotope effect of kH/kD= 5 has been determined for the interannular proton transfer, and a particularly high energy barrier of 50-75 kJ mol-1 has been estimated. These observations are attributed to steric restrictions of the ring-to-ring proton transfer in benzylbenzenium ions and contrasted to the fast interannular proton exchange in the higher homologues
Mass spectrometry of alkylbenzenes and related compounds. Part I. Gas-phase ion chemistry of alkylbenzene radical cations
No full textKuck D. Mass spectrometry of alkylbenzenes and related compounds. Part I. Gas-phase ion chemistry of alkylbenzene radical cations. Mass Spectrometry Reviews. 1990;9(2):187-233
Ion/neutral complexes generated during unimolecular fragmentation: Intra-complex hydride abstraction by tert-butyl cations from electron-rich and electron-poor 1,3-diphenylpropanes
No full textMatthias C, Cartoni A, Kuck D. Ion/neutral complexes generated during unimolecular fragmentation: Intra-complex hydride abstraction by tert-butyl cations from electron-rich and electron-poor 1,3-diphenylpropanes. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY. 2006;255-256:195-212.The hydride transfer and proton transfer occurring between the constituents of ion/neutral complexes of tert-butyl cations and electron-rich and electron-poor 1,3-diphenylpropanes, [(CH3)(3)C+ C6H5CH2CH2CH2C6H4X] were investigated by use of CI/MIKE spectrometry of nine 1-(tert-butylphenyl)-3-arylpropanes and 16 site-specific deuterium-labeled isotopomers. The competition between H- abstraction by the (CH3)(3)C+ ion from the neutral arene and H+ transfer to it was found to be strongly affected by the electron-donating substituents, in particular by X = OCH3, on the one hand, and X = F and CF3, on the other, suggesting that the 1,3-diphenylpropane molecule within the I/N complex acts and reacts as a bidentate solvating partner to the carbocation. The effect of the substituents X on the regioselectivity of the intra-complex hydride abstraction from the two benzylic CH2 groups, k(gamma-H)/k(alpha-H), and their influence on the kinetic isotope effect (k(H)/k(D))(gamma), operating during the abstraction from the substituted benzylic moiety, were determined in a semi-quantitative approach by assuming (k(H)/k(D))(alpha) = 1.60, the generally observed value for the unsubstituted benzylic moiety. The regioselectivity range was found to span almost three orders of magnitude, from k(gamma-H)/k(alpha-H) >= 11.2 for the complex [(CH3)(3)C+ (C6H5CH2CH2CH2C6H4)-H-alpha-H-gamma(p-OCH3)] to k(gamma-H)/k(alpha-H) <= 0.04 for the complex [(CH3)(3)C+ (C6H5CH2CH2CH2C6H4)-H-alpha-H-gamma(p-CF3)]. (C) 2006 Elsevier B.V. All rights reserved
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