Acta Chimica Sinica ›› 2006, Vol. 64 ›› Issue (1): 61-69. Previous Articles     Next Articles

α-取代甲苯定向硝化的理论研究

陈丽涛*,1,2,肖鹤鸣3   

  1. (1北京师范大学化学系 北京 100875)
    (2浙江工业大学绿色化学合成技术国家重点实验室培育基地 杭州 310014)
    (3南京理工大学化学系 南京 210094)
  • 收稿日期:2005-05-19 修回日期:2005-09-22 出版日期:2006-01-14 发布日期:2006-01-14
  • 通讯作者: 陈丽涛

Theoretical Study on Selectivity for Nitration of α-Substituted Toluene with Nitronium

CHEN Li-Tao*,1,2, XIAO He-Ming3   

  1. (1 Department of Chemistry, Beijing Normal University, Beijing 100875)
    (2 Breeding Base of State Key Laboratory of Green Chemistry-Synthesis Technology, Zhejiang University of Technology, Hangzhou 310014)
    (3 Department of Chemistry, Nanjing University of Science and Technology, Nanjing 210094)
  • Received:2005-05-19 Revised:2005-09-22 Online:2006-01-14 Published:2006-01-14
  • Contact: CHEN Li-Tao

The rate-determining steps of isomeric ortho, meta and para nitrations of benzyl alcohol and benzyl fluoride have been theoretically investigated at B3LYP/6-311G** level. Stationary points of the step involving reactant, transition state and intermediate complexes were successfully located and characterized without any restriction on the internal coordinates. Their molecular geometries, electronic structures, IR spectra, and the FMO symmetries of two initial aromatic compounds and the nitronium ion NO2+ have been studied. The vibrational shifts of C—N and C—H stretches from TS to INT at the rate-determining step of target aromatic nitrations show up that the formation of C—N and the cleavage of C—H are not concerned but stepwise to provide an explanation, on a microscopic scale, for the experimental fact of the absence of kinetic isotopic effect in the nitration process for the first time. Also, the influence of introduced fluorine on the orientation effect was figured by calculating the microscopic and kinetic properties of the rate- determining step of concerned aromatic nitrations. The NO2+ attack to the benzyl fluoride was deactivated because of high electronegativity and strong electron withdrawal of fluorine atom. The activation energy after α-substitution of methyl group by a fluorine atom became higher. Yet the CH2F group was still an ortho-para directive, since the activation energies of ortho and para nitrations were relatively lower than that of meta nitration. Contrarily, the introduction of electron-donating substituent OH onto the methyl accelerated the NO2+ attack. Consequently the stabilization energies of complexes were droped even lower than before the α-substitution occurred. The activation energies of ortho and para nitrations, however, were also quite lower than the energy of meta nitration. Therefore, the CH2OH is an ortho-para directing group. Compared to the ortho, the para position is the most favorable due to the NO2+ to approach, for its low steric hindrance effect and high exothermicity. Attack at ortho, however, became even more crowd since one more O atom has been introduced after the α-substitution onto the methyl group. Hence, the energy of ortho nitro benzyl alcohol complex is higher than the energy of para one.

Key words: benzyl fluoride, benzyl alcohol, α-substitution, substituent effect, rate-determining step