Kinetic studies of substituent effects in electrophilic aromatic hydrogen exchange

4 Kinetic studies of substituent effects in electrophilic aromatic hydrogen exchange 

The advantages of the hydrogen exchange as a model electrophilic aromatic substitution are now well recognised and have been emphasised504, 522, 523, so that a very considerable body of data is now to be found in the literature. In order to simplify presentation of this, the data are considered under headings of the acid medium employed for the studies. 

RATE COEFFICIENTS AND ACTIVATION ENERGIES FOR REACTION OF [3H]-Ar (OR[2H]-Ar WHERE INDICATED) WITH ANHYDROUS CF3COOH 

0 These results obtained with a medium containing 2 % of carbon tetrachloride. 

8 times slower than for dedeuteration (Table 159) as expected532. The values of the rate coefficients decreased with time during a run due to slower deuteration at the a positions, the corresponding rates after an approximately equal interval of time being ca. 160, 70, and 170. It appears then that the a position of 1,3-dioxole is significantly less reactive than the a position of the other two molecules 

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