Isomeric distonic and H-bridged [C2H6O]+ radical cations

Postma, R.; Ruttink, P.J.A.; Baar, Ben van; Terlouw, Johan K.; Holmes, John L.; Burgers, Peter C.

doi:10.1016/0009-2614(86)80033-1

Cited by 56 publications

(11 citation statements)

References 20 publications

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“…However, the labelling data show that this isomerisation occurs at most for 10% of the original propane radical-cations. Therefore, in contrast to the relatively unrestricted freedom of movement of the partners in some other complexes, 12,58 the methyl radical does not migrate freely around the ethyl cation in the complex in methane loss from ionised propane. Instead, the isomerisation and direction of motion of the methyl radical are coordinated, perhaps because less energy is required to reach the transition state for simple 1,2-elimination of methane than is needed for isomerisation or complete detachment of the methyl radical.…”

mentioning

confidence: 83%

EMS Account: Alkane eliminations from ions in the gas phase

McAdoo

Bowen

1999

Eur. J. Mass Spectrom.

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A review of reactions involving the elimination of an alkane from a variety of even and odd electron ions in the gas phase is presented. Particular attention is focused on the mechanisms of these reactions and the role of ion-neutral complexes. Alkane eliminations from open shell species derived by ionisation of ketones, ethers, alcohols, amines, alkanes and alkyl-substituted cycloalkanes are considered, together with ethane loss from the distonic ion CH 2 =O + CH 2 CH 2 •. These reactions are, without obvious exception, complex-mediated. Elimination of alkanes from an assortment of closed shell ions, including protonated acetaldehyde, dialkylmethylene immonium ions, onium ions, quaternary ammonium cations, alkoxide anions, enolate anions and deprotonated amines are also discussed. These reactions tend to be complex-mediated when heterolytic bond cleavages are possible. When such cleavages are not energetically feasible, alkane eliminations can take place by asynchronous, concerted mechanisms. Several factors affect the relative rates of alkane elimination compared to those of competing alkyl radical loss in the dissociations of these radical-cations; these factors include the internal energy of the ion, the size of the ionic and neutral partners, the initial orientation of these components and the binding energy of the complex. In addition, primary and secondary isotope effects influence both alkyl radical and alkane elimination. When alkanes are eliminated from radical-cations, reaction between the partners is often quickly overtaken in importance by direct separation of the components if the internal energy is raised either by increasing the energy of the ionisation process or by prior isomerisation over an energy barrier. This trend demonstrates that the attractions between the partners are easily overcome by quite small amounts of excess energy in the system. Typical binding energies between the ionic and non-polar neutral partners lie in the range 0-30 kJ mol-1 at distances at which covalent forces cease to be significant. Illustrative examples are given to show how studies of reactions involving ion-neutral complexes offer a means of obtaining information on the dynamics of short range interactions between ions and neutrals, including the motions of the partners relative to each other.

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mentioning

confidence: 83%

EMS Account: Alkane eliminations from ions in the gas phase

McAdoo

Bowen

1999

Eur. J. Mass Spectrom.

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“…The binding energy between the partners in 10, the immediate precursor of 7, should be similar to that in [CH,CHOH HOCH3]+', about 84 kJ m~l -' , ,~ and [CH,=CH:' H,O], 70 kJ mol-'. 26 The binding energy places the threshold for the formation of 10 at 5;!8-542 kJ mol-', -40-25 kJ mol-' below the threshold for the simple dissociation 8 + 13 of 567 kJ mol-' (Fig. 2).…”

Section: The Species That Loses H and Chmentioning

confidence: 97%

Formation of CH₃CH₂OCH₃^+˙ and ^˙CH₂⁺OHCH₂CH₃ from ionized 2‐ethoxyethanol and theoretical and experimental studies of the reactions of ^˙CH₂⁺OHCH₂CH₃

McAdoo

Ramanujam

George

1993

Org. Mass Spectrom.

