Ab Initio and RRKM Study of the Unimolecular Decomposition of Five-membered Ring Heterocyclic (X:O,S,N-H)  

作　　者：Abolfazl Shiroudi Ehsan Zahedi 

机构地区：[1]Chemistry Department,Shahrood Branch,Islamic Azad University

出　　处：《Chinese Journal of Structural Chemistry》2012年第8期1121-1128,共8页结构化学（英文）

摘　　要：Quantum mechanical and Rice-Ramsperger-Kassel-Marcus （RRKM） calculations are carried out to study the thermal unimolecular decomposition of 2,5-dihydrofuran （1）,2,5dihydrothiophene （2）,and 3-pyrroline （3） at the MPW1PW91/6-31＋＋G level of theory,and the results are in good agreement with the experimental values.The predicted high pressure limit rate constants （k（T）） in various states of activation energy and pre-exponential （S1：（A（calc.）,E a（calc.））,S2：（A （calc.）,E a（exp.））,and S3：（A （exp.）,E a（calc.））） for the thermal decomposition processes 1-3 were evaluated.Also,the fall-off pressures （P1/2） for compounds 1-3 in the states 1-3 are found to be （1.24×10-2,1.09×10-3,and 4.19×10-2mmHg）,（1.24×10-2,1.63×10-3,and 2.79×10-2mmHg）,and （1.24×10-2,1.63×10-3,and 4.19×10-2 mmHg）,respectively.As the fall-off pressure of thermal decomposition process of compounds 1-3 is in the following order：P1/2（3）〉 P1/2（1）〉 P1/2 （2）,the decomposition rates are as below：rate（3） 〈rate（1）〈rate（2）.Quantum mechanical and Rice-Ramsperger-Kassel-Marcus （RRKM） calculations are carried out to study the thermal unimolecular decomposition of 2,5-dihydrofuran （1）,2,5dihydrothiophene （2）,and 3-pyrroline （3） at the MPW1PW91/6-31＋＋G level of theory,and the results are in good agreement with the experimental values.The predicted high pressure limit rate constants （k（T）） in various states of activation energy and pre-exponential （S1：（A（calc.）,E a（calc.））,S2：（A （calc.）,E a（exp.））,and S3：（A （exp.）,E a（calc.））） for the thermal decomposition processes 1-3 were evaluated.Also,the fall-off pressures （P1/2） for compounds 1-3 in the states 1-3 are found to be （1.24×10-2,1.09×10-3,and 4.19×10-2mmHg）,（1.24×10-2,1.63×10-3,and 2.79×10-2mmHg）,and （1.24×10-2,1.63×10-3,and 4.19×10-2 mmHg）,respectively.As the fall-off pressure of thermal decomposition process of compounds 1-3 is in the following order：P1/2（3）〉 P1/2（1）〉 P1/2 （2）,the decomposition rates are as below：rate（3） 〈rate（1）〈rate（2）.

关 键 词：unimolecular calculate method molecular modeling decomposition fall-off pressure RRKM 

分 类 号：O626[理学—有机化学]