Radical Addition Reactions

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VARIOUS theories have been advanced to explain the direction of addition of neutral unsymmetrical radical reagents to unsymmetrical unsaturated systems. Such addition is often ‘abnormal' as compared with the ‘normal' additions observed with ionic reagents. Thus Waters1 states that "free radicals . . . react preferentially at points of high electron density", and Mayo and Walling2 have suggested that the direction of addition is governed by the relative heats of formation of the two alternative intermediates in the addition. No disagreement with the views of the latter authors can be advanced because there is, in general, no method of accurately evaluating such constants. The statement by Waters, on the other hand, is not in agreement with the present experimental data, since his view would imply that neutral radicals are electrophilic in character.

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  1. 1

    Waters, W. A., "The Chemistry of Free Radicals", 183 (Oxford University Press, 1946); compare Kharasch, M. S., Engelman, H., and Mayo, F. R., J. Org. Chem., 2, 288 (1937).

  2. 2

    Mayo, F. R., and Walling, C., Chem. Rev., 27, 351 (1940).

  3. 3

    Price, C. C., "Mechanisms of Reactions at Carbon-Carbon Double Bonds", 63 (Interscience Publishers, Inc., 1946); see also Remick, A. E., "Electronic Interpretations of Organic Chemistry", 275 (J. Wiley and Sons, 1943).

  4. 4

    Koelsch, C. F., and Boekelheide, V., J. Amer. Chem. Soc., 66, 412 (1944).

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BARTON, D. Radical Addition Reactions. Nature 162, 182–183 (1948) doi:10.1038/162182a0

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