Acta Phys. -Chim. Sin. ›› 2009, Vol. 25 ›› Issue (09): 1785-1790.doi: 10.3866/PKU.WHXB20090833

• ARTICLE • Previous Articles     Next Articles

N—N Rotational Barriers in N’-arylideneacetohydrazide and Molecular Conformation

YUAN Xian-Rui, SHANG Zhen-Hua, LI Run-Yan, LIU Ying-Hua, CHEN Xiao-Xia, ZHANG Hui-Li, XIU Yong   

  1. The Analytical &|Testing Center of Hebei Province, Shijiazhuang 050018, P. R. China|College of Chemical and Pharmaceutical Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, P. R. China
  • Received:2009-01-12 Revised:2009-06-04 Published:2009-09-03
  • Contact: LIU Ying-Hua E-mail:kdlyh@hebust.edu.cn

Abstract:

A molecular conformation study of N'-arylideneacetohydrazide compounds was performed using dynamic NMR (DNMR) spectroscopy and density functional theory (DFT). Three groups of double peak patterns in the 1H NMR spectra were observed, which was the result of rotational hindrance of the N—N bond. The difference in the chemical shift of these peaks decreased with increasing temperature. The exchange rate constants were obtained through simulation of the relationship between the difference in chemical shift and temperature. The energy barriers for rotation of the N—N bond were calculated according to Eyring's equation. A model of coexisting E and Z forms of the N—N bond has been suggested to explain the separation of the NH protons in the NMR spectrum. DFT were carried out to optimize the conformational isomers with minimum energies. Peak separations in the methyl and azomethine signals were also found to originate from the rotation hindrance of the N—N bond. After N'-acylideneacetohydrazides were converted to 1,3,4-oxadiazole compounds, the proton signal of the methyl group appeared as a single peak.

Key words: Density functional theory, N”-arylideneacetohydrazide, Dynamic nuclear magnetic resonance, Rotation barrier, Conformation isomer

MSC2000: 

  • O641