STRUCTURE OF CARBENE, CH<sub>2</sub>

Skell, P. S.; Woodworth, Robert C.

doi:10.1021/ja01598a087

Cited by 220 publications

(90 citation statements)

References 2 publications

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“…In the addition of singlet methylene t o 2-butene, the olefin 2-methyl-1-butene is seen only at low pressures where the isomerization of the initially formed cyclopropanes is not completely quenched. However, the trimethylene intermediate produced (7) and is in accord with the predictions of Hoffmann (3), the experimental observations of Crawford and Ali (6), and the idea of Skell and Woodworth put forward in 1956 (16).…”

Section: " ' Not Observedsupporting

confidence: 77%

Photolysis of some alkyl-1-pyrazolines

Moore¹,

Mishra²,

Crawford³

1968

Can. J. Chem.

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The direct and photosensitized photolysis of six methylated-1-pyrazolines is described. Examination of the products suggests that direct photolysis leads to ari excited singlet trimethylene, whereas a triplet is produced on benzophenone photosensitization. The trimethylene produced from 4 and 5 is related to the intermediates produced on addition of triplet methylenes to cis-and trans-2-butene. Evidence is presented to support the claim that no intermediate is involved in the addition of singlet methylene to cisand tratu-2-butene.

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Section: " ' Not Observedsupporting

confidence: 77%

Photolysis of some alkyl-1-pyrazolines

Moore¹,

Mishra²,

Crawford³

1968

Can. J. Chem.

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“…Studies on the P450cam-catalyzed epoxidation of trans-1-phenyl-2-vinylcyclopropane, a very sensitive radical clock probe, provided no evidence for the involvement of radicals or cations in the reaction (46). Collectively, the stereochemical and radical clock results may be interpreted to reflect an oxygen insertion by an oxenoid-heme species (reaction B), reminiscent of the insertion of carbenes into olefinic bonds (47,48). Alternatively, the radical clock studies, in conjunction with the stereochemical and mutagenesis findings presented in the present paper, could be explained by a mechanism (reaction C) in which the hydroperoxo-heme complex is the oxidant, resulting in epoxidation of the olefin by a concerted mechanism, similar to peracid epoxidation of olefins.…”

Section: Resultsmentioning

confidence: 99%

Epoxidation of olefins by cytochrome P450: Evidence from site-specific mutagenesis for hydroperoxo-iron as an electrophilic oxidant

Vaz

McGinnity

Coon

1998

Proc. Natl. Acad. Sci. U.S.A.

305

245

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P450 cytochromes (P450) catalyze many types of oxidative reactions, including the conversion of olefinic substrates to epoxides by oxygen insertion. In some instances epoxidation leads to the formation of products of physiological importance from naturally occurring substrates, such as arachidonic acid, and to the toxicity, carcinogenicity, or teratogenicity of foreign compounds, including drugs. In the present mechanistic study, the rates of oxidation of model olefins were determined with N-terminal-truncated P450s 2B4 and 2E1 and their respective mutants in which the threonine believed to facilitate proton delivery to the active site was replaced by alanine. Styrene epoxidation, cyclohexene epoxidation and hydroxylation to give 1-cyclohexene-3-ol, and cis-or trans-butene epoxidation (without isomerization) and hydroxylation to give 2-butene-1-ol were all significantly decreased by the 2B4 T302A mutation. Reduced proton delivery in this mutant is believed to interfere with the activation of dioxygen to the oxenoid species, as shown earlier by decreased hydroxylation of several substrates and enhanced aldehyde deformylation via a presumed peroxo intermediate. Of particular interest, however, the T303A mutation of P450 2E1 resulted in enhanced epoxidation of all of the model olefins along with decreased allylic hydroxylation of cyclohexene and butene. These results and a comparison of the ratios of the rates of epoxidation and hydroxylation support the concept that two different species with electrophilic properties, hydroperoxo-iron (FeO 2 H) 3؉ and oxenoid-iron (FeO) 3؉ , can effect olefin epoxidation. The ability of cytochrome P450 to use several different active oxidants generated from molecular oxygen may help account for the broad reaction specificity and variety of products formed by this versatile catalyst.

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“…The addition of singlet carbenes to alkenes is well known to proceed in a single step [31][32][33] and in a non-least-motion fashion, [4,[34][35][36] as the least-motion mechanism is symmetry-forbidden in the sense of the WoodwardHoffmann rules. [37] The reaction is generally considered to proceed in two phases: in the first the carbene approaches suprafacially to the p system and thereby maximizes the electrophilic carbene-alkene interaction, that is, the HOMOA C H T U N G T R E N N U N G (olefin)-LUMOA C H T U N G T R E N N U N G (carbene) interaction in terms of frontier orbital theory.…”

Section: Resultsmentioning

confidence: 99%

Addition of Carbenes to the Sidewalls of Single‐Walled Carbon Nanotubes

Bettinger

2006

Chemistry A European J

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The addition of carbenes CX(2) (X=H, Cl) to single-walled carbon nanotubes (SWNTs) was investigated by density functional theory and finite, hydrogen-terminated nanotube clusters or periodic boundary conditions in conjunction with basis sets of up to polarized triple-zeta quality. For armchair [(3,3) to (12,12)] and zigzag tubes [(3,0) to (18,0)], reaction of CH(2) with the C--C bond oriented along the tube axis (A) is less exothermic than with those C--C bonds having circumferential (C) orientation. This preference decreases monotonically with increasing tube diameter for armchair, but not for zigzag tubes; here, tubes with small band gaps have a very low preference for circumferential addition. Axial addition results in cyclopropane products, while circumferential addition produces "open" structures for both armchair and zigzag tubes. The barriers for addition of dichlorocarbene to a (5,5) SWNT, studied for a finite C(90)H(20) cluster, are higher than that for addition to C(60), in spite of similar diameters of the carbon materials. Whereas addition of CCl(2) to [60]fullerene proceeds in a concerted fashion, addition to a (5,5) armchair SWNT is predicted to occur stepwise and involve a diradicaloid intermediate according to B3LYP, PBE, and GVB-PP computations. Addition to C bonds of (5,5) armchair tubes resulting in the thermodynamically more stable insertion products is kinetically less favorable than that to A bonds yielding cyclopropane derivatives.

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STRUCTURE OF CARBENE, CH₂

Cited by 220 publications

References 2 publications

Photolysis of some alkyl-1-pyrazolines

Photolysis of some alkyl-1-pyrazolines

Epoxidation of olefins by cytochrome P450: Evidence from site-specific mutagenesis for hydroperoxo-iron as an electrophilic oxidant

Addition of Carbenes to the Sidewalls of Single‐Walled Carbon Nanotubes

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STRUCTURE OF CARBENE, CH2

Cited by 220 publications

References 2 publications

Photolysis of some alkyl-1-pyrazolines

Photolysis of some alkyl-1-pyrazolines

Epoxidation of olefins by cytochrome P450: Evidence from site-specific mutagenesis for hydroperoxo-iron as an electrophilic oxidant

Addition of Carbenes to the Sidewalls of Single‐Walled Carbon Nanotubes

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STRUCTURE OF CARBENE, CH₂