61809-88-9Relevant academic research and scientific papers
Protonated 1,3,5-cycloheptatriene and 7-alkyl-1,3,5-cycloheptatrienes in the gas phase: Ring contraction to the isomeric alkylbenzenium ions
Mormann, Michael,Kuck, Dietmar
, p. 384 - 394 (2007/10/03)
1,3,5-Cycloheptatriene (1) and various 7-alkyl-1,3,5-cycloheptatrienes (3, 6, 9, 13, and 16-19) were subjected to gas-phase protonation under CI(CH4) and CI(iC4H10) conditions and the MIKE spectra of their [M + H]+ ions were measured. Loss of CH4 from the parent ion [1 + H]+ and almost exclusive loss of C2H4 from the methyl derivative [3 + H]+ indicate ring contraction of the dihydrotopylium ions to protonated toluene (toluenium ions) and protonated ethylbenzene (ethylbenzenium ions), respectively, prior to fragmentation. With increased exothermicity of protonation, ions [3 + H]+ also isomerize to xylenium ions. Similarly, higher protonated n-alkylcycloheptatrienes undergo skeletal isomerization to the corresponding 'chain-elongated' (n + 1)-alkylbenzenium and to the corresponding n-alkyltoluennium ions. Starting with ethyldihydrotropylium ions, a competing isomerization channel is opened giving rise to expulsion of C2H4 from the constituents of the seven-membered ring, as evidenced by deuterium labelling and an unusually high kinetic energy release. Isoalkyl analogues behave in a similar manner with increased hydrogen exchange between the α position of the side chain and the ring.
Side-chain Effects on the Fragmentation Behaviour of Alkylthiophenes
Lange, D.,Budzikiewicz, H.
, p. 432 - 438 (2007/10/02)
The processes leading to the fragment ions formed from alkylthiophene molecule ions by benzylic cleavage without and with transfer of one hydrogen from the side-chain to the ring and the influence of additional methyl groups on the relative importance of these two fragmentation reactions were investigated.
THE rs STRUCTURES OF PROPYL FLUORIDE AND DIFFERENCES IN STRUCTURES BETWEEN ROTATIONAL ISOMERS
Hayashi, Michiro,Fujitake, Masaharu
, p. 9 - 24 (2007/10/02)
Microwave spectra of trans and gauche propyl fluoride and its isotopically substituted species have been measured.The rs structures of the trans and gauche isomers of this molecule are determined from the observed moments of inertia.It is found that the CCC angle values are largely different between two isomers, while the CCF angle values stay unchanged.The rs structures of ethyl fluorosilane and ethylmethyl sulfide are re-examined in order to compare the results with those of propyl fluoride.The differences in the structural parameter values between the rotational isomers are discussed for the present molecules and the analogous molecules such as ethanethiol and ethaneselenol.
The Reactions of Metastable +. Ions with the Oxygen on the Second Carbon
McAdoo, David J.,Hudson, Charles E.,McLafferty, Fred W.,Parks, Terry E.
, p. 353 - 362 (2007/10/02)
Nearly all +.> isomers with the oxygen on the second carbon are shown to interconvert with each other and lose methyl and ethylene at the threshold for dissociation.The methyls contain the carbon from the 1- and 5-positions with about equal frequency, and C(3) or perhaps C(4) about half as often as either terminal carbon.CH3CH2CH2CO+ is formed by loss of the C(1) methyl and CH2=CHC(O+H)CH3 by loss of the C(5) methyl.Hydrogen transfer between C(5) and the oxygen and between the oxygen and C(4) are facile, and 1,2-hydrogen transfers between C(3) and C(4) occur with high frequency.Extensive skeletal rearrangements also take place by 1,2-shifts between C(2), C(3) and C(4).We attribute the occurence of the three-center shifts between C(2), C(3) and C(4) to the presence of considerable charge density on C(2) and C(3) in many of the +. isomers.The isomerizations of +. can be considered a mixture of free radical and carbocation reactions.Strong similarities exist between the isomerizations of metastable +. ions with the oxygen on the second carbon and those of isomers of ionized butanoic acid, methyl butanoate and n-butanal.
Pseudo One-Step Cleavage of C-C Bonds in the Decomposition of Ionized Carboxyclic Acids. Radical Like Reactions in Mass Spectrometry
Weiske, Thomas,Schwarz, Helmut
, p. 323 - 347 (2007/10/02)
Metastable molecular ions of hexanoic acid (1) decompose unimolecularly to C2H5. and protonated methacrylic acid (5-H+)(92percent rel. abund.).Investigation of the mechanism reveals that 1) the branched cation radical 11 must be regarded as the essential intermediate in the course of the rearrangement/dissociation reaction and 2) the process commences with intramolecular hydrogen transfer from either C-3 or C-5 to the ionized carbonyl oxygen ("hidden" hydrogen migration).Hydrogen transfer from C-4, which would correspond to the well-known McLafferty rearrangement, is of no importance in the C2H5.-elimination from 1.The same conclusion applies for various alternative mechanisms, as for example a SRi type reaction, 1 -> 2-H+.The gas phase chemistry of the cation radical of 1, and in particular the hydrogen exchange processes between the methylene groups C-2/C-3 and C-5/C-6, is in surprisingly close correspondence to the chemistry of free alkyl radicals. - The syntheses of various 13C and 2H-labelled model compounds are described.
