Letter to the editor

Schaldach, Bernd; Grützmacher, Hans‐Friedrich

doi:10.1002/oms.1210150314

Cited by 20 publications

(3 citation statements)

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“…The relative intensities of these peaks were variable from sample to sample and may be attributed to artifacts from the dissociation of ions in the field-free region prior to the magnetic sector. Such artifacts are commonly observed in MIKE spectra 10a, and details of these artifacts are discussed below. Product ions resulting from bond cleavages in the diaminopropane portion of the N -glycoside ligand were not detected.…”

Section: Resultsmentioning

confidence: 97%

Mechanistic Studies of Diastereomeric Nickel(II)N-Glycoside Complexes Using Tandem Mass Spectrometry

and

Leary

1998

J. Am. Chem. Soc.

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Ni(II) N-glycoside complexes of four diastereomeric monosaccharides were synthesized and analyzed by fast atom bombardment-mass spectrometry. The average kinetic energy release (KER) associated with the formation of a C 2 H 4 O 2 neutral loss was indicative of stereochemical differences in the coordinated monosaccharide. Isotopic labeling studies and various linked scanning techniques were undertaken, suggesting multiple dissociation pathways from different reacting configurations, leading to the formation of isomeric [M-C 2 H 4 O 2 ] product ions. Additionally, computational studies predict the presence of large structural differences between complexes possessing axial or equatorial C-2 substituents.

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Section: Resultsmentioning

confidence: 97%

Mechanistic Studies of Diastereomeric Nickel(II)N-Glycoside Complexes Using Tandem Mass Spectrometry

and

Leary

1998

J. Am. Chem. Soc.

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“…13 The first 0 C step determines the activation energy by the formation of a cyclic intermediate a with sufficient excitation energy to break the (C-X) bond in the second step. In the case of m-and p-chlorobenzalacetone, it has been proposed'2 that several 1,2-H or 1,3-H migrations follow the cyclization step until the intermediate b' has rearranged into a reactive configuration b (Scheme 5).…”

Section: Ch=ch-c-ch3mentioning

confidence: 99%

Kinetic and thermodynamic effects on intramolecular aromatic substitution in meta and para substituted benzalacetones

Schaldach

Grotemeyer

et al. 1981

Org. Mass Spectrom.

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meta and para substituted benzalacetones lose the substituents after electron impact in a multi-step intramolecular aromatic substitution. The differences in the relative abundances of the benzopyrylium ions thus formed are not determined by the activation energies for the substituent losses but depend on a delicate balance between the thermodynamic stability of the intermediates involved and the rates of several H-shifts within the intermediates (kinetic stability). The consequences for the analytical utility of intramolecular aromatic substitution are discussed brietly.

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“…According to Miller's quantification3 of the Hammond postulate" the position X;S of the transition state of an elementary reaction on the reaction coordinate can be expressed by the barrier height U* (here ~h f ) and potential energy of the reaction U, (here AH&) according to Eqn (6).…”

Section: Kinetic Energy Release and Energy Partitioningmentioning

confidence: 99%

Kinetic energy release and position of transition state during the intramolecular substitution of ionized 2‐benzoyl pyridines

Schubert

Grützmacher

1980

Org. Mass Spectrom.

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The loss of substituents X from molecular ions of ortho substituted 2-benzoyl pyridines has been investigated as a function of the dissociation energy of the C-X bond. Comparison of unimolecular and collisional induced decompositions of the resulting [M-XI' ions and reference ions arising from 3-hydroxypyrido[l,2-alindole shows that cyclic fragment ions are formed in every case by an intramolecular substitution reaction with the exception of the parent compound (X=H), which gives rise to a mixture of [M-HI' ions with different structures. The heat of formation of the cyclic ion has been estimated experimentally and by calculation using thennochemical data, and from this value and the appearance energies, the activation energies of the reverse reactions have been evaluated for the different reaction systems. Measurement of the kinetic energy release during the substitution readions shows that only part of the reverse activation energy is released as kinetic energy. The energy partitioning quotient varies from 0.37 to 0.08 depending on the dissociation energy of the C-X bond or the reaction enthalpy. A sudden change in the energy partitioning quotient is observed with increasing exothermicity of the reaction, paralleling the behaviour of similar reaction systems. These results are interpreted as a demonstration of the influence of the variation of transition state position on the energy partitioning quotient.It has been shown recently2 that the partitioning of the excess potential energy of the transition states (or the activation energy of the reverse reactions F:) between the kinetic energy T, released during the reaction, and the internal energy F * of the products during the loss of ortho substituents from the molecular ions of substituted benz.alacetones depends strongly and systematically on the thermochemistry of the reaction or the position3 of the transition state on the reaction coordinate. Thus it appears that an investigation of the variation of the kinetic energy release and the energy partitioning quotient q = T/&f with structural changes of the reactant ions gives some insight into fundamental properties of elementary reactions of organic ions, which will be useful in testing mechanistic models of organic chemistry and linking them more closely to physical theories of chemical reactions. The loss of substituents from molecular ions of benzalacetones with formation of 2-rnethylbenzpyrylium ions4 can be regarded as an intramolecular aromatic substitution reaction,5 a well known reaction in organic chemistry. As a further example of this type of reaction the results of a detailed investigation of the loss of ortho substituents from the molecular ions of substituted 2-benzoyl pyridines la-lg (Scheme 1) are reported.

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Letter to the editor

Cited by 20 publications

References 1 publication

Mechanistic Studies of Diastereomeric Nickel(II)N-Glycoside Complexes Using Tandem Mass Spectrometry

Mechanistic Studies of Diastereomeric Nickel(II)N-Glycoside Complexes Using Tandem Mass Spectrometry

Kinetic and thermodynamic effects on intramolecular aromatic substitution in meta and para substituted benzalacetones

Kinetic energy release and position of transition state during the intramolecular substitution of ionized 2‐benzoyl pyridines

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