C8953
NMR structural analysis
seminar
Information about classes + 1D 1H-NMR
Ondˇrej Jurˇcek, Jan Novotný
jurcekondrej@mail.muni.cz,
novotnyjan@mail.muni.cz
February 27, 2019
Information about classes
Credit:
� Max. 2 unexcused absences
� 2 successfully solved tests (midterm and final)
Study materials:
https://is.muni.cz/auth/el/1431/jaro2019/C8953/um
E-tests:
https://is.muni.cz/auth/el/1431/jaro2019/C8953/odp
Energy levels splitting
α
β
B0
E
B0ms=+1/2
α
ms=‐1/2
β
s=1/2
ΔE
Nα>Nβ
Behavior of nuclear spin after irradiation by RF pulse
y
x
z
Mz
B0
B0
Bloc
Precession frequency: ω = ‐γB0
Precession frequency affected by nuclear shielding: ω = ‐(1+σ)B0
Chemical shift: δ = ω ‐ ωref
Definition of th relative scale of the chemical shift: δ = (ω ‐ ωref)/ωref.106
ppm
B0 induces local mag. field
Bloc, which affects against B0
Nuclear shielding
RfpulseB1
Characteristic intervals of chemical shifts values
Increase of chemical shift
Increase of shielding
Higher ω Lower ω
12 10 8 6 4 2 0ppm
H
H
H
H
H
H
R H
O
R O
O
H
R1
R2
H
H
R Cl
HH
R H
R
O
H
R N
O
H
H
Trends in chemical shifts
� Electronegativity, inductive and mesomeric effects of
substituents
� Hybridisation
� Relative position towards the ring, double bond
H I
H H
H Cl
H H
H Br
H H
H OR
H H
Cl Cl
H H
Cl Cl
Cl H
H NO2
H H
3 ppm
5,3 ppm
7,3 ppm
2,1 ppm 2,3 ppm 3,1 ppm 4,5 ppm Substituents with ‐I effect
=N+
R2>‐N+
R3>‐NO2>‐NR2
‐SO2R>‐SO3>‐SOR>‐SR
‐F>‐OR>‐NR2>‐CR3
‐F>‐Cl>‐Br>‐I
=N>=NR>‐NR2
‐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
8,15
7,55
7,70
MM ‐+
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 H H
B0 ‐ Bloc
Bloc
Nucleus H: spin α ‐Bn
spin β +Bn
B0 ‐ Bloc + Bn
B0 ‐ Bloc ‐ Bn
H
R R R R
H
Interaction constant J
ωaωb ωc
=ωa+1/2J =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 1
H NMR spectrum
HO – CH2 – CH3
3J1
3J2
3J2
3J2
3J2
3J1
3J1
3J1
3J2
3J2
3J2
3J2
3J2
3J2
3J1
3J1
3J1
3J1
Values of J-constants - trends
R1
R2
H
H
R1
H
H
R2
C13
H
C13
H
C13
H
3JHH = 13 ‐ 18 Hz 5JHH = 7 ‐ 12 Hz
1JCH = 125 Hz 1JCH = 160 Hz 1JCH = 250 Hz
N
N
NH2
O
H
H
H
H
H
2JHH= ‐12,5 Hz
3JHH= 12 Hz
CH3
H
C
13
H
OH O
2JCH= 3.1 Hz
5JHH= 2 ‐ 3 Hz
Values of J-constants - trends
H
H
A
B B H
H
A
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 1
H 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 1
H NMR spectrum of methyl-5-acetylsalicylate
1
2
6
3
5
4
7
O
CH3
8
9 O
O
CH3
10
OH
1D 1
H NMR spectrum of cinnamic acid
1
2
6
3
5
4
7
8
9 OH
OH
H
Draw approximate 1D 1
H NMR spectrum of the
following compound
1D 1
H NMR spectrum of cartilagineal
Next session:
1D 13C-NMR spectra