物理化学学报 >> 1994, Vol. 10 >> Issue (11): 1004-1008.doi: 10.3866/PKU.WHXB19941108

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HNCO热解为CO2和HNCNH的反应机理理论研究

张绍文, 傅孝愿   

  1. 北京师范大学化学系,北京 100875
  • 收稿日期:1993-10-13 修回日期:1993-11-27 发布日期:1994-11-15
  • 通讯作者: 傅孝愿

A Theoretical Study on the Thermo Decomposition of HNCO to HNCNH and CO2

Zhang Shao-Wen, Fu Xiao-Yuan   

  1. Department of Chemistry,Beijing Normal University,Beijing 100875
  • Received:1993-10-13 Revised:1993-11-27 Published:1994-11-15
  • Contact: Fu Xiao-Yuan

摘要:

利用从头算RHF/3-21G方法研究了HNCO二聚后生成HNCNH和CO2的反应机理,计算表明,该反应是分步反应,由反应物经第一过渡态生成四元环中间体,再经过第二过渡态分解为产物,与实验得到的结论一致,反应的第一步是速度控制步骤,计算得到的活化位垒为172.55kJ•mol-1,与实验上测得的176.40±16.30kJ•mol-1相吻合,反应的第二位垒为83.68kJ•mol-1,在实验条件下是一个快速步骤.因此,四元环中间体不能作为最终产物.整个反应是包含两个非同步过程的加成反应.

关键词: HNCO, 热解机理, 从头算方法

Abstract:

 Ab initio RHF/3-21G method has been employed to study the mechanism of the bimolecular thermolysis of HNCO. The results show that this reaction is a stepwise reaction. The first step is the dimerization of HNCO to form a four-membered ring intermediate, the second step is the dissociation of the intermediate to form the products HNCNH and CO2. The calculated activation barrier for the steps are 172.55kJ•mol-1 and 83.68kJ•mol-1, respectively. It can be seen that the first step is the rate determining step, its barrier is in good agreement with experimental data (activation energy: 176.40±16.30 kJ•mol-1). The second step is a fast step, the four-membered ring intermediate can not stay as a final product. The reaction can be described as a stepwise non-synchronous reaction.

Key words: HNCO, Thermolysis mechanism, Ab initio method