Benzhydryl radical

Benzhydryl chloride and bromide are both reduced at a more negative potential than that required for reduction of the benzhydryl radical. Reduction in dimeOiyl-... 

The results reveal the nature of triplet DPC reaction in a quantitative manner. Thus, triplet DPC reacts with cyclohexane and THE at least 100 times as rapidly as does methyl or benzhydryl radical. Triplet DPC is 30 times less reactive with THE than is the phenyl radical. Thus, DPC has a reactivity toward hydrogen abstraction intermediate between those of methyl and phenyl radicals. 

Just as several alkyl substituents increasingly stabilize a radical center (Table 1.2), so do two phenyl substituents. The diphenylmethyl radical ( benzhydryl radical ) is therefore more stable than the benzyl radical. The triphenylmethyl radical ( trityl radical ) is even more stable because of the three phenyl substituents. They actually stabilize the trityl radical to such an extent that it forms by homolysis from the so-called Gomberg hydrocarbon even at room temperature (Figure 1.8). Although this reaction is reversible, the trityl radical is present in equilibrium quantities of about 2 mol%. 

Several new products [e.g. the lactone (307)] were obtained as by-products from remote oxidation of steroids by photochemically excited benzophenone substituents. The benzhydrol asymmetric centre is generated with slight stereoselectivity. Deuterium labelling (at 15a) confirmed that the main product of reaction, the 14-ene (308), results from hydrogen abstraction from C-14 followed by transfer of the 15a-hydrogen to the benzhydryl radical. 

Japanese chemists2 have also reported cases in which the addition of the copper chelate modifies the reactions of carbenes. Thus diphenylcarbene (thermal decomposition of diphenyldiazomethane, 1) is converted mainly into benzophenone azine (2) when generated in an aprotic medium and into 1,1,2,2-tetraphenylethane (3) when generated in a protic medium. The second reaction is considered to proceed by abstraction of hydrogen from the solvent to form benzhydryl radicals which then... 

The first absolute rate constant of a carbene reaction in solution was reported by Closs and Rabinow in 1976. [16] Upon photolysis of diphenyldiazomethane 1 in benzene with a conventional flash lamp, a transient spectrum with X 300 nm was detected. This absorption was assigned to triplet diphenylcarbene 3 because of the correspondence of this spectrum with that previously obtained for this carbene in a low temperature matrix." Upon flash photolysis of diphenyldiazomethane in cyclohexane the transient spectrum of the known spectrum of benzhydryl radical 9 334 nm) was produced. Carbene abstraction... 

Diphenyldiazomethane 1, triplet diphenylcarbene 3 and benzhydryl radical 9 all have significant absorption between 300-340 nm. In practical terms the exci-... 

Despite these complications, graduate student Linda Hadel and Dr. J. C. Scaiano (then of the NRCC in Ottawa) and I were able to obtain useful signals of triplet diphenylcarbene in cyclohexane. [19] The system can be analyzed because triplet DPC is much more reactive towards hydrogen atom donors than is benzhydryl radical thus the time scales of reaction of these two species are very different and can be monitored separately. 

The hydrogen atom abstraction reactions of DPC involve the lower energy, in plane hybrid orbital of the carbene. The carbene consequently has a reactivity closer to phenyl rather than to benzhydryl radical. 

Our work with diphenylcarbene had some technical issues due to overlapping absorptions but was nevertheless straightforward, as the matrix spectrum of the triplet carbene was available and the spectrum of benzhydryl radical was... 

Sailer CF, Thallmair S, Fingeihut BP, Nolte C, Ammer J, Mayr H, Pugliesi 1, de Vivie-Riedle R, Riedle E (2013) A comprehensive microscopic picture of the benzhydryl radical and cation photogeneration and inteiconversion through electron transfer Chem Phys Chem 14 1423... 

The accepted mechanism for the photoreduction of benzophenone in the presence of hydrogen donors includes the steps shown in Eqs. (51)-(54) where B, BH, and RH represent benzophenone, benzhydryl radical, and hydrocarbon, respectively. 

Similarly, in a common application of resonance structures, charge dispersal increases in the order benzyl < j8-naphthylmethyl < -naphthylmethyl and the ionization potentials decrease in the same order. As expected, I for benzhydryl radical is substantially lower than I for benzyl in the cation, positive charge is distributed over two rings instead of one. The effect of the second phenyl group is much less than that of the first perhaps because noncoplanarity of the benzhydryl systems prevents complete conjugation. 

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