C8953
NMR structural analysis  seminar
Information about classes + 1D 1H-NMR
Michal Knor
437395@mail.muni.cz
March 10, 2021

Information about classes
Credit:
►3 homework tests + final exercise
Study materials:
https://is.muni.cz/auth/el/1431/jaro2021/C8953/um
E-tests:
https://is.muni.cz/auth/el/1431/jaro2021/C8953/odp

Energy levels splitting
β
ΔE
α
B0
E
B0
ms=+1/2
α
ms=‐1/2
β
s=1/2
Nα>Nβ

Behavior of nuclear spin after irradiation by RF pulse
y
x
z
Mz
B0
B0
Bloc
Precession frequency:
Precession frequency affected by nuclear shielding:  Chemical shift:
Definition of th relative scale of the chemical shift:
ω = ‐γB0
ω = ‐(1+σ)B 0
δ = ω ‐ ωref
6
δ = (ω ‐ ωref)/ωref.10 ppm
B0 induces local mag. field
Bloc, which affects against B0
Nuclear shielding

Characteristic intervals of chemical shifts values
Increase of chemical shift
Increase of shielding
Lowerω
12
Higherω
10
8
ppm 6
4
2
0
H
H
H
H
H
H
R
H
O
R
O
H
O
R1
R2
H
H
H H
R             H
R Cl
R
O
H
R
O
H
N
H

Trends in chemical shifts
►Electronegativity, inductive and mesomeric effects of  substituents
►Hybridisation
►Relative position towards the ring, double bond
H
Cl
Cl
H  H
Cl
Cl
Cl   H
2,1 ppm 2,3 ppm 3 ppm  H   H H   H H H
I H Br
3,1 ppm  H H
H Cl H OR H NO2
4,5 ppm  H H
5,3 ppm
7,3 ppm
Substituents with ‐I effect
=N+R >‐N+R >‐NO >‐NR
2 3 2 2
‐SO2R>‐SO3>‐SOR>‐SR
‐F>‐OR>‐NR2>‐CR3
‐F>‐Cl>‐Br>‐I
2
=N>=NR>‐NR
‐C=CH>‐CH=CH2>‐CH2‐CH3
Substituents with +I effects
‐N‐R>‐O‐>S‐
‐C(CH3)3>‐CH(CH3)2>‐CH2CH3>‐CH3
metals

Mesomeric effect
5,29
5,29
6,11
6,52
3,74
3,93
‐M
+M
7,24
6,55
7,08
6,70
+M
8,15
7,55
7,70
‐M
Substituents with ‐M effects
‐F, ‐Cl, ‐Br, ‐I, ‐OH, ‐OR, ‐NH2, ‐NHR, ‐NR2, ‐SH, ‐SR
Substituents with +M effect
‐CH=O, ‐RC=O, ‐C(OH)=O, ‐C(OR)=O, ‐C(NH2)=O, ‐NO2, ‐SO3H, ‐C=N

Spin-spin interaction, J-coupling
H
B0 ‐ Bloc
H H
Nucleus H: spin α    ‐Bn
spin β    +Bn
Bloc
B0 ‐ Bloc + Bn
B ‐ B    ‐ B
0 loc n
H
R
R
R
R
H

Interaction constant J
ωa
ωb
=ωa+1/2J
ωc
=ωa‐1/2J
J=ωb‐ωc
B0

Interaction constant J
– CH2 – CH3
►Multiplicity of the nucleus I with the spin 1/2 is given by:  m = n + 1, n = number of interacting
nuclei with nucleus I
►Intensity of lines in multiplet follows Pascal’s triangle
1
1
1
1
2
1
1 3
3
1
1 4
6
4 1
1 5 10
10
5 1

1D 1H NMR spectrum
3J1 3J2
HO – CH2 – CH3
3J2
3J2
3J2
3J1
3J1
3J1
3J
2
3J2
3J2
3J2
3J2     3J2
3J1      3J1
3J1     3J1

