13.18 carbon-13 nmr - usp · 13.18 carbon-13 nmr . 12c is not nmr-active i = 0 however…. 13c does...
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![Page 1: 13.18 Carbon-13 NMR - USP · 13.18 Carbon-13 NMR . 12C is not NMR-active I = 0 however…. 13C does have spin, I = 1/2 (odd mass) 1. Natural abundance of 13C is small (1.08% of all](https://reader033.vdocuments.net/reader033/viewer/2022042711/5f87f3f4bd599f30594314f0/html5/thumbnails/1.jpg)
13.18 Carbon-13 NMR
![Page 2: 13.18 Carbon-13 NMR - USP · 13.18 Carbon-13 NMR . 12C is not NMR-active I = 0 however…. 13C does have spin, I = 1/2 (odd mass) 1. Natural abundance of 13C is small (1.08% of all](https://reader033.vdocuments.net/reader033/viewer/2022042711/5f87f3f4bd599f30594314f0/html5/thumbnails/2.jpg)
12C is not NMR-active I = 0
however…. 13C does have spin, I = 1/2 (odd mass)
1. Natural abundance of 13C is small (1.08% of all C)
2. Magnetic moment of 13C is small
13C signals are 6000 times weaker than 1H because:
SALIENT FACTS ABOUT 13C NMR
PULSED FT-NMR IS REQUIRED
The chemical shift range is larger than for protons
0 - 220 ppm
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COUPLING TO ATTACHED PROTONS
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The effect of attached protons on 13C resonances
n+1 = 4 n+1 = 3 n+1 = 2 n+1 = 1
C 13
3 protons 2 protons 1 proton 0 protons
H
H
H
C 13
H
H
C 13
H C 13
Methyl
carbon
Methylene
carbon
Methine
carbon
Quaternary
carbon
( n+1 rule applies )
COUPLING TO ATTACHED PROTONS
(J’s are large ~ 100 - 200 Hz)
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ETHYL PHENYLACETATE
13C coupled
to the hydrogens
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DECOUPLED SPECTRA
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ETHYL PHENYLACETATE
13C coupled
to the protons
13C decoupled
from the protons
in some cases
the peaks of the
multiplets will
overlap
this is an
easier spectrum
to interpret
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CHEMICAL SHIFTS OF 13C ATOMS
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Aldehydes
Ketones
Acids Amides
Esters Anhydrides
Aromatic ring
carbons
Unsaturated
carbon - sp2
Alkyne
carbons - sp
Saturated carbon - sp3
electronegativity effects
Saturated carbon - sp3
no electronegativity effects
C=O
C=O
C=C
C C
200 150 100 50 0
200 150 100 50 0
8 - 30
15 - 55
20 - 60
40 - 80
35 - 80
25 - 65
65 - 90
100 - 150
110 - 175
155 - 185
185 - 220
Correlation chart for 13C Chemical Shifts (ppm)
C-O
C-Cl
C-Br
R3CH R4C
R-CH2-R
R-CH3
RANGE
/
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SPECTRA
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WWU Chemistry
Toluene CH3
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Proton-decoupled 13C spectrum of 1-propanol (22.5 MHz)
200 150 100 50 0
1-Propanol
PROTON
DECOUPLED
HO-CH2-CH2-CH3 c b a
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Cyclohexanol
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Cyclohexanone
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Cl
Cla
a
b
b
c
c
1,2-Dichlorobenzene
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1,3-Dichlolrobenzene
Cl
Cl
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1,4-Dichlorobenzene
Cl
Cl
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Exercício
Composto A Composto B Composto C
Fórmula
Molecular
C7H14O C6H14O C5H6N2
Deslocamento
químico
(ppm),
multiplicidade
e quantidade
23, q (2) 11, q (2) 16, t (2)
28, d 23, t (2) 22, t
29, q 44, d 119, s
33, t 65, t
42, t
206, s