1759-87-1Relevant academic research and scientific papers
Unimolecular Reactions of Isolated Organic Ions: the Chemistry of the Oxonium Ions CH3CH2CH2CH2(+)O=CH2 and CH3CH2CH2CH=O(+)CH3
Bowen, Richard D.,Derrick, Peter J.
, p. 1197 - 1209 (1993)
The reactions of the metastable oxonium ions CH3CH2CH2CH2(+)O=CH2 and CH3CH2CH2CH=O(+)CH3 are reported and discussed.Both these isomers of C5H11O(+) expel predominantly CH2O (75 - 90percent of the metastable ion current), a moderate amount of C3H6 (5-15percent), a minor amount of CH3OH (2-8percent) and a very small proportion of H2O (0.5-3percent).All these processes give rise to Gaussian metastable peaks.The kinetic energy releases associated with fragmentation of these oxonium ions are similar, but slightly larger for dissociation of CH3CH2CH2CH=O(+)CH3.The behaviour of labelled analogues confirms that the reactions of CH3CH2CH2CH2(+)O=CH2 and CH3CH2CH2CH=O(+)CH3 are closely related, but subtly different.Elimination of CH2O and C3H6 is intelligible by means of mechanisms involving CH3CH(+)CH2CH2OCH3.This open-chain cation is accessible to CH3CH2CH2CH2(+)O=CH2 by a 1,5-H shift and to CH3CH2CH2CH=O(+)CH3 by two consecutive 1,2-H shifts (or, possibly, a direct 1,3-H shift).The rates of these 1,2-, 1,3- and 1,5-H shifts are compared with one another and also with the rates of CH2O and C3H6 loss from each of the two oxonium ions.The 1,5-H shift that converts CH3CH(+)CH2CH2OCH3 formed from CH3CH2CH2CH=O(+)CH3 into CH3CH2CH2CH2(+)O=CH2 prior to CH2O elimination is essentially unidirectional.In contrast, the corresponding step converting C5H11O(+) ions generated as CH3CH2CH2CH2(+)O=CH2 into CH3CH(+)CH2CH2OCH3 competes effectively with expulsion of CH2O and C3H6.The implications of the latter finding for the degree of concert in the hydrogen transfer and carbon-carbon bond fission steps in alkene losses from oxonium ions via routes that are formally isoelectronic with the retro 'ene' pericyclic process are emphasized.
Kinetics an Stereochemistry of the Thermal Interconversion of 4,5-Dimethyl-2,6-octadienes
Gajewski, Joseph J.,Benner, Charles W.,Hawkins, Christopher M.
, p. 5198 - 5204 (1987)
Gas-phase pyrolysis of threo-4,5-dimethyl-cis,cis-1,1,1,8,8,8-hexadeuterio-2,6-octadiene over the temperature range 220.0-260.0 deg C resulted in formation of the threo, trans, trans isomer with log k = 11.36 - 36000/2.303RT.NMR analysis with Simplex minimization of the residuals from a Gear numerical integration provided a nearly identical rate constant for the degenerate interconversion of the deuterium isomers of the threo,trans,trans diastereomer at 240 deg C.All six 4,5-dimethyl-2,6-octadienes are interconverted at temperatures above 290 deg C.Mass spectral analysis of the reaction products from a 1:1 mixture of protio and D6 diene provided evidence for cleavage-recombination as the pathway for conversion to erythro,trans,trans,erythro,cis,cis and threo,trans,cis isomers.Competing with the cleavage-recombination is the boatlike shift to the erythro,trans,cis isomer.NMR analysis of the (-)-α-phenylethylamine bis salt of the threo-2,3-dimethylsuccinic acid derived from 33.5-h 240 deg C pyrolysis of optically pure hexadeuterio starting material provided evidence for little incursion of antarafacial-antarafacial 3,3-shifts via a twist transition state competing with the chair transition state.An analysis of the energy surface for all interconversions reveals that at 300 deg C, the boat transition state is ca. 6 kcal/mol higher in energy than the sterically most favorable chair transition state, and the cleavage reaction transition state is only 0.6 kcal/mol higher in energy than the boat transition state.
Mechanism of Propene and Water Elimination from the Oxonium Ion CH3CH=O+CH2CH2CH3
Bowen, Richard D.,Suh, Dennis,Terlouw, Johan K.
