Iodine bond strengths

Andrews, M.V., Shaffer, J., McCain, D.C. Nitrogen-iodine bond strength. Thermochemistry of nitrogen triiodide ammine. J. Inorg. Nucl. Chem. 33, 3945-3947 (1971)... 

Several trends are noticeable from the data in the table. The bond strengths of the interhalogens are clearly related to the dift erence in electronegativity between tbe component halogen atoms, as expected on the basis of Pauling s ideas on ionic character (Chapter 5). Furthermore, the tendency to form the higher fluorides and chlorides depends upon the initial eiectronegativiiy of the central atom.- Only iodine forms a heptafluoride or a trichloride. Not shown in Table 17.2 (except indirectly by computation from the values) is the instability of certain lower oxidation states to disproportionation ... 

The role of the halogen atom in the precursors was also explored. Although bromine was mostly used, iodine and chlorine were also employed. While the former gave very efficient cydisation (but with a far more complex mixture of products), the latter gave no reaction at all, reflecting the order of C-X bond strength, Cl>Br>I. 

As shown above, the carbon-iodine bond is stretched, with or without the help of a Lewis acid. The Lewis acid assists in further stretching the carbon-iodine bond. Whether it is needed depends upon the strength of that bond. This strength, in turn, varies with the ability of the solvent, the temperature, and the substituent R to stabilize the center. Depending upon conditions, a Lewis acid can convert... 

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