Benzene-iodine complex, charge-transfer reaction

Microscopic Solvation and Femtochemistry of Charge-Transfer Reactions The Problem of Benzene(s)-Iodine Binary Complexes and Their Solvent Structures, P. Y. Cheng, D. Zhong, and A. H. Zewail, Chem. Phys. Leu. 242, 368 (1995). 

Processes involving a single-electron transfer (SET) step and cation-radical intermediates can occur in the reactions of X - or X -iodanes with electron-rich organic substrates in polar, non-nucleophilic solvents. Kita and coworkers first found that the reactions of p-substituted phenol ethers 29 with [bis(trifluoroacetoxy)iodo]benzene in the presence of some nucleophiles in fluoroalcohol solvents afford products of nucleophilic aromatic substitution 31 via a SET mechanism (Scheme 1.5) [212,213]. On the basis of detailed UV and ESR spectroscopic measurements, it was confirmed that this process involves the generation of cation-radicals 30 produced by SET oxidation through the charge-transfer complex of phenyl ethers with the hypervalent iodine reagent [213,214],... 

The effect of the former can be seen well, for instance, from a comparison of the reactions between iodine and tetraalkyl lead in benzene and in carbon tetrachloride [Pi 68]. In spite of the facts that both solvents are apolar and have small relative permittivities, and neither of them solvates the tetraalkyl lead molecule, the reaction takes place at a rate 15-20 times higher in benzene than in carbon tetrachloride solution. The explanation of the phenomenon is that with benzene iodine forms a charge-transfer complex of relatively high stability this causes a greater polarization of the iodine molecule than does the very weak interaction between iodine and carbon tetrachloride. 

Charge-transfer complex reactions. Iodine + benzene... 

Figure 2 Far-IR spectra of an 0.2 M iodine solution in benzene. The upper diagram shows the absorption coefficient and the lower diagram the infrared spectral density Uriy) as calculated according to Eq. (6) see text. [From M Besnard. Chemical kinetics and vibrational spectroscopy An analysis of weak charge transfer complexing reactions. In Molecular Liquids New Perspectives in Physics and Chemistry, JJC Teixeira-Dias, ed. Dordrecht Kluwer Academic, 1992, p 469. Reproduced with kind permission from Kluwer Academic Publishers.]...

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