, p. 119 - 130 (1995)
The site-selectivity in the hydrogen transfer step(s) which result in propene and water loss from metastable oxonium ions generated as CH3CH=O+CH2CH2CH3 have been investigated by deuterium-labelling experiments.Propene elimination proceeds predominantly by transfer of a hydrogen atom from the initial propyl substituent to oxygen.However, the site-selectivity for this process is inconsistent with β-hydrogen transfer involving a four-centre transition state.The preference for apparent α- or γ-hydrogen transfer is interpreted by a mechanism in which the initial propyl cation accessible by stretching the appropriate bond in CH3CH=O+CH2CH2CH3 isomerizes unidirectionally to an isopropyl cation, which then undergoes proton abstraction from either methyl group +CH2CH2CH3 CH3CH=O---+CH2CH2CH3 +CH(CH3)2> + CH3CH=CH2>>.This mechanism involving ion-neutral complexes can be elaborated to accommodate the minor contribution of expulsion of propene containing hydrogen atoms originally located on the two-carbon chain.Water elimination resembles propene loss insofar as there is a strong preference for selecting the hydrogen atoms from the α- and γ-positions of the initial propyl group.The bulk of water loss is explicable by an extension of the mechanism for propene loss, with the result that one hydrogen atom is eventually transferred to oxygen from each of the two methyl groups in the complex +CH(CH3)2>.This site-selectivity is strikingly different from that (almost random participation of the seven hydrogen atoms of the propyl substituent) encountered in the corresponding fragmentation of the lower homologue CH2=O+CH2CH2CH3.This contrast is explained in terms of the differences in the relative energetics and associated rates of the cation rearrangement and hydrogen transfer steps.
Raman spectroscopy of n-pentyl methyl ether and deuterium labelledanalogues
Bowen, Richard D.,Edwards, Howell G. M.,Farwell, Dennis W.,Morgan, Sara E
, p. 1725 - 1734 (2010)
The Raman spectra of n-pentyl methyl ether, C5H 11OCH3, and six selectively deuteriated analogues arereported and discussed. Correlations between the observed ν(sp 3CH)stretching and bending bands and the position of the deuterium atoms in thealkyl chain are developed and refined. Similar progress is possible inassociating specific skeletal vibrations with bands in the Raman spectra. Therelevance of this study to improving the assignment of bands in the Ramanspectra of larger systems of biological interest is highlighted. Copyright
INTERMEDIATES IN COBALT-CATALYSED METHANOL HOMOLOGATION: LABELLING STUDIES WITH DEUTERATED METHANOL AND METHYL IODIDE
Roeper, Michael,Loevenich, Heinz
, p. 95 - 102 (1983)
The cobalt-catalysed homologation of perdeuterated methanol with CO/H2 gives C2 products in which the CD3 group remains intact.GC/MS measurements showed that no H/D exchange unless the methanol conversion exceeded 50percent.These results indicate that methylene species are unlikely to be as catalytic intermediates, and favour methyl species for such intermediates.In the presence of iodine promoters methyl iodide is a likely intermediate since it is much more readily consumed than methanol in carbonylation/hydrocarbonylation reactions.This was shown by treating a 5/1 mixture of CH3OH and CD3I with CO/H2 in the presence of Co2(CO)8; at short reaction times only the carbonylation/hydrocarbonylation products of methyl iodide could be detected by GC/MS.Methyl iodide can be formed from variety of iodine compounds under homologation conditions, as was confirmed by separate experiments.
Metastable Decompositions of C5H10O+. Ions with the Oxygen on the Middle Carbon: A Test for Energy Randomization
McAdoo, David J.,Farr, William,Hudson, Charles E.
, p. 5165 - 5169 (1980)
This study was undertaken to define the mechanisms of metastable decomposition of C5H10O+. ions with the oxygen on the middle carbon, and to test the assumption that internal energy becomes randomly distributed prior to the unimolecular decompositions of gaseous ions.CH3CH2C(=OH+)CH2CH2. (2), CH3CH2C(=OH+).CHCH3 (3), and CH3CH2C(OH+.)HCH=CH2 (4) all rearrange to CH3CH2C(=O+.)CH2CH3 (1) prior to metastable decomposition.However, 2 - 4 lose ethyl 50 - 100 times as often as they lose ethane following rearrangement to 1, while 1 formed by ionization of 3-pentanone loses exclusively ethane.These differences are attributed to excess energy in the isomerized ions. 3-Pentanone ions formed by isomerization of 2 - 4 lose ethyl and ethane from opposite sides at unequal rates, possibly owing to incomplete randomization of energy following isomerization.
SYNTHESIS AND NMR SPECTRA OF 2,2,2,-TRIDEUTERIOETHYLARSINE AND 2,2,2-TRIDEUTERIOETHYLCYCLOPENTAARSINE
Rheingold, A. L.,Natarajan, S.