Values of J-constants - trends
R1
R2
H
H
R1
H
H
R2
13C
H
13C

H
13C
H
3JHH = 13 ‐ 18 Hz
5JHH = 7 ‐ 12 Hz
1JCH = 125 Hz
1JCH = 160 Hz
1JCH = 250 Hz
N
NH2
O
N  H
H
H
H
H
2JHH= ‐12,5 Hz
3JHH= 12 Hz
H C
3
H
13C
H
HO
O
2JCH= 3.1 Hz
5JHH= 2 ‐ 3 Hz

Values of J-constants - trends
H
A
B
B
H
H A
H B
H
H
A
3JHH = 7,5 Hz
4JHH = 1,5 Hz
5JHH = 0,7 Hz
X= Li H Cl OMe F
2JHH (Hz) 7,1 2,5 ‐1,4 ‐2,0 ‐3,2

1D 1H NMR spectroscopy
►the fastest measuring, the highest sensitivity
►complicated interpretation in case of more complex  systems
We are looking for:
►position of the signal (ppm)
►multiplicity (2J, 3J, 4J)
►intensity (integral)
►halfwidth
We are considering:
►chemical/magnetic equivalence
►enantiotopicity/diastereotopicity
►averaging of signals (dynamics, chemical exchange)

1D 1H NMR spectrum of methyl-5-acetylsalicylate
2
6
3
4
5 1
H C 7
3 8
9
O O
CH
3
O 10
OH

1D 1H NMR spectrum of methyl-5-acetylsalicylate
2
6
3
4
5
H C  7
3 8
9
O O
1 CH
3
O 10
OH
6
4
3
10
8
Notes:
►two singlets in the spectrum - two  isolated groups in the structure -  CH3 groups; Met-8
neighboring  carbonyl has lowest shift than ester  Met-10
►doublet of doublets (cca 8.0 ppm) -  proton signal splitted by two  neighbors - H-4
►two doublets in interaction with H-4 -  based on the J-interaction: doublet  with larger
J-constant belongs to  close proton - H-3, smaller
J-constant - more distant proton -
H-6

1D 1H NMR spectrum of cinnamic acid
6
5
4 2
3
H O
1 8
7 9  OH
H

1D 1H NMR spectrum of cinnamic acid
6
1
3
5
4
7
9  OH
H     O
8
2      H
2,6
3,5
7
4
8
Notes:
►H-8 - doublet with large coupling, in  range of shifts of protons on double  bond, integral = 1
►H-7 - doublet with the same coupling  like doublet H-8, deshielded due to
-M effect of carboxyl and due to
nearby aromatic ring
►more intensive signal between 7.7  and 7.8 ppm has integral: 3-1=2  protons - H-2,6, symmetrical,
highest  shift due to -M effect of substituent in  ortho position on aromatic ring
►signal with integral = 3 around 7.5  ppm - less intensive signal - only one  proton, highest shift
due to -M effect  of substituent in para position - H-4;  more intensive signal with highest  shift
- H-3,5

Draw approximate 1D 1H NMR spectrum of the  following compound



Draw approximate 1D 1H NMR spectrum of the  following compound
Notes:
►H-2 - meta- and ortho- interaction  with H-1 a H-3 - doublet of doublets
►H-1 - only meta- interaction with H-2
- smaller coupling than H-3 in ortho-
interaction with H-2
►chemical shifts are result of overall  effects of substituents on the  aromatic ring

1D 1H NMR spectrum of ethyl glutarate



1D 1H NMR spectrum of benzyl butyrate



1D 1H NMR spectrum of methyl 2-acetoxy propanoate



1D 1H NMR spectrum of ethyl 4-(methylamino)benzoate



1D 1H NMR spectrum of cartilagineal



1D 1H NMR spectrum



Next session:
1D 13C-NMR spectra