C8953
NMR structural analysis - seminar
1D 13C-NMR
Michal Knor
437395@mail.muni.cz
March 17, 2021
1

1H vs 13C NMR
1H
13C
Spin number
1
2
1 2
H: s=   × H: s=1
13
2
1 12
C: s=   ×   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
C
×
T1 relaxation [s]
1-20
1-40
Homonuclear J-interaction
C
×
H↔C J-interaction (∼ 100-250 Hz)
carbon satellites
(n + 1) splitting × decoupling
2

1H vs 13C NMR
1H
13C
Spin number
1
2
1 2
H: s=   × H: s=1
13
2
1 12
C: s=   ×   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
C
×
T1 relaxation [s]
1-20
1-40
Homonuclear J-interaction
C
×
H↔C J-interaction (∼ 100-250 Hz)
carbon satellites
(n + 1) splitting × decoupling
1H-13Cα
1H-13Cβ
1H-12C
ωC-0.51JHC
ωC+0.51JHC
1JHC
1JHC
1D 1H NMR
1D 13C NMR
3
1Hα-13C 1Hβ-13C
1H decoupled

Important regions of 13C 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
50
0.0
100
ppm(δ)
Alkenes
Alkynes
4

1JCH depends on the bond order ( hybridization ⇔
c.haracter )
►-C-H 1JCH  ≈ 125 Hz
►  =C-H 1JCH  ≈ 160 Hz
►≡C-H 1JCH  ≈ 250 Hz
►X-C-H
)   X = N, O, S, F, Cl, . . . 1JCH  ⇑
)   X = Li, Mg, . . . 1JCH  ⇓
2JCH  < 0 or close to zero (<3 Hz)
►often not observable
in 1D 13C H-C interaction suppressed by DECOUPLING
⇒ simplification of spectra (splitting removed, sensitivity)
►saturation of 1H energy levels during decoupling enhances  relatively intensity of 13C signals
because of heteronuclear  nOe ⇒ quaternary carbons usually less intensive.
5

Values of chemical shift of important solvents
Abbr. Formula 1H
13C
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
-
EXPLAIN effect of solvent on the position of residual 1H water  signal:
CHCl3 - 1.6, ACN - 2.1, DMSO - 3.3, MeOH - 4.9
6

How many 13C signal would you expect in the NMR  spectrum?
Ru
N
N
Cl
S
3
Cl  CH
CH3
Cl
O
N
N+  H
7

How many 13C signal would you expect in the NMR  spectrum? 7
Ru
N
N
Cl
S
3
Cl  CH
CH3
Cl
O
N
N+  H
8

1D 13C-NMR 1, bottom without CPD
9


1D 13C-NMR 1, bottom without CPD
Notes:
►numbers at top of peaks  refers to values JHC  constants
►C1+C7 connected to  electronegative groups  (C1 quaternary)
►C2 ipso aromatic, C4+C6
shielded by M+ of OH
►C5+C4 NOE-enhanced in  bit larger extend by close  H
►C9→C12: decaying effect  of N8
10

1D 13C-NMR 2
►ZOOM of coupled region  of most deshielded signals
►coupled spectrum
►spectrum with decoupling
11

1D 13C-NMR 2
Notes:
►C7 carbonyl, C1 attached  to N
►C3/5 deshielded by M-  CO, C2/6 shielded by M+  of NH2
►C4 last quaternary  aromatic signal (most  isolated from H nuclei)
►C9 effect of esteric group,
? C10 affected by NH  exchange
►C12/C14 + C13/C15
decaying effect of N+
12

1D 13C-NMR 3, b - zoom of right region, a - full decoupled spectrum
13


1D 13C-NMR 3, b - zoom of right region, a - full decoupled spectrum
Notes:
►C3/C4 quaternary  aromatic deshielded by O,  Cβ quaternary coupled by  CH3 and CαH
►Cα deshielded by NO2
►C1 last quaternary  aromatic signal
►C2/C6 coupled mutually  and with Cα, C5 isolated  (contraintuitive)
►quartets OMe, Cγ
14

1D 13C-NMR 4, consider equilibrium minor-major form
Which form dominates and why?
15

1D 13C-NMR 4, consider equilibrium minor-major form
Which form dominates and why?
16

17
Draw structural formula of compound with summary formula C9H11NO2 (use 1D 13C NMR spectrum to find
the right structure)

18
Draw structural formula of compound with summary formula C9H11NO2 (use 1D 13C NMR spectrum to find
the right structure)
1
7
1
2
3
4
5
6
7
4
3
2
6
5
Notes:
►C1 quaternary carbonyl, C7 attached to N
►C5 aromatic,deshielded by NH2, shielded by carbonyl group, C6 opposite effects
►C2/C3 decreasing effect of O
►C4 last quarternaty carbon

19
Draw structural formula of compound with summary formula C7H9NO (use 1D 13C NMR spectrum to find
the right structure)

20
Draw structural formula of compound with summary formula C7H9NO (use 1D 13C NMR spectrum to find
the right structure)
Notes:
►C1 quaternary deshilded by O, 5 quarternary deshilded by N
►C3 aromatic,deshielded by OCH3 and NH2
►C2/C4 shielded by OCH3 and NH2 ,OCH3 shielding effect stronger
►C6 shielded by both OCH3 and NH2
►C7 isolated CH3 carbon
1
2
3
4
5
6
7
7
1
5
6
2
4
3

Next topic
Vector Model + 13C APT experiment
21