Significance of Velocity Measurements in Relation to the Benzene Substitution Problem

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FROM the results obtained by Holleman,1 Hückel2 has calculated the relative action constants and the differences between the energies of activation for the nitration of certain benzene derivatives in the ortho, meta, and para positions. The energy of activation for the ortho position is found to be greater than that for the para, and at the temperature used the amount of ortho derivative formed is smaller than that of para in the case of chlor- and brom-benzene, and the exception found in the case of toluene may be met by allowing for the double opportunity of ortho substitution as compared with that of para. These results are interesting from the point of view of steric hindrance. The equality of the action constants taken in conjunction with the facts given above shows that the lower rate of reaction observed for the ortho position is not due to steric hindrance acting on an activated molecule but to an actual paucity of activated molecules due to a difference in activation energy.

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  1. 1

    Rev. Tran. Chim., 18, 267, el seq.; 1899.

  2. 2

    "Theoretische Grundlagen der organischen Chemie" vol. 2, p. 255.

  3. 3

    Rev. Tran. Chim., 35, 1; 1915.

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PEACOCK, D. Significance of Velocity Measurements in Relation to the Benzene Substitution Problem. Nature 129, 57 (1932) doi:10.1038/129057a0

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