, p. 119 - 124 (1982)
Pentakis(2,2,2-trideuterioethyl)cyclopentaarsine (PDECA) was synthesized by the reaction of 2,2,2-trideuterioethylarsine with dibenzylmercury.Variable temperature NMR spectra in C6D6 are interpreted in terms of fast pseudorotation.NMR and mass spectra and synthesis of 2,2,2-trideuterioethylarsine are also described.
A study of the gas-phase reactivity of neutral alkoxy radicals by mass spectrometry: α-Cleavages and Barton-type hydrogen migrations
Hornung, Georg,Schalley, Christoph A.,Dieterle, Martin,Schroeder, Detlef,Schwarz, Helmut
, p. 1866 - 1883 (1997)
The reactivity of neutral alkoxy radicals in the absence of any interfering intermolecular interactions is investigated by means of the recently introduced method of neutral and ion decomposition difference (NIDD) spectra. These are obtained from quantitative analysis of the corresponding neutralization - reionization (NR) and charge reversal (CR) mass spectra. The following trends emerge: alkoxy radicals with short (C1-C3) or branched alkyl chains give rise to α-cleavage products, whereas longer-chained alkoxy radicals undergo 1,5-hydrogen migrations from carbon to oxygen, that is, Barton-type chemistry. This facile rearrangement has been studied in detail for n-pentoxy radicals by isotopic labeling experiments and computation at the Becke 3LYP/6-31G* level of theory. Further, the NIDD spectra of 3-methylpentoxy radicals permit for the first time the identification of the diastereoselectivity of the gas-phase hydrogen migrations. The results from the NIDD method are compared to those from earlier studies in the condensed phase. This new mass spectrometric approach is suggested as a tool for the examination of intramolecular reactions of free alkoxy radicals which can usefully complement theoretical studies.
Unimolecular Reactions of Isolated Organic Ions: Reactions of the Immonium Ions CH2=N+(CH3)CH(CH3)2, CH2=N+(CH3)CH2CH2CH3 and CH2=N+(CH2CH2CH3)2
Bowen, Richard D.,Colburn, Alex W.,Derrick, Peter J.
, p. 2363 - 2372 (1993)
The reactions of metastable CH2=N+(CH3)C3H7 immonium ions have been investigated by means of 2H-labelling experiments and kinetic energy release measurements.Loss of C3H6, with specific β-H transfer, is the sole channel for dissociation of CH2=N+(CH3)CH(CH3)2.This process gives rise to a Gaussian metastable peak.The isomeric ion, CH2=N+(CH3)CH2CH2CH3, also expels C3H6; however, both α-H and γ-H as well as β-H transfer occurs in this case, and the reaction proceeds with an increased kinetic energy release.The role of ion-neutral complexes in C3H6 loss from CH2=N+(CH3)C3H7 ions is discussed.In addition, CH2=N+(CH3)CH2CH2CH3 eliminates C2H4.This fragmentation yields a broad dish-topped metastable peak, corresponding to a very large kinetic energy release (T1/2 ca. 73 kJ mol-1), and it involves specific and unidirectional γ-H transfer.A potential energy profile summarising the reactions of CH2=N+(CH3)CH2CH2CH3 and CH2=N+(CH3)CH(CH3)2 is constructed.The mechanisms by which immonium ions of this general class eliminate C3H6 and C2H4 have been further probed by studying the behaviour of the higher homologue, CH2=N+(CH2CH2CH3)2.The mechanistic conclusions derived from this work are found to be in excellent qualitative agreement with those of previous studies.
Deuteron Quadrupole Coupling Constants of the Methyl and Methylene Groups of Ethanol from the Direct 13C-2H and 2H-2H Couplings in 2H-NMR Spectra
Lickfield, G. C.,Beyerlein, A. L.,Savitsky, G. B.,Lewis, L. E.
, p. 3566 - 3570 (1984)
The deuteron quadrupole coupling constants, QD, of 13C(2)H3CH2OH and CH3(13)C2H2OH were measured in two different nematic solvents by employing the quadrupolar splitting and 13C-2H and 2H-2H dipolar splittings in 2H NMR spectra.In order to obtain the most accurate values for QD, vibrational averaging of the dipolar couplings and ab initio calculations of the C-D bond asymmetry correction were used in the theoretical treatment of the experimental data.The values found in ZLI-1167 are 186.6 and 178.2 kHz and in phase IV are 180.7 and 176.6 kHz for the methyl and methylene groups, respectively.Using the previously obtained 2H NMR relaxation data and the QD value determined in ZLI-1167, we calculated the internal rotation coefficient of the methyl group to be 0.68E11 s-1.
