1,3-hydrogen shift in propene radical cation: a facile antarafacial rearrangement

Nguyen, Minh Tho; Landuyt, Luc; Vanquickenborne, L. G.

doi:10.1016/0009-2614(91)80205-c

Cited by 16 publications

(10 citation statements)

References 18 publications

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“…Whether conservation of orbital symmetry is important in the chemistry of open shell species is sometimes questioned. A number of 1,3-H-shifts in radical cations have now been characterized by theory, and all of those circumvent pathways that violate conservation of orbital symmetry [19,20,22]. Some of those expend substantial energy to take symmetry-allowed pathways through antarafacial transition states [19], some have transition states at the boundary between being antarafacial and suprafacial (present results), and some utilize subjacent orbitals to take suprafacial pathways (present results).…”

Section: 1mentioning

confidence: 55%

“…Nonetheless 1,3-H-shifts do occur [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], or would were it not for competition from lower energy processes [18 -23]. Theoretical studies conducted since the work of Woodward and Hoffmann show that 1,3-H-shifts across -bonds can be antarafacial [19,20,22], suprafacial [22], or at the boundary between the two such that they are neither antarafacial nor suprafacial [22], a surprising diversity of trajectories.…”

mentioning

confidence: 99%

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Circumvention of orbital symmetry restraints by 1,3-H-shifts of enolic radical cations

McAdoo

2004

J. Am. Soc. Mass Spectrom.

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The reaction coordinates of 1,3-H-shifts across double bonds are traced by theory for three reactions, CH 3 C(OH)CH 2 ϩ⅐ (1) 3 CH 3 C(O ϩ⅐ )CH 3 (2), CH 2 C(OH) 2 ϩ⅐ (3) 3 CH 3 CO 2 H ϩ⅐ (4) and CH 3 C(OH)CH 2 ϩ⅐ (1) 3 CH 2 C(OH)CH 3 ϩ⅐ (1Ј), to explore how the need to conserve orbital symmetry influences the pathways for these reactions. In the first and second reactions, prior to the start of the H-transfer the methylene rotates from being in the skeletal plane to being bisected by it. Thus these reactions are neither antarafacial nor suprafacial, but precisely between those possibilities. This stems from a counterbalancing between the need to conserve orbital symmetry and the large distorting forces required to attain an allowed antarafacial transition state. In contrast to the first two reactions, 1 3 1Ј follows a suprafacial pathway. However, this pathway does not violate conservation of orbital symmetry, as it utilizes lower lying orbitals of appropriate symmetry rather than the antisymmetric uppermost occupied allyl-type orbital. Changes in geometry which presumably produce asymmetric vibrational excitation and the unequal losses of methyl that follow 1 3 2, i.e., nonergodic behavior, are also characterized. (J Am Soc Mass Spectrom 2004, 15, 972-981)

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Section: 1mentioning

confidence: 55%

mentioning

confidence: 99%

Circumvention of orbital symmetry restraints by 1,3-H-shifts of enolic radical cations

McAdoo

2004

J. Am. Soc. Mass Spectrom.

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“…At the MP2 level the process is described as two consecutive [1,2]-shifts, since the C s structure is a shallow minimum instead of a transition structure; but this may be an artifact of the method . Nguyen et al reported that for the radical cation the rearrangement occurs via an antarafacial pathway with a C s transition structure involving a hydride transfer . In contrast, the process in neutral propene has a C 2 transition structure and a migrating proton.…”

Section: Resultsmentioning

confidence: 99%

Pathways for the Reaction of the Butadiene Radical Cation, [C₄H₆]^•+, with Ethylene

Hofmann

Schaefer

1999

J. Phys. Chem. A

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Reaction pathways for the addition of ethylene, 1, to butadiene radical cation, 2, involving H-shifts have been investigated at the coupled cluster UCCSD(T)/DZP//UMP2(fc)/DZP + ZPE level of theory. Activation energies are relatively low for [1,2]- (10.0 kcal mol-1, TS-4/20) and [1,5]-hydrogen shifts (7.7 kcal mol-1, TS-4/26) but are relatively high for [1,4]- (33.8 kcal mol-1, TS-4/14) and [1,3]-H shifts (e.g. 42.2 kcal mol-1, TS-12/13; 57.2 kcal mol-1, TS-16/21). Several rearrangement reactions have been found to occur below the energy limit of separated 1 + 2. The cyclopentenyl cation, [C5H7]+, 18, experimentally observed as reaction product of the butadiene radical cation, 2, and ethylene, 1, in the gas phase may origin from various reaction pathways. The following reaction sequence has been identified as the lowest in energy path from 1 + 2 to 18 with all relative energies (ΔE°) of transition structures below that of 1 + 2: (a) ethylene adds to the butadiene radical cation to form an open-chain distonic intermediate, 4, that undergoes a [1,5]-H shift to the 1,4-hexadiene radical cation, 26; (b) intramolecular [2+1] cycloaddition to methyl-cyclopenta-1,3-diyl intermediates, 22 and 24, which can interconvert through a bicyclo[2.1.0]pentane radical cation, 23; (c) [1,2]-H shift of 24 to the 3-methyl cyclopentene radical cation, 16; (d) methyl radical loss to give cyclopenten-3-yl cation, 18. Along this reaction pathway, ΔH 298 changes by −18.1 kcal mol-1 (ΔG 298 by −16.0 kcal mol-1) and only transition structures low in energy (ΔH 298 is below that of 1 + 2; max. ΔG 298⧧ = 10.4 kcal mol-1 for [1,5]-H shift relative to 1 + 2) are involved. Ethylene, 1, can also add to 2, simultaneously accepting a transferred hydrogen to give a 1,3-hexadiene radical cation. Back dissociation of the latter into 1 + 2 is favored over methyl radical loss.

