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Radical, allyl

Stabilizing resonances also occur in other systems. Some well-known ones are the allyl radical and square cyclobutadiene. It has been shown that in these cases, the ground-state wave function is constructed from the out-of-phase combination of the two components [24,30]. In Section HI, it is shown that this is also a necessary result of Pauli s principle and the permutational symmetry of the polyelectronic wave function When the number of electron pairs exchanged in a two-state system is even, the ground state is the out-of-phase combination [28]. Three electrons may be considered as two electron pairs, one of which is half-populated. When both electron pahs are fully populated, an antiaromatic system arises ("Section HI). [Pg.330]

We begin by considering a three-atom system, the allyl radical. A two anchor loop applies in this case as illush ated in Figure 12 The phase change takes place at the allyl anchor, and the phase-inverting coordinate is the asymmetric stretch C3 mode of the allyl radical. Quantum chemical calculations confiiin this qualitative view [24,56]. In this particular case only one photochemical product is expected. [Pg.349]

The allyl radical plays an important role in many photochemical transformations, as further discussed in Section IV. [Pg.349]

Just as allyl cation is stabilized by electron delocalization so is allyl radical... [Pg.395]

Allyl radical is a conjugated system in which three electrons are delocalized over three carbons The resonance structures indicate that the unpaired electron has an equal probability of being found at C 1 or C 3 C 2 shares none of the unpaired electron... [Pg.395]

The degree to which allylic radicals are stabilized by delocalization of the unpaired electron causes reactions that generate them to proceed more readily than those that give simple alkyl radicals Compare for example the bond dissociation energies of the pri mary C—H bonds of propane and propene... [Pg.395]

FIGURE 10 3 (a) The spin density (yellow) in allyl radical is equally divided between the two allylic carbons There is a much smaller spin density at C 2 hydrogen (b) The odd electron is in an orbital that is part of the allylic tt system... [Pg.395]

Both resonance forms of the allylic radical must be equivalent... [Pg.397]

Allylic carbocations and allylic radicals are conjugated systems involved as reactive intermediates m chemical reactions The third type of conjugated system that we will examine conjugated dienes, consists of stable molecules... [Pg.398]

Alkenes react with N bromosuccimmide (NBS) to give allylic bromides NBS serves as a source of Br2 and substitution occurs by a free radical mechanism The reaction is used for synthetic purposes only when the two resonance forms of the allylic radical are equivalent Otherwise a mixture of isomeric allylic bromides is produced... [Pg.416]

We attributed the decreased bond dissociation energy in propene to stabilization of allyl radical by electron delocalization Similarly electron delocalization stabilizes benzyl rad ical and weakens the benzylic C—H bond... [Pg.441]

Notice that m converting one resonance form to the next electrons are moved m exactly the same way as was done with allyl radical... [Pg.441]

Resonance theory can also account for the stability of the allyl radical. For example, to form an ethylene radical from ethylene requites a bond dissociation energy of 410 kj/mol (98 kcal/mol), whereas the bond dissociation energy to form an allyl radical from propylene requites 368 kj/mol (88 kcal/mol). This difference results entirely from resonance stabilization. The electron spin resonance spectmm of the allyl radical shows three, not four, types of hydrogen signals. The infrared spectmm shows one type, not two, of carbon—carbon bonds. These data imply the existence, at least on the time scale probed, of a symmetric molecule. The two equivalent resonance stmctures for the allyl radical are as follows ... [Pg.124]

The presence of free radicals can invert this rule, to form anti-Markovnikov products. Free-radical addition in this fashion produces a radical on the central carbon, C-2, which is more stable than the allyl radical. This carbon can then experience further addition. For example, acid-catalyzed addition of... [Pg.124]

Reaction Mechanism. High temperature vapor-phase chlorination of propylene [115-07-17 is a free-radical mechanism in which substitution of an allyhc hydrogen is favored over addition of chlorine to the double bond. Abstraction of allyhc hydrogen is especially favored since the allyl radical intermediate is stabilized by resonance between two symmetrical stmctures, both of which lead to allyl chloride. [Pg.33]

The transition state involves six partially delocalized electrons being transformed from one 1,5-diene system to another. The transition state could range in character from a 1,4-diradical to two nearly independent allyl radicals, depending on whether bond making or bond breaking is more advanced. The general framework for understanding the substituent effects is that the reactions are concerted with a relatively late transition state with well-developed C(l)—C(6) bonds. [Pg.626]

The allyl radical would be expected to be planar in order to maximize n delocalization. Molecular structure parameters have been obtained from EPR, IR, and electron diffraction measurements and confirm that the radical is planar. ... [Pg.679]

The stabilizing effects of vinyl groups (in allylic radicals) and phenyl groups (in benzyl radicals) are very significant and can be satisfactorily rationalized in resonance terminology ... [Pg.692]

A comparison of the rotational barriers in allylic radicals A-D provides evidence for the stabilizing effect of the capto-dative combination ... [Pg.694]

An example of this reaction is the reaction of cyclohexene with t-butyl perbenzoate, which is mediated by Cu(I). " The initial step is the reductive cleavage of the perester. The t-butoxy radical then abstracts hydrogen from cyclohexene to give an allylic radical. The radical is oxidized by Cu(II) to the carbocation, which captures benzoate ion. The net effect is an allylic oxidation. [Pg.724]

