c-13 nmr spectroscopy chm 320 la salle university
TRANSCRIPT
C-13 NMR SpectroscopyCHM 320
La Salle University
C-13 Spectrum ofm-Nitroacetophenone
NO2
CCH3
O
1H NMR Spectrum ofEthylbenzene
CH2CH3
Typical ppm ()Ranges in C-13 NMR
Relaxation Times
Coupling Constants are LargeJ Values measured in Hz
HC CCH2CH2CH2CH3
HC CCH2CH2CH2CH3
CH3CH2OCCH2CCH3
OO
CH3CH2OCCH2CCH3
OO
H2C=C=CHCH2CH2OH
CO2H
NH3C
H3C
CCH3
O
Silverstein, p. 212
Silverstein, p. 215
N
H3C
H3C
CH
OCH3
OCH3
CC
H
NHCCH3
O
H3C
HC
O
CF3COCH3
O
Predicting Chemical Shifts
Predicted Chemical Shifts of Ca and Cb
a
b
Ca = (-2.5) + 4(9.1) + 9.4 + 2(-2.5) + 3(-1.5) + (-8.4) = 25.4 ppm
Cb = (-2.5) + 2(9.1) + 5(9.4) +(-7.2) + (-2.5) = 53.0 ppm
base 4o(1o) 4o(2o)
base 2o(4o) 2o(3o)
2,2,4-Trimethylpentane
53.28, 31.10, 30.16, 25.51, 24.73
Chemical Shift Prediction with Functional Groups
Use Base Value From Table 4.5
OH
OH
OH
Using Table 4.5 and 4.6
34.7 + 41 = 75.7 22.8 + 41 = 63.8 13.9 + 48 = 51.9 ppm
You can Choose Which Base Value from Table 4.5 to Use
OH
OH
34.7 + 41 + (-5) + 3(9.4) + (-2.5) + (-7.2) = 89.2 ppm
C-3 -OH -OH 2o(3o) 2o(4o)
OH
OH
36.9 + 41 + (-5) + 2(9.4) + (-2.5) = 88.8 ppm
C-3 -OH -OH 2o(3o)
Spectrum at 75 MHz and 150 MHz