Electronic structure of the six-membered cyclic transition state in some .gamma.-hydrogen rearrangements

Boer, F. P.; Shannon, T. W.; McLafferty, Fred W.

doi:10.1021/ja01028a012

Cited by 83 publications

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“…Two contradictory studies appeared in 1968. Hence, using nonempirical MO calculations, Boer et al 10 suggested a stepwise mechanism for the McLafferty rearrangement of the 2-pentanone radical cation, while Dougherty 11 argued that this type of reaction is electrocyclic, thus proceeding through a concerted transition structure (TS).…”

Section: Introductionmentioning

confidence: 99%

McLafferty rearrangement of the radical cations of butanal and 3‐fluorobutanal: A theoretical investigation of the concerted and stepwise mechanisms

Norberg

Salhi-Benachenhou

2007

J Comput Chem

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The stepwise and concerted pathways for the McLafferty rearrangement of the radical cations of butanal (Bu(+)) and 3-fluorobutanal (3F-Bu(+)) are investigated with density functional theory (DFT) and ab initio methods in conjunction with the 6-311+G(d,p) basis set. A concerted transition structure (TS) for Bu(+), (H), is located with a Gibbs barrier height of 37.7 kcal/mol as computed with CCSD(T)//BHandHLYP. Three pathways for the stepwise rearrangement of Bu(+) have been located, which are all found to involve different complexes. The barrier height for the H(gamma) transfer is found to be 2.2 kcal/mol, while the two most favorable TSs for the C(alpha)-C(beta) cleavage are located 8.9 and 9.2 kcal/mol higher. The energies of the 3F-Bu(+) system have been calculated with the promising hybrid meta-GGA MPWKCIS1K functional of DFT. Interestingly, the fluorine substitution yields a barrier height of only 20.5 kcal/mol for the concerted TS, (3F-H). A smaller computed dipole moment, 12.1 D, for (3F-H) compared with 103.2 D for (H) might explain the stabilization of the substituted TS. The H(gamma) transfer, with a barrier height of 4.9 kcal/mol, is found to be rate-determining for the stepwise McLafferty rearrangement of 3F-Bu(+), in contrast to the unsubstituted case. By inspection of the spin and charge distributions of the stationary points, it is noted that the bond cleavages in the concerted rearrangements are mainly of heterolytic nature, while those in the stepwise channels are found to be homolytic.

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Section: Introductionmentioning

confidence: 99%

McLafferty rearrangement of the radical cations of butanal and 3‐fluorobutanal: A theoretical investigation of the concerted and stepwise mechanisms

Norberg

Salhi-Benachenhou

2007

J Comput Chem

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“…To compensate this charge, oxygen would exert more electrostatic attraction to remove the electron density from the p electron cloud of the aromatic ring. Such cyclic intermediate states are widely used to explain the mechanism in various reactions [29]. Representative examples can be found in transition metal complex mediated C-H bond activation reactions where the cyclic ring states provide additional energy stabilization to the intermediate species [30][31][32].…”

Section: Resultsmentioning

confidence: 99%

Plasma-enabled sensing of urea and related amides on polyaniline

Puliyalil

Slobodian

Sedlačík

et al. 2016

Front. Chem. Sci. Eng.

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The atmospheric pressure plasma jet (APPJ) was used to enhance the sensitivity of industrially important polyaniline (PANI) for detection of organic vapors from amides. The gas sensing mechanism of PANI is operating on the basis of reversible protonation or deprotonation, whereas the driving force to improve the sensitivity after plasma modifications is unknown. Herein we manage to solve this problem and investigate the sensing mechanism of atmospheric plasma treated PANI for vapor detection of amides using urea as a model. The results from various analytical techniques indicate that the plausible mechanism responsible for the improved sensitivity after plasma treatment is operating through a cyclic transition state formed between the functional groups introduced by plasma treatment and urea. This transition state improved the sensitivity of PANI towards 15 ppm of urea by a factor of 2.4 times compared to the non-treated PANI. This plasma treated PANI is promising for the improvement of the sensitivity and selectivity towards other toxic and carcinogenic amide analytes for gas sensing applications such as improving material processing and controlling food quality.