Ketones in which the double bond is located in the p,y position are likely candidates for a-cleavage because of the stability of the allyl radical that is formed. This is an important process on direct irradiation. Products then arise by recombination of the radicals or by recombination after decarbonylation. [Pg.763]

The cyclopropane bridge is formed only after hydrogen-atom migration. The driving force for this migration may be the fact that a more stable allylic radical results ... [Pg.777]


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Alkenes allylic radical bromination

Allyl alcohols radical cyclization

Allyl anion radical

Allyl carbonates radical cyclization

Allyl cation, radical, anion

Allyl free radical electronic configuration

Allyl free radical molecular orbitals

Allyl free radical relative stability

Allyl halides radical anions

Allyl radical Allylic bromination

Allyl radical chemistry

Allyl radical cyclization

Allyl radical dissociation

Allyl radical formation

Allyl radical hydrogen bridging

Allyl radical molecular orbital description

Allyl radical molecular orbitals

Allyl radical negative spin density

Allyl radical resonance description

Allyl radical resonance stabilization

Allyl radical resonance structures

Allyl radical spin polarization

Allyl radical substituent effects

Allyl radical valence bond structure

Allyl radical, structure

Allyl radicals bromination

Allyl radicals configurational stability

Allyl radicals configurations

Allyl radicals defined

Allyl radicals dimerization

Allyl radicals electron affinity

Allyl radicals oxidation

Allyl radicals reactions

Allyl radicals rotation

Allyl radicals stability

Allyl radicals trapping

Allyl radicals, rotational barriers

Allyl system radicals

Allyl type free radicals

Allyl-type radicals

Allylation reactions organic radical ions

Allylations free radical

Allylic Free Radicals and Vitamin

Allylic Substitution and the Allyl Radical

Allylic carbon radical halogenation

Allylic free radicals

Allylic halogenation, radical

Allylic radical molecular orbitals

Allylic radical, molecular orbital

Allylic radical, molecular orbital resonance

Allylic radical, molecular orbital spin density surface

Allylic radical, molecular orbital stability

Allylic radical, resonance stability

Allylic radicals

Allylic radicals

Allylic radicals configurations

Allylic radicals defined

Allylic radicals delocalization

Allylic radicals reductive elimination

Allylic radicals resonance delocalization

Allylic radicals structure

Allylic radicals, stability

Allylic species free allyl radicals

Bond strengths in Vinyl, Allyl, and Ethynyl Peroxy Radicals

C-Glycosyl compounds allyl tin radical

Captodative effect allyl radicals

Conjugated organic radicals allyl, propargyl, benzyl and cyclopentadienyl types

Conjugated unsaturated systems allyl radical

Electron delocalization allylic radicals

Electron diffraction, allyl radical

Electronic Configurations of the Allyl Radical, Cation, and Anion

Enantioselective synthesis radical allylation

Excitation allyl radicals

Free Radical Oxidation of an Allylic Position

Free Radical Reactions at Allylic Centers

Free radical allylation

Free radical allylic halogenation

Free radical polymerization allylic

Free radicals allyl

Free radicals allyl, structure

Free radicals allylations, radical reactions

Free-Radical Allylic Bromination

Ground state allyl radicals

Halogenation, radical, allylic benzylic hydrogen

Halogenation, radical, allylic hydrogen

Halogenation, radical, allylic reaction

Hiickel theory allyl radical

Keck radical allylation

Methyl allyl radical

Of allyl radical

Orbital picture of the allyl radical

Peroxide, allyl r-butyl radical addition

Photo-initiated radical allylation

Radical Cyclization of -lodo Allylic Acetals with EtMgBr

Radical Halogenation at an Allylic Carbon

Radical Substitution of Benzylic and Allylic Hydrogens

Radical allyl, orbitals for

Radical allylation

Radical allylation

Radical allylation approach

Radical allylic acetates

Radical allylic bromination

Radical allylic substitution

Radical cations allylic

Radical cations, gaseous allylic cleavage

Radical chain reaction allylic bromination

Radical peroxyl allyl

Radical reactions allylation

Radical reactions allylic bromination

Radical resonance-stabilized allyl

Radicals allylic strain

Radicals) allylations

Radicals) allylations

Radicals, alkoxy allylic

Reductive elimination of allylic radicals

Resolution allyl radical

Resonance allyl radical

Resonance allylic radical

Resonance allylic radical and

Resonance energy allyl radical

Resonance, allyl anion/cation radical

Rotational barriers of allylic radicals

Selective oxidation of propene—the allyl radical

Selective radical bromination allylic substitution of H by Br

Silyl radical allylic-type

Spin density surface, allylic radical

Stability of the Allyl Radical Resonance Revisited

Stability of the allyl radical

Substituents at the Radical Center that Induce Allylic Strain

Substituted Allyl Radicals

Substitution, radical allylic bromination

Sulfides, allyl radical addition reactions

Sulfones, allyl radical cyclizations

The allyl radical

The allylic radical

Twisted allyl radical

Unsaturated system allylic radical

Xanthates radical allylation

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