Triphenylmethyl radical, abstraction

It was nearly ten years before Gomberg s proposal was generally accepted. It now seems clear that what happens is the following the metal abstracts a chlorine atom from triphenylchloromethane to form the free radical triphenyl-methyl two of these radicals then combine to form a dimeric hydrocarbon. But the carbon-carbon bond in the dimer is a very weak one, and even at room temperature can break to regenerate the radicals. Thus an equilibrium exists between the free radicals and the hydrocarbon. Although this equilibrium tends to favor the hydrocarbon, any solution of the dimer contains an appreciable concentration of free triphenylmethyl radicals. The fraction of material existing as free radicals is about 2% in a 1 A/ solution, 10% in a 0.01 M solution, and nearly 100 in very dilute solutions. We could quite correctly label a bottle containing a dilute solution of this substance as triphenylmethyl radicals. ... 

The very first radical to be detected, the triphenylmethyl radical, was made in 1900 by abstraction of Cl" from PhsCCI by Ag metal. 

Some radicals (e.g., triphenylmethyl) are so unreactive that they abstract hydrogens very poorly if at all. Table 14.3 lists some common free radicals in approximate order of reactivity. ... 

Use of triphenylmethyl and cycloheptatrienyl cations as initiators for cationic polymerization provides a convenient method for estimating the absolute reactivity of free ions and ion pairs as propagating intermediates. Mechanisms for the polymerization of vinyl alkyl ethers, N-vinylcarbazole, and tetrahydrofuran, initiated by these reagents, are discussed in detail. Free ions are shown to be much more reactive than ion pairs in most cases, but for hydride abstraction from THF, triphenylmethyl cation is less reactive than its ion pair with hexachlorantimonate ion. Propagation rate coefficients (kP/) for free ion polymerization of isobutyl vinyl ether and N-vinylcarbazole have been determined in CH2Cl2, and for the latter monomer the value of kp is 10s times greater than that for the corresponding free radical polymerization. 

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