12 C is not NMRactive no magnetic spin I 0 13 C has a magnetic spin I 12 odd mass 13 C signals are 6000 times weaker than 1 H because ID: 534975
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Slide1
Carbon-13
12C is not NMR-active (no magnetic spin (I = 0)) 13C has a magnetic spin (I = 1/2 , odd mass)13C signals are 6000 times weaker than 1H because:Natural abundance of 13C is small (1.08% )Magnetic moment of 13C is smallThe gyromagnetic constant of 13C is one-fourth of that of 1HThe chemical shift range is larger than for protons0 - 200 ppmThe number of different signals indicates the number of different kinds of carbonPULSED FT-NMR is required
13C g = 6.72 1H g = 26.75
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Coupling Constants
However, 13C does couple to hydrogen atoms (I = 1/2)13C - 13C
coupling
NO!
not probable
very common
13
C
–
1
H
coupling
YES!
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Coupling to attached Protons
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Decoupling the Proton Spins
Off-resonance decoupling
Proton-Decoupled Spectra
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Ethylphenylacetate
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Some Instruments Show The Multiplicities of
The Peaks on The Decoupled Spectras = singlet t = tripletd = doublet q = quartetCODE :7Slide8
Hydrogen and Carbon Chemical Shifts
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Correlation chart for
13C Chemical Shifts (ppm)9Slide10
Approximate Chemical Shift Ranges (ppm) for Selected Types of Carbon.
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1-Propanol
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2,2-Dimethylbutane
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Bromocyclohexane
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Cyclohexanol
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Cyclohexene
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Cyclohexanone
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Toluene
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a
a
b
b
c
c
1,2-Dichlorobenzene
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1,3-Dichlorobenzene
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Estimation of Carbon Chemical shifts in Substituted Benzene
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