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C has 1.1 % natural abundance
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C NMR
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C NMR is not very sensitive!
C - 13C spin-spin splitting is never observed
almost no molecules have $ 2 13C in them:
for example, the probability of hexane having two adjacent 13C is
0.011 x 0.011 x 0.29 = 3.5 x 10 -6
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C NMR is a carbon counter
tells you the number of chemically nonequivalent carbons
carbons appear in a
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0 - 200 ppm region
C NMR spectra normally are not integrated
peak intensities can be used to guess the “type” of carbon:
usually, CH3 > CH2 > CH > C
< DEPT
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C NMR spectrum
tells you the number of chemically nonequivalent CH 3 , CH2 , and CH carbons
C do not appear–they must be identifed by comparison with the normal 13C NMR spectrum
ways to present a DEPT 13C NMR spectrum:
Q (13C NMR spectrum) + (DEPT-90) + (DEPT-135)
(all carbons) + (only CH carbons) + (CH and CH3 carbons up, CH2 carbons down)
this is the textbook’s method
Q (13C NMR spectrum) + (CH3 subspectrum) + (CH2 subspectrum) + (CH subspectrum)
+ (all protonated carbons subspectrum)
Q
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C NMR spectrum with CH3 , CH2 , CH , and C resonances labeled
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C NMR methanol
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C NMR ethanol
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C NMR ethyl acetate
BASIC 13C NMR CHEMICAL SHIFTS
C Type
Approximate *, ppm
Alkanes
Methyl
Methylene
Methine
Quaternary
0 - 30
15 - 55
25 - 55
30 - 40
Alkenes
C= C
80 - 145
Alkynes
C /C
70 - 90
Arenes
Benzene
110 - 170
128.7
Alcohols and Ethers
C–O
50 - 90
Amines
C–N
40 - 60
Halogens
C–F
C–Cl
C–Br
C–I
70 - 80
25 - 50
10 - 40
-20 - 10
Car bonyls
R 2C= O
RXC= O (X = O or N)
190 - 220
150 - 180
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C NMR of a tribromobenzene, C6H3Br3
What’s the structural formula?
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C NMR of 1,3,5-tribromobenzene
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C NMR spectrum of a chloropentane
Use of DEPT 13C NMR to identify chloropentane structural isomers
A
C5H11Cl
Use of DEPT 13C NMR to identify chloropentane structural isomers
CH2
CH2
CH2
CH3
CH2
A
C5H11Cl
Use of DEPT 13C NMR to identify chloropentane structural isomers
CH2
CH
CH3
CH2
B
C5H11Cl
CH3
Use of DEPT 13C NMR to identify chloropentane structural isomers
CH2
CH2
CH3
CH3
C
C5H11Cl
CH
Use of DEPT 13C NMR to identify chloropentane structural isomers
CH3
CH2
D
C5H11Cl
CH3
C
Use of DEPT 13C NMR to identify chloropentane structural isomers
CH3
E
C5H11Cl
CH2
C