A theoretical approach to the Birch reduction. Structures and stabilities of cyclohexadienyl radicals

Birch, Arthur J.; Hinde, Alan L.; Radom, Leo

doi:10.1021/ja00532a016

Cited by 34 publications

(5 citation statements)

References 3 publications

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“…28 No attempt has been made to correct the threshold value, which is pertinent to 50 K, to 298 K, but the error involved should be quite small. It is of interest to compare our value with the calculation by Birch et al,29 and this may be done as follows. Tsang 30 shows that the heat of formation at 300 K of cyclohexadienyl radical is 50.0 ± 1.2 kcal mol-I, from which one finds that the energy of hydrogen atom addition to benzene is 21.9 ± 1.2 kcal mol-I.…”

Section: Discussionmentioning

confidence: 99%

Crossed-beam reactive scattering of F2 plus C6H6: Heat of formation of i p s o-fluorocyclohexadienyl radical

Grover¹,

Wen²,

Lee³

et al. 1988

The Journal of Chemical Physics

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Angular distributions and relative total cross sections were measured for products of the collisions of F2 with C6 H6 at relative collision energies of 14 to 26 kcal mol−1 . The most conspicuous product is the ipso-fluorocyclohexadienyl radical i-C6 H6 F ̇, which displays a rather narrow peak very near the center-of-mass angle at all collision energies studied. Product C6 H5 F is masked at M/e=96 by dissociative ionization of C6 H6 F ̇ near the center-of-mass angle, but becomes observable at smaller angles to which little or no C6 H6 F ̇ is scattered. This means that at least one reaction C6 H6 +F2 →C6 H5 F+HF occurs, and does so in such a way that the products acquire high translational energies. The dependence on collision energy of the total cross section for the production of C6 H6 F ̇ was probably measured, and displays a well-marked onset at 13.9±0.3 kcal mol−1. The center-of-mass system means final state translational energy as a function of collision energy was obtained from the angular distributions and goes to zero at 13.9±0.5 kcal mol−1 . This probably means that the onset is a true threshold, from which the heat of formation of the ipso-fluorocyclohexadienyl radical is calculated to be 14.8±0.4 kcal mol−1. The mean final state translational energy asymptotically approaches 3.7 kcal mol−1 as the collision energies are increased, which is so large that only a fraction of the vibrational modes of C6 H6 F ̇ can be involved in the energy partitioning. This conclusion is confirmed by the center-of-mass angular distribution, which favors forward scattering of product F atoms, but only by about 10%–30%. This work shows that the crossed-beam method can be used to make precision thermochemical measurements of gaseous polyatomic free radicals. It also reports the investigation of a polyatomic–polyatomic reaction in crossed beams, for which type of study there are still very few examples.

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Section: Discussionmentioning

confidence: 99%

Crossed-beam reactive scattering of F2 plus C6H6: Heat of formation of i p s o-fluorocyclohexadienyl radical

Grover¹,

Wen²,

Lee³

et al. 1988

The Journal of Chemical Physics

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“…In agreement with experiment, radical attack ortho to the methoxy group was calculated to be favored over para attack. The greater stabilization of the cyclohexadienyl radical by the methoxy group at the 1-position rather than the 3-position provides the basic origin of the selectivity (Figure ) …”

Section: Enamine/iminium Catalysismentioning

confidence: 99%

Quantum Mechanical Investigations of Organocatalysis: Mechanisms, Reactivities, and Selectivities

et al. 2011

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“…One of our groups has shown that the reactions proceed via a three-π-electron radical cation species generated by one-electron oxidation of a chiral enamine. In reports on intramolecular α-arylation reactions from the Nicolaou group and one of our laboratories, the cyclization of enamine radical cation 4 was shown to selectively attack ortho to the methoxy group (Scheme ). , It was proposed that an intermediate best represented as 5 (rather than 6 described earlier) was involved. The Nicolaou group showed that 1,3,4-trisubstituted aldehydes 8 − 10 , however, react to give para aryl products 11 − 13 (Scheme ).…”

Section: Introductionmentioning

confidence: 99%

Nature of Intermediates in Organo-SOMO Catalysis of α-Arylation of Aldehydes

et al. 2010

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The intramolecular α-arylation of aldehydes via organo-SOMO catalysis was investigated using density functional theory (B3LYP and M06-2X functionals). The geometries, spin densities, Mulliken charges, and molecular orbitals of the reacting enamine radical cations were analyzed, and the nature of the resulting cyclized radical cation intermediates were characterized. In agreement with experimental observations, the calculated 1,3-disubstituted aromatic system shows ortho selectivity, while the 1,3,4-trisubstituted systems show para, meta (instead of ortho, meta) selectivity. The selectivity change for the trisubstituted rings is attributed to a distortion of the ortho substituents in the ortho, meta cyclization transition structures, causing a destabilization of these isomers and therefore selectivity for the para, meta product.

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A theoretical approach to the Birch reduction. Structures and stabilities of cyclohexadienyl radicals

Cited by 34 publications

References 3 publications

Crossed-beam reactive scattering of F2 plus C6H6: Heat of formation of i p s o-fluorocyclohexadienyl radical

Crossed-beam reactive scattering of F2 plus C6H6: Heat of formation of i p s o-fluorocyclohexadienyl radical

Quantum Mechanical Investigations of Organocatalysis: Mechanisms, Reactivities, and Selectivities

Nature of Intermediates in Organo-SOMO Catalysis of α-Arylation of Aldehydes

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