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对4-氧-2,2,6,6-四甲基哌啶-1-氧自由基在26种不同溶剂中的顺磁共振谱进行了测定,发现超精细分裂常数A_N随溶剂极性的增加而上升,而g值却呈现微小的下降趋势。A_N与Reichardt E_T、Kosower Z值之间有线性关系,而与ε、μ却不呈现线性关系。由于E_T、Z为模型反应的溶剂微观极性效应参数,而ε、μ为非模型反应的溶剂宏观极性效应参数,所以A_N可以作为一种新的非模型反应的溶剂微观极性效应参数。用HMO方法计算了氮氧自由基中异核双原子三电子键(N—O)的成键和反键轨道能量,采用Streitwieser所推荐的杂原子h_i和K_(ij)的半经验数值,结果表明离域能在0.4—0.5β范围,与丁二烯的离域能(NMO法)相当,定性地说明了氮氧自由基的稳定性以及溶剂极性对π电子密度分布的影响。
The paramagnetic resonance spectra of 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl radical in 26 different solvents were determined and it was found that the hyperfine splitting constant A_N varied with the solvent polarity Increased and increased, while the value of g showed a slight downward trend. There is a linear relationship between A_N and Reichardt E_T and Kosower Z values, but no linear relationship with ε and μ. Since E_T and Z are the parameters of the solvent micro-polar effect of the model reaction, and ε and μ are the macro-polar solvent parameters of the non-model reaction, A_N can be used as a new solvent micro-polar effect parameter of non-model reaction. The bond and antibonding orbital energy of heteronuclear diatomic tri-electron bond (N-O) in nitroxide radical were calculated by HMO method. The semi-empirical values of h i and K ij suggested by Streitwieser were used. It is shown that the delocalization energy is in the range of 0.4-0.5β, which is comparable to the delocalization energy of butadiene (NMO method), and qualitatively illustrates the influence of the nitroxide radical stability and solvent polarity on the π electron density distribution.