### 硝基烃光异构化反应的密度泛函理论计算

1. (浙江理工大学理学院应用化学系, 教育部先进纺织材料重点实验室, 杭州 310018)
• 收稿日期:2006-06-06 修回日期:2006-07-23 发布日期:2006-12-06
• 通讯作者: 郑旭明 E-mail:zhengxuming126@126.com

### Density Functional Theory Investigation of the Photoisomerization Reaction of Nitroalkanes and Nirroaromatic Compounds

ZHANG Shu-Qiang;WANG Ya-Qiong;ZHENG Xu-Ming

1. (Key Laboratory of Advanced Texile Materials of Ministry of Educations, Department of Applied Chemistry, College of Science, Zhejiang Sci-Tech University, Hangzhou 310018, P. R. China)
• Received:2006-06-06 Revised:2006-07-23 Published:2006-12-06
• Contact: ZHENG Xu-Ming E-mail:zhengxuming126@126.com

Abstract: The geometry structures and the energy barriers for the ground-state isomerization reactions of nitromethane, nitroethylene, nitrobenzene, and trans-β-nitrostyrene were computed using B3LYP/6-31G* level of theory. Their electronic transition energies were obtained using B3LYP-TD/6-31G* calculations. The results indicated that the C—N bond lengths of trans-β-nitrostyrene and nitrobenzen were significantly shorter than that of nitromethane, meanwhile the isomerization energy barriers of trans-β-nitrostyrene and nitrobenzen were somewhat lower than that of nitromethane. The energy difference (ΔE) between the vertical electronic transition energy and the transition state of the ground-state isomerization decreased dramatically with the increase of the molecular unsaturation as the molecule went from trans-β-nitrostyrene to nitrobenzene and to nitromethane. This suggests that as the unsaturation degree of the substituent R increases for R—NO2, the curve crossing between the excited state and the ground isomerization potential energy surface increases and this greatly favors the isomerization exit channel. The calculated first transition-allowed absorption band (also called A-band absorption) was assigned to a π→π* transition for these molecules. While the A-band electronic transition of nitromethane is mainly localized on the NO2 group, those of trans-β-nitrostyrene, nitrobenzene and nitroethylene are largely delocalized over the molecules, which causes the intramolecular charge-transfer processes to take place between the NO2 group and the C6H5—C=C group, the C6H5 group as well as the C=C group. Thus the localization or delocalization of the A-band electronic transition of nitroalkanes or nitroaromatics plays an important role in manipulating its photodissociation channel or photoisomerization channel.