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“…In particular, isomerization between both distonic species 2b and 2c is prohibited by a substantial energy barrier, namely 180 kJ/mol relative to 2b . It has been established that the 1,3-H shift is a difficult process in the neutral state but becomes strongly accelerated upon ionization . In addition, the low-energy position of TS 2a / 2b , which lies well below both dissociation limits CH 3 CHSH + + H • ( 2d ) and H 2 CCH 2 + SH 2 •+ ( 2f ), suggests that the ion system is likely to undergo a preliminary isomerization 2a → 2b before dissociating into fragments.…”

Section: Resultsmentioning

confidence: 99%

Novel β-Distonic Radical Cations [C_nH₂_n₊₂S]^•+ (n = 2, 3) Formed upon Decarbonylation of Ionized S-Alkyl Thioformates: A Mass Spectrometric and ab Initio Study

1997

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Decarbonylation is commonly observed in the 70 eV electron impact mass spectra of a series of S-alkyl thioformates, H−C(O)SR 1−7. Using a combination of collisional activation (CA) and neutralization−reionization (NR) mass spectra, it is shown that the spectra of the so-formed [M−CO]•+ ions differ from the isomeric alkane thiol ions (RSH•+), if R > CH3. These fragment ions are therefore distonic radical cations, and given the fact that the α-distonic •CH2−S+H2 ions are not present under our experimental conditions, it is proposed that they actually are β-distonic ions. Strong evidence for the distonic nature of the fragment ions derived from 2−7 •+ has been obtained owing to the use of a new hybrid tandem mass spectrometer presenting a sector−quadrupole−sector configuration. In the case of ethyl derivatives (R = C2H5), both the distonic •CH2CH2S+H2 (2b) and conventional CH3CH2SH•+ (2a) ions are observed. The nonclassical structure 2b reacts indeed with nitric oxide (NO•) giving the production of H2S+−NO ions (m/z 64), characterized by high-energy collisional activation. Distonic ions 2b have also been otherwise prepared in an ion−molecule reaction involving the transfer of ionized ethene from •CH2CH2O+CH2 to neutral hydrogen sulfide, H2S. Upon CA, the resulting ions 2b show the same behavior as the product of decarbonylation of the S-ethyl thioformate molecular ions. Upon neutralization−reionization, the distonic isomers of the alkane thiol ions give rise to intense peaks corresponding to H2S•+ and ionized olefins. Portions of the potential energy surface related to the rearrangement and dissociation processes in the [C2H6S]•+ system have also been constructed using ab initio molecular orbital calculations at the QCISD(T)/6-311++G(d,p)//UMP2/6-31G(d,p) level. Theoretical results provide further support for the observation of β-distonic ions.

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1,3-hydrogen shift in propene radical cation: a facile antarafacial rearrangement

Cited by 16 publications

References 18 publications

Circumvention of orbital symmetry restraints by 1,3-H-shifts of enolic radical cations

Circumvention of orbital symmetry restraints by 1,3-H-shifts of enolic radical cations

Pathways for the Reaction of the Butadiene Radical Cation, [C₄H₆]^•+, with Ethylene

Novel β-Distonic Radical Cations [C_nH₂_n₊₂S]^•+ (n = 2, 3) Formed upon Decarbonylation of Ionized S-Alkyl Thioformates: A Mass Spectrometric and ab Initio Study

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1,3-hydrogen shift in propene radical cation: a facile antarafacial rearrangement

Cited by 16 publications

References 18 publications

Circumvention of orbital symmetry restraints by 1,3-H-shifts of enolic radical cations

Circumvention of orbital symmetry restraints by 1,3-H-shifts of enolic radical cations

Pathways for the Reaction of the Butadiene Radical Cation, [C4H6]•+, with Ethylene

Novel β-Distonic Radical Cations [CnH2n+2S]•+ (n = 2, 3) Formed upon Decarbonylation of Ionized S-Alkyl Thioformates: A Mass Spectrometric and ab Initio Study

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Pathways for the Reaction of the Butadiene Radical Cation, [C₄H₆]^•+, with Ethylene

Novel β-Distonic Radical Cations [C_nH₂_n₊₂S]^•+ (n = 2, 3) Formed upon Decarbonylation of Ionized S-Alkyl Thioformates: A Mass Spectrometric and ab Initio Study