introduction to 13c-nmr spectroscopy...introduction to 13c-nmr spectroscopy main topics-13c-atom...
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344 Organic Chemistry Laboratory
Introduction to 13C-NMR Spectroscopy
Main topics
- 13C-atom chemical shift range
-1H-coupled and decoupled 13C-NMR spectra
1
5.946.00
TMS
1H-NMR Spectrum of n-pentane
2
three 1H-atom
environments
8.00
6.00
1H-NMR Spectrum of n-hexane
3
three 1H-atom
environments
40.00
5.91
1H-NMR Spectrum of n-docosane
4
13C is NMR active (I = ½); 12C is NMR inactive (I = 0).
The natural abundance of 13C is ~1.1%.
A greater chemical shift range provides greater better differentiation of signals; reduced 2nd order effects
Often the NMR experiment is performed in a 1H-decoupled manner to simplify the spectrum; removes coupling to H-atoms.
13C-NMR Spectroscopy
5
(~220 ppm)
31.68
22.74
14.14
TMS
77.02
13C-NMR Spectrum of n-Hexane
6
three 13C-atom
environments
CH3OH
1H is > 99% abundant; it couples strongly to 13C –atom it is attached to (1JHC = 100-210 Hz) with normal n+1 rule splitting.
512 scans30 min10 M concentration
CDCl3
CH3OH
13C-NMR Spectrum of Methanol
1H – Decoupled
1H – Coupled
7
CDCl3
CDCl3
CH3CH2OH
CH3CH2OH
CH3CH2OH
CH3CH2OH
13C-NMR Spectrum of Ethanol 512 scans30 min10 M concentration
1H – Decoupled
1H – Coupled
8
13C-NMR Spectroscopy Chemical Shift Ranges
9
sp2 hybridized 13C-atoms sp3 hybridized 13C-atoms
sp hybridized 13C-atoms
Reich, Hans J. http://www.chem.wisc.edu/areas/reich/handouts/chem343-345/345-nmr-handout.pdf
512 scans30 min0.35 M concentration
CDCl3a bc
d
a bc
d
e
e
13C-NMR Spectrum of Ethyl Cyanoacetate
10
11
13C-NMR Spectrum of Ethyl Cyanoacetate
163.08113.31
62.96
CDCl3
24.81 13.99
14.1
Isotropic NMR Shifts relative to TMS calculated with WebMO/Gaussian09 at B3LYP/6-31G(d)
24.0
61.9
62.6
14.0
24.1101.0
155.3
101.3
155.0
12
Determination of 4’-sulfamoylacetanilide Regiochemistry
13
Determination of 4’-sulfamoylacetanilide Regiochemistry
A B C
D E
F