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“…The dissociation step is suggested (Scheme 8) to occur from ionized enol [14]+', which decomposes competitively by loss of either C(4)H3 or C(6)H3 to give cation a. Rather than a direct 1,3-H migration [ 11]+' + [14]+', the lowest-energy route connecting these two structures is probably formed by the three successive hydrogen transfers [ 11]+' -+ [ 12]+' + [ 13]+' + [ 14]+'. The formal exchange between positions C(4) and C(6) is consequently simply explained by the formation of the radical cation [ 14]+' in the case of the methyl loss.…”

Section: Mechanistic Aspectmentioning

confidence: 99%

“…Rather than a direct 1,3-H migration [ 11]+' + [14]+', the lowest-energy route connecting these two structures is probably formed by the three successive hydrogen transfers [ 11]+' -+ [ 12]+' + [ 13]+' + [ 14]+'. The formal exchange between positions C(4) and C(6) is consequently simply explained by the formation of the radical cation [ 14]+' in the case of the methyl loss. For the other fragmentations, it is necessary to assume that some isomerization steps occur in the backward direction.…”

Section: Mechanistic Aspectmentioning

confidence: 99%

“…First of all, the intermediate structures [9]+'- [ 14]+' and the final state of the fragmentation a + C H ; are indeed below the 653 kJ mol-' limit. The AH;l(a) value has been estimated to be 490 kJ mol-' after measurement of the gas-phase basicity of 3-penten-2-0ne.l~ This leads to a final state ( a ) + CH; situated at 636 kJ mol-' in the 298 K standard enthalpy of formation scale, i.e.…”

Section: Thermochemical Aspectmentioning

confidence: 99%

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Unimolecular dissociations of the [2‐hexanone]⁺˙ metastable ion

Bouchoux

Tortajada

Dagaut

et al. 1987

Org. Mass Spectrom.

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The metastable molecular ion of 2-hexanone loses a methyl radical mainly (-80%) from positions C(4) and C(6), in equal proportions, as indicated by "C labelling. The necessary skeletal rearrangement of the butyl chain is interpreted in terms of a 1,2-[enol-olefin]+' shift. The results and the mechanisms concerning the minor eliminations of CzH4, C,H;, C3H; and C,H, neutrals are also discussed. 4 5 6 k D 3 CD, L J 7 6 Scheme 2. The symbol indicates the position of the 13C label

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Electronic structure of the six-membered cyclic transition state in some .gamma.-hydrogen rearrangements

Cited by 83 publications

References 0 publications

McLafferty rearrangement of the radical cations of butanal and 3‐fluorobutanal: A theoretical investigation of the concerted and stepwise mechanisms

McLafferty rearrangement of the radical cations of butanal and 3‐fluorobutanal: A theoretical investigation of the concerted and stepwise mechanisms

Plasma-enabled sensing of urea and related amides on polyaniline

Unimolecular dissociations of the [2‐hexanone]⁺˙ metastable ion

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Electronic structure of the six-membered cyclic transition state in some .gamma.-hydrogen rearrangements

Cited by 83 publications

References 0 publications

McLafferty rearrangement of the radical cations of butanal and 3‐fluorobutanal: A theoretical investigation of the concerted and stepwise mechanisms

McLafferty rearrangement of the radical cations of butanal and 3‐fluorobutanal: A theoretical investigation of the concerted and stepwise mechanisms

Plasma-enabled sensing of urea and related amides on polyaniline

Unimolecular dissociations of the [2‐hexanone]+˙ metastable ion

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Unimolecular dissociations of the [2‐hexanone]⁺˙ metastable ion