C8953
NMR structural analysis - seminar
1D 13C-NMR
Jan Novotný
novotnyjan@mail.muni.cz
March 9, 2016
Assign labelled 1
H resonances of the molecule:
Diastereotopicity1
1
http://www.chem.wisc.edu/areas/reich/chem605/
Determine the number of nonequivalent 1
H signals :
1
H vs 13
C NMR
1
H 13
C
Spin number 1
H: s=1
2
× 2
H: s=1 13
C: s=1
2
× 12
C: s=0
Abundance [%] 99.98 1.1
Gyromagnetic ratio [107
rad.T−1
.s−1
] 26.8 6.7
Chemical shift range [ppm] 0 - 15 0 - 200
Nuclear shielding σdia σdia + σpara
Integration of signals ×
T1 relaxation [s] 1-20 1-40
Homonuclear J-interaction ×
H↔C J-interaction (∼ 100-250 Hz) carbon satellites (n + 1) splitting × decoupling
1
H-13
Cα 1
H-13
Cβ
1
H-12
C
ωC-0.51
JHCωC+0.51
JHC
1
JHC
1
JHC
1D 1
H NMR
1D 13
C NMR
1
Hβ-13
C1
Hα-13
C
1
H decoupled
Important regions of 13
C chemical shifts
Aldehydes RCH=O
Ketones R1R2C=O
Carboxylic acids R-CO2H
Esters R-CO2R'
Amines R-CONR2'
C-NO2
C-F C-Cl
C-Br
C-I
C-H Saturated Hydrocarbons
C-NH2
C-OH C-SR
C-OR C-Ar
C-SO2 R
C-CO R
C-C=C
C CR
RC N
Heteroaromatics
Aromatics
R2C=CH2
RHC=CHR
R2C=CH2
200 150 100 50 0.0
ppm(δ)
Alkenes
Alkynes
1
JCH depends on the bond order ( hybridization ⇔
s-character )
-C-H 1JCH ≈ 125 Hz
=C-H 1JCH ≈ 160 Hz
≡C-H 1JCH ≈ 250 Hz
X-C-H
X = N, O, S, F, Cl, . . . 1
JCH ⇑
X = Li, Mg, . . . 1
JCH ⇓
2
JCH < 0 or close to zero (<3 Hz)
often not observable
Values of chemical shift of important solvents
Abbr. Formula 1
H 13
C
ACN CH3CN 1.9 118
Benzene C6H6 7.2 128
CHCl3 7.2 77
DCM CH2Cl2 5.3 54
DMF (CH3)2NCHO 2.9, 8.0 32, 163
DMSO (CH3)2SO 2.5 40
MeOH CH3OH 3.3, 4.8 49
Water H2O 4.8 Effect
of solvent on the position of residual 1H water signal:
CHCl3 - 1.6, ACN - 2.1, DMSO - 3.3, MeOH - 4.9
How many 13
C signal would you expect in the NMR
spectrum?
Ru
N
N
N
N
Cl Cl
Cl
S CH3
CH3
O
N+
-
N
H
Assign correct value of chemical shift to labelled NMR
active atoms1
:
1
http://www.chem.wisc.edu/areas/reich/chem605/
Draw the estimate of 13
C NMR spectrum (with and
without 1
H decoupling):
1D 13
C-NMR 1
1D 13
C-NMR 2
1D 13
C-NMR 3