Bulletin of the Korean Chemical Society

  • 제13권1호
  • /
  • Pages.32-36
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  • 1992
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  • 0253-2964(pISSN)
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  • 1229-5949(eISSN)
대한화학회 (Korean Chemical Society)
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Theoretical Studies on the Gas-Phase Pyrolysis of 2-Alkoxypyrimidines, 2-Alkoxypyrazines, 4-Ethoxypyrimidine and 3-Ethoxypyridazine

  • 발행 : 1992.02.20
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초록

The gas-phase pyrolysis reactions of 2-alkoxypyrimidines(II), 2-alkoxypyrazines(III), 4-ethoxypyrimidine(IV) and 3-ethoxypyridazine(V) are investigated theoretically using the AM1 MO method. These compounds pyrolyze in a concerted retro-ene process with a six-membered cyclic transition state (TS). The relative order of reactivity if (IV)>(II)>(III)>(V), which can be rationalized by the two effects arising from electron-withdrawing power of the aza-substituent: (ⅰ) Electron withdrawal from the C-O bond accelerates the rate and (ⅱ) electron withdrawal from the $N^1$-atom, that is participating in the six-membered TS, deactivates the reaction. We are unable to explain the experimental result of the greatest reactivity for pyridazine, (V), with our AM1 results. The reactivity increase accompanied by successive methylation of the ethoxy group, ethoxytert-butoxy, is due to a release of steric crowding in the activation process.

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