碳核磁共振谱.ppt
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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
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