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It is concluded that C3H80+' formed by dissociation of ionized 2ethoxyethanol (8) is a mixture of CH,CH,OCHl' (7) and 'GH,+OHCH,CH, (2). Formation of 7 and CH3CH2+0HCH3 (12) is attributed to dissociations of species formed by the hydrogen transfers [ CH,CH20CH2+ 'CH,OHI + [CH,CH,OCHi' CH,Ol -+ [CH,CH,+OHCH, HCO]. Production of 7 competes weakly with dissociation to CH,CH,+OCH, (13) and to 12. The low abundance of 7 is attributed to the simple dissociation 8 + 13 being both energetically and entropically favored, and a second H-transfer to give 12 being energetically favored. The threshold for forming 7 is 45 kJ mol-' above that for dissociation directly to 13, so formation of 7 is the first ion-neutral complex-mediated elimination found to have a threshold above that for the competing simple dissociation. The low abundance of 7 also demonstrates that ion-neutral complexes can be intermediates without obviously revealing their presence by direct dissociation. Experimental results suggest that 2 isomerizes to CH,CH2CHz0H+' (5) and then dissociates by eliminating water. Ab initio results support the feasibility of 2 + CH,+OHCH,CH,' (1) and 2 + 5. However, experimental observations suggest that 2 + 1 does not occur. This is attributed to strong competition from dissociation and isomerization to 5. The transition state for 2 + 5 resembles [ CH,CH, CH,OHI +., and a cyclic transition state for 2 + 5 is ruled out. When the ethyl-oxygen bond in 2 is simply lengthened, the charge is initially concentrated on ethyl, but it switches to CH,OH in a curve crossing at an apparent transition state for C -0 bond breaking. 45

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“…Two examples are the demonstration that enol ions are thermodynamically more stable than their keto counterparts, (the reverse of neutral behavior), and that distonic ions, in spite of their unconventional structures (at least in comparison with their neutral counterparts which are diradicals) are often more stable than their isomers of conventional structure. Thus Holmes and co-workers illustrated the first point for ketones, aldehydes, carboxylic acids, and esters (Holmes, Terlouw, & Lossing, 1976;Holmes & Lossing, 1979;Holmes & Lossing, 1980a,b) and the second followed the experimental identification of the ion CH 2 CH 2 OH 2 eþ , originally identified as an ion-dipole complex (Terlouw, Heerma, & Dijkstra, 1981) and later shown to be more stable than ionized ethanol or dimethylether by some 30-40 kJ/mol (Postma et al, 1986). The first production of the simpler distonic ion CH 2 OH 2 eþ was reported in 1982 (Bouma, McLeod, & Radom, 1982;.…”

Section: Neutral and Ion Thermochemistrymentioning

confidence: 99%

Neutral and ion thermochemistry: Its present status and significance

Holmes

Aubry

2009

Mass Spectrometry Reviews

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This short account outlines the sources of thermochemical data that are important for gas phase ion chemistry. It describes some of the relationships that have been identified for the empirical estimation of enthalpies among neutral molecules, free radicals, and odd and even electron ions. For neutral species, the additivity principle works well and this has been developed to cover a very wide range of structures and isomers. Ionization energies of homologous species depend inversely on molecular size, allowing estimates to be made for missing members. For ions, the effect of a group substitution (such as replacing a hydrogen atom by, e.g., a methyl or hydroxyl group) can easily be estimated, but such results are strongly dependent upon the position of the charge site, relative to that of the substitution. Special emphasis is given to the reliability of data collections and simple directions are provided as to how critically to assess and identify less-than-satisfactory values.

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Isomeric distonic and H-bridged [C2H6O]+ radical cations

Cited by 56 publications

References 20 publications

EMS Account: Alkane eliminations from ions in the gas phase

EMS Account: Alkane eliminations from ions in the gas phase

Formation of CH₃CH₂OCH₃^+˙ and ^˙CH₂⁺OHCH₂CH₃ from ionized 2‐ethoxyethanol and theoretical and experimental studies of the reactions of ^˙CH₂⁺OHCH₂CH₃

Neutral and ion thermochemistry: Its present status and significance

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Isomeric distonic and H-bridged [C2H6O]+ radical cations

Cited by 56 publications

References 20 publications

EMS Account: Alkane eliminations from ions in the gas phase

EMS Account: Alkane eliminations from ions in the gas phase

Formation of CH3CH2OCH3+˙ and ˙CH2+OHCH2CH3 from ionized 2‐ethoxyethanol and theoretical and experimental studies of the reactions of ˙CH2+OHCH2CH3

Neutral and ion thermochemistry: Its present status and significance

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Formation of CH₃CH₂OCH₃^+˙ and ^˙CH₂⁺OHCH₂CH₃ from ionized 2‐ethoxyethanol and theoretical and experimental studies of the reactions of ^˙CH₂⁺OHCH₂CH₃