A series of amides of piperidin were synthesized and used for studies on the partial double-bond feature of the amide bonds. 1H and 13C NMR spectra of 2-(3, 5-dinitrophenyl)-1-(piperidin-1-yl) ethanone (compound 1) were acquired at various temperatures. The results showed that the C-N bond of the piperidin amides exhibited partially double-bond character at 20 ℃ (293 K) , suggesting that the chemical shifts of a and b, c and d in compound 1 were very different due to the two rotameric states. With increasing temperature, the two peaks of non-equivalent -CH2- groups collapsed into one peak due to the fast rotation of the C-N bond. The rate constant for the dynamic process detected for compound 1 was 380 s-1, and the free energy of activation for compound 1 at coalescence temperature (343 K) was 67 kJ·mol-1.%合成了一系列六氢吡啶酰胺化合物以研究酰胺键的双键性质.采用1H 及 13C NMR 技术确证了不同取代的酰胺化合物中酰胺键的双键性质.进一步采用变温核磁共振技术对2-(3,5-dinitrophenyl)-1-(piperidin-1-yl)ethanone(化合物1)进行了1H 及 13C NMR研究.结果表明,在20 ℃(293 K)时,a,b及c,d上的氢和碳原子具有不同的化学位移,且距酰胺键越近,化学位移的差异越大.随着温度的升高,两种异构体的转换速率增加,酰胺双键的性质越来越不明显,导致化学位移的差异逐渐减小,直至融合为一个峰.经计算,在融合温度下两种异构体的相互转换的速率常数是380 s-1,能垒约为67 kJ·mol-1.
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