C8953
NMR structural analysis - seminar
1D 13C-NMR
Jan Novotny
176003@mail.muni.cz
February 28, 2024
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 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
in 1D 13
C 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.
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
How many 13
C signal would you expect in the NMR
spectrum? 6
Ru
N
N
N
N
Cl Cl
Cl
S CH3
CH3
O
N+
-
N
H
1D 13
C-NMR 1, bottom without CPD
1D 13
C-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
1D 13
C-NMR 2
▶ ZOOM of coupled region
of most deshielded signals
▶ coupled spectrum
▶ spectrum with decoupling
1D 13
C-NMR 2
Notes:
▶ C7 carbonyl, C1 attached
to N
▶ C3/5 deshielded by MCO,
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+
1D 13
C-NMR 3, b - zoom of right region, a - full decoupled spectrum
1D 13
C-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
1D 13
C-NMR 4, consider equilibrium minor-major form
Which form dominates and why?
1D 13
C-NMR 4, consider equilibrium minor-major form
Which form dominates and why?
Next topic
Vector Model + 13C APT experiment