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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
2、 be 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
3、,50,0,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
4、 natural 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
5、谱（最普通）也称宽带去偶 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,Cycloh
6、exanone,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(一强一弱，成对出现） (2)有溶剂峰(固定、可查） (3)有杂质峰，样品不纯 (4)原分子式测定不准确或有耦合的F、P等,举例,偏共振去偶谱,肉桂酸正丁酯的IR、1H NMR、13C NMR,