双哌啶基二硫化物的动态NMR的研究

双取代哌啶基二硫化物的动态^1H NMR谱的研究表明,分子内哌啶环的翻转活化自由能较哌啶有显著增加,△G值为71.43±0.25-73.27±0.46kJ.mol^-^1,同时观察到双哌啶基二硫化物分子内哌啶环的3,4,5-位所在平面的翻转,比1,2,6-位所有在平面约快四倍,△G值低3.62kJ.mol^-^1;这充分显示了分子中N原子上带有较大基团的影响.比较双哌啶基二硫化物与相应三硫化物的环翻转能垒,也显示出空间障碍的影响.

A study on the kinetic NMR of bispiperidyl disulfides

The study of kinetic NMR on bis-substituted piperidyl disulfides showed that there is a remarkable increase of free energy of activation for the inversion of piperidine ring in comparison with piperidine itself. It was also observed that, within the mol. of bis-substituted piperidyl disulfides, one half of the ring in which the 3,4- and 5-ring atoms are located undergoes inversion about 4 times faster than the other half of the ring, in which the 1,2- and 6-ring atoms are located. This clearly demonstrates the influence of the large substituent group on the N atom of piperidine ring. A comparison of the potential barrier for ring inversion of bispiperidyl disulfides and the corresponding trisulfides shows that the steric hindrance within the disulfide mol. has also some influence upon the ring inversion process.