The gas-phase pyrolysis reactions of iminoethers (ケ), 2-alkoxypyridines (ゲ), 2-N-alkylated pyridones (コ) and N-alkylated acetamides (ゴ) have been studied MO theoretically with the AM1 method. The decomposition of these compounds proceeds by a concerted retro-ene process through a six-membered cyclic transition state. The reactivity decreases in the order (ケ) > (ゲ) > (コ) > (ゴ), with a greater reactivity for the imine series, (ケ) and (ゲ), compared to the amide series, (コ) and (ゴ), and a difference in basicity between the N and O atoms. Within a given series, however, the reactivity is dictated mainly by the aromaticity in the transition state. The reactivity order with respect to side alkyl chain of a species was found to increase as the steric crowding effect increases. The AM1 reactivity in this work agree well with the experimental results.
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