碳核磁共振谱

1、核磁共振碳谱 13C NMR,12C is not NMR-active I = 0,however,13C does have spin, I = 1/2 (odd mass,Some nucleis nature abundance and sensitivity,13C signals are 6000 times weaker than 1H because,1. Natural abundance of 13C is small (1.08% of all C,2. Magnetic moment of 13C is small,In order for 13C NMR to be

2、a useful technique in structure determination. A vast increase in the signal-to-noise ratio is required,PULSED FT-NMR IS REQUIRED,The chemical shift range is larger than for protons,0 - 200 ppm,The 13C NMR spectra is very simple: a separate, distinct peak is observed for each carbon,200,150,100,50,0

3、,HO-CH2-CH2-CH3,c,b,a,For a given field strength 13C has its resonance at a different (lower) frequency than 1H,1H,1.41 T 60 MHz,2.35 T 100 MHz,7.05 T 300 MHz,for carbon-13,13C,1.41 T 15.1 MHz,2.35 T 25.0 MHz,7.05 T 75.0 MHz,Divide the hydrogen frequency by 4 (approximately,Because of its low natura

4、l abundance (0.0108) there is a low probability of finding two 13C atoms next to each other in a single molecule,13C - 13C,coupling,NO,not probable,13C - 1H,coupling,YES,very common,However, 13C does couple to hydrogen atoms (I = 1/2,丙酮的13-C 谱,四重峰,七重峰,PROTON-DECOUPLED SPECTRA,质子去偶13C NMR波谱（最普通）也称宽带去

5、偶 去掉1H核对13C的自旋偶合，得到分子中不同环境C的简单谱图,a,b,注意：碳谱无积分 对称的碳峰重叠,质子偏共振去偶（部分去偶,只保留与13C直接相连的质子与13C的偶合裂分(n+1,a) 质子去偶谱，(b) 质子偏共振去偶谱,13C 的化学位移,判断方式与氢谱大致相当,分四个区 (1)烷碳区：050ppm (2)取代烷碳区：5080ppm C-O.C-N, C-S等 (3)芳烯区：100150ppm (4)羰基区：150200ppm,2,2-DIMETHYLBUTANE,Bromocyclohexane,Toluene,Cyclohexene,Cyclohexanone,1,2-dichlorobenzene,总 结：13C谱的特点（与1H谱相比较,1、1HNMR提供了化学位移、耦合常数、积分曲线三个重要信息。在13CNMR中，无积分面积,2、13C的化学位移比1H大得多。碳核所处的化学环境稍有差别，谱图就会有区别，所以碳谱能给出更多有关结构的信息,3、由于H的天然丰度大，氢谱中考虑HH耦合。而13C的天然丰度小，不考虑碳之间的耦合，但应考虑CH之间的耦合,碳谱解析,1、求出分子式的不饱和度 2、计算谱线数目(谱线与碳数相等，分子无对称性) 谱线少，分子有对称性。可从峰高判断 谱线多(1) 有异构体(一强一