1759-87-1Relevant articles and documents
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.
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.
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.
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.
Alkene Loss from Metastable Methyleneimmonium Ions: Unusual Inverse Secondary Isotope Effect in Ion-Neutral Complex Intermediate Fragmentations
Veith, Hans J.,Gross, Juergen H.
, p. 1097 - 1108 (1991)
The mechanism of propene elimination from metastable methyleneimmonium ions is discussed.The first field-free region fragmentations of complete sets of isotopically labelled methyleneimmonium ions (H2C=N+R1R2 : R1 = R2 = n-C3H7; R1 = R2 = i-C3H7; R1 = n-C3H7; R2 = C2H5; R1 = n-C3H7; R2 = CH3; R1 = n-C3H7; R2 = H) were used to support the mechanism presented.The relative amounts of H/D transferred are quantitatively correlated to two distinct mathematical concepts which allow information to be deduced about influences on reaction pathways that cannot be measured directly.Propene loss from the ions examined proceeds via ion-neutral complex intermediates.For the di-n-propyl species rate-determining and H/D distribution-determining steps are clearly distinct.Whereas the former corresponds to a 1,2-hydride shift in a 1-propyl cation coordinated to an imine moiety, the latter is equivalent to a proton transfer to the imine occurring from the 2-propyl cation generated by the previous step.For the diisopropyl-substituted ions which directly form the 2-propyl cation-containing complex, the rate-determining hydride shift vanishes.The 2-propyl cation-containing complex can decompose directly or via an intermediate proton-bridged complex.Competition of these routes is not excluded by the experimental results.Assuming a 2:1:3 distribution, a preference for the α- and β-methylene of the initial n-propyl chain as the source of the hydrogen transferred is detected for n-propylimmonium ions containing a second alkyl chain R2.This preference shows a clear dependence on the steric influence of R2.During the transfer step isotopic substitution is found to affect the H/D distribution strongly.For the alternative route of McLafferty rearrangement leading to C2H4 loss, specific γ-H transfer is observed.
Nickel-Mediated Stepwise Transformation of CO to Acetaldehyde and Ethanol
Zhang, Ailing,Raje, Sakthi,Liu, Jianguo,Li, Xiaoyan,Angamuthu, Raja,Tung, Chen-Ho,Wang, Wenguang
, p. 3135 - 3141 (2017/09/05)
The insertion of CO into the Ni-C bond of synthetic Ni(II)-CH3 cationic complex ([1-CH3]+) affords a nickel-acetyl complex ([1-COCH3]+). Reduction of resultant [1-COCH3]+ by borohydrides produces CH3CHO, CH3CH2OH, and an Ni(0) compound ([1]0), which can react with CH3I to regenerate [1-CH3]+. By conducting deuterium labeling experiments, we have demonstrated that CH3CHO is the primary product from CH3CH2OH in such CO transformation reactions. In the reduction of [1-COCH3]+, the formation of CH3CHO competes with the loss of CH4, which leads to a Ni(0)-CO compound ([1-CO]0) as a minor product. Our results establish fundamental steps in the exploration of nickel-mediated CO transformation to valuable chemicals.
Intermediacy of ion neutral complexes in the fragmentation of short-chain dialkyl sulfides
Filsak,Budzikiewicz
, p. 601 - 610 (2007/10/03)
The main fragmentation processes after electron ionization of butyl methyl and butyl ethyl sulfides are rationalized by the intermediacy of the ion neutral complex [RSH · methylcyclopropane](+·) as demonstrated by extensive labeling and collision activation studies.
