91Ó°ÊÓ

The magnitudes and signs of the \(\sigma\) constants associated with meta and para substituents can be rationalized in terms of inductive and electron- delocalization influences. Show how it is possible, within this framework, to account for the following facts: a. Fluorine has a sizable positive \(\sigma\) constant when meta but almost zero when para. b. The \(\sigma\) constant of the methoxy group \(\left(-\mathrm{OCH}_{3}\right)\) is positive in the meta position an negative in the para position. c. The \(-\stackrel{\oplus}{\mathrm{N}}\left(\mathrm{CH}_{3}\right)_{3}\) group has a slightly larger positive \(\sigma\) constant in the meta position than in the para position, but the reverse is true for the \(-\mathrm{N}_{2}^{+}\) group. d.* The \(\sigma\) constant of the \(-\mathrm{CF}_{3}\) group is more positive when para than when meta.

For each of the following pairs of compounds give a chemical test, preferably a test-tube reaction, that will distinguish between the two compounds. Write a structural formula for each compound and equations for the reactions involved. a. benzenol and cyclohexanol b. methyl 4-hydroxybenzoate and 4-methoxybenzoic acid c. 1,4 - and 1,3-benzenediol d. 1,4 -benzenediol and tropolone e. 9,10 -anthracenedione and 1,4 -anthracenedione

When 2-hydroxybenzoic acid (salicylic acid) is treated with excess bromine in aqueous solution, it forms 2,4,6-tribromobenzenol. Write a reasonable mechanism for this reaction. Would you expect the same type of reaction to occur with 3-hydroxybenzoic acid?