Aromatic carbon-halogen bond, cleavage

The influence of electron density distiibution in the radical-anioa on the rate of carbon-halogen bond cleavage was discussed on page 94. This effect makes possible the selective dehalogenation of polyhalogen aromatic compounds. Examples... 

Several research groups ha ve been involved in the study of ET reactions from an electrochemically generated aromatic radical anion to alkyl halides in order to describe the dichotomy between ET and polar substitution (SN2). The mechanism for indirect reduction of alkyl halides by aromatic mediators has been described in several papers. For all aliphatic alkyl halides and most benzylic halides the cleavage of the carbon-halogen bond takes place concertedly with the... 

Of this group only benzyl chloride is not an aryl halide its halogen is not attached to the aromatic ring but to an. v/r -hybridized carbon. Benzyl chloride has the weakest carbon-halogen bond, its measured carbon-chlorine bond dissociation energy being only 293 kJ/mol (70 kcal/mol). Homolytic cleavage of this bond produces a resonance-stabilized benzyl radical. 

Typical examples of the application of DCV for kinetic and mechanistic studies include the cleavage of the carbon-halogen bond in the radical anions of aromatic halides [89], the protonation of radical anions [87,90-92], and the dimerization of radical ions [84]. 

Reduction of aromatic and polyethylenic ketones —pinacols Cleavage of carbon-halogen bonds ... 

Lagrost C, Gmouh S, Vaultier M, Hapiot P (2004) Specific effects of room temperature ionic liquids on cleavage reactivity example of the carbon-halogen bond breaking in aromatic radical anions. J Phys Chem A 108(29) 6175-6182. doi 10.1021/jp049017k... 

Homolytic cleavage of the aryl carbon-halogen bond affords aryl free radicals, which can either arylate a suitable aromatic reaction partner or abstract hydrogen from a hydrogen atom donor (reductive dehalogenation), as first reported over 35 years ago. A recent example is the report by Meunier et al. that photolysis of 1,4-dichlorobenzene in the absence of oxygen yielded 4,4 -dichlorobiphenyl and 2,4, 5-trichlorobiphenyl as reaction products. The general reaction mechanism proceeds as follows ... 

---