物理化学学报 >> 1996, Vol. 12 >> Issue (06): 496-501.doi: 10.3866/PKU.WHXB19960604

研究论文 上一篇    下一篇

亚甲基烯酮与5-亚甲基-1,3-二噁烷-4,6-二酮反应机理的研究

盛颖宏,方德彩,傅孝愿   

  1. 北京师范大学化学系,北京 100875
  • 收稿日期:1995-10-04 修回日期:1996-01-29 发布日期:1996-06-15
  • 通讯作者: 傅孝愿

Theoretical Study on the Mechanism of the Cycloaddition Reactions Between Methyleneketene and 5-methylene-1,3-dioxan-4,6-dione

Sheng Ying-Hong,Fang De-Cai,Fu Xiao-Yuan   

  1. Department of Chemistry,Beijing Normal University,Beijing 100875
  • Received:1995-10-04 Revised:1996-01-29 Published:1996-06-15
  • Contact: Fu Xiao-Yuan

摘要:

利用半经验分子轨道理论AM1方法,研究了5-亚甲基-1,3-二噁烷-4,6-二酮与亚甲基烯酮的2,3-位C=C,3,4-位C=O和1,2-位C=O三种双键位置上的环加成反应的反应机理.采用Berny梯度法优化得到反应的过渡态,并进行了振动分析确认.计算结果表明,环加成反应是按照协同的非同步途径进行的,经过一个扭曲的六员环过渡态,前线轨道分析表明反应机理为[4+2]机理.根据AM1优化得到的产物反应物及过渡态的生成热可知三个反应的活化焓分别为27.07kJ•mol-1,32.41kJ•mol-1和137.96kJ•mol-1,2,3-位C=C双键上的环加成反应的活化焓最低,这与实验中只观察到2,3-位C=C双键上环加成产物的结论是一致的.

关键词: 亚甲基烯酮, 5-亚甲基-1, 3-二噁烷-4, 6-二酮, 环加成反应, 区域选择性, 反应机理

Abstract:

Three different reaction schemes for the cycloaddition reactions between methyleneketene and 5-methylene-1,3-dioxan-4,6-dione have been studied by means of semiempirical AM1 method. All the geometries of the stationary points on the reactions path have been optimized by energy gradient technique, and all transition states were characterized by vibration frequency analysis. The results can be summed up as follows: the cycloaddition of different double bond of methyleneketene with 5-methylene- 1,3-dioxan-4,6-dione are all concerted but nonsynchrorous, taking place through twisted transition states. An analysis based on frontier molecular orbital theory shows that the reaction mechanisms correspond to [4+2] description. The activation barriers were calculated to be 24.07k J •mol- 1, 32.41 k J•mol-1 and 137.96 kJ•mol- 1 respectively. The regio-selectivity of the reactions observed by experiments was correctly predicted by the calculations.

Key words: Methyleneketene, 5-methylene-1,3-dioxan-4,6-dione, Cycloaddition, Region-selectivity, Reaction mechanism