61844-01-7Relevant articles and documents
Mechanistic Insights into Electroreductive C-C Coupling between CO and Acetaldehyde into Multicarbon Products
Chang, Xiaoxia,Malkani, Arnav,Xu, Bingjun,Yang, Xuan
, p. 2975 - 2983 (2020/03/10)
Production of valuable multicarbon (C3+) products through the electrochemical CO2 and CO reduction reactions (CO2RR and CORR) is desirable; however, mechanistic understanding that enables C-C coupling beyond the self-coupling of CO to valuable products is lacking. In this work, we elucidate the C-C coupling mechanism between CO and acetaldehyde, a reactive intermediate in both CO2RR and CORR, via combined isotopic labeling and in situ spectroscopic investigations. CO attacks the carbonyl carbon of acetaldehyde in the coupling, and the carbon in CO ends up in the hydroxymethyl group (-CH2OH) of the produced 1-propanol. While the coupling between CO and acetaldehyde does occur when the CORR is conducted with added acetaldehyde, only a minor fraction (up to 36%) of 1-propanol is from this pathway, and the majority of it is produced in the CORR by the self-coupling among CO. The adsorbed methylcarbonyl is proposed as the likely intermediate where the reaction pathway bifurcates to C2 and C3 products; i.e., it could either be hydrogenated to acetaldehyde and ethanol or couple with CO leading to the formation of 1-propanol.
Inherent asymmetry of constitutionally equivalent methyl groups in the H/D equilibration of n- and i-C3H7Fe(OH)+ complexes
Trage, Claudia,Zummack, Waltraud,Schroeder, Detlef,Schwarz, Helmut
, p. 2708 - 2710 (2007/10/03)
Transiently formed, constitutionally identical methyl groups remain inequivalent in the course of an n-propyl?isopropyl isomerization (see scheme) operative in Fe÷-mediated dehydration of propanols. The reversibility of the β-hydrogen transfer steps is addressed by examination of the H/D equilibration in metastable complexes of Fe+ with a set of selectivity deuterated propanols by using tandem mass spectrometry.
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.
Mechanism of Propene and Water Elimination from the Oxonium Ion CH3CH=O+CH2CH2CH3
Bowen, Richard D.,Suh, Dennis,Terlouw, Johan K.
, p. 119 - 130 (2007/10/02)
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.
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 (2007/10/02)
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.
The Mechanism of Water Loss from the Oxonium Ions CH3CH2CH2+ O=CH2 and (CH3)2CH+ O=CH2
Bowen, Richard D.,Colburn, Alex W.,Derrick, Peter J.
, p. 147 - 151 (2007/10/02)
Extensive new 2H-labelling results are reported, which pertain to the mechanism of water expulsion from metastable CH3CH2CH2+ O=CH2 and (CH)2CH+ O=CH2 ions.Detailed mechanisms, involving ion-neutral complexes comprising incipient propyl cations coordinated to formaldehyde, propene attached to protonated formaldehyde, or propene and formaldehyde attached to a common proton, are discussed in the light of the labelling data.Loss of positional integrity of the hydrogen and deuterium atoms within the original propyl groups occurs; it is proposed that this takes place via interconversion of the ion-neutral complexes.The crucial step in water elimination appears to be irreversible reorganization of the proton-bound complex (or an ion-neutral complex of protonated formaldehyde and propene) to the open-chain carbonium ion CH3+CHCH2CH2OH.
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.
