5) For each spectrum below, chose between the alternative compounds. Give your reasons.
5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
3.00 2.07
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
12.5 12.0 11.5 11
0.86
OH O
OH or O
OH OH
or
or
OH OH
or
Homework
Coupling with OH is not always visible, depends on solvent
C H
3CH
3O
Ethyl chloropropionates, which is which?
O
O
CH3 Cl
H3C
O
O
CH3 Cl
H3C
O
O
CH3 Cl
O
O
CH3 Cl
O O H3C
O
O H3C
O
O H3C
O
O
CH3
Information about
1.Coupling partners → Constitution 2.Bond angle → 3D structure!!!
Karplus equation
2J aliphatic 10-16 cis 12
2J sp2 1-2 trans 16
3J aliphatic free rotation
6-7 ortho 7-9
ax-ax 12 meta 2
ax-eq, eq-eq 2-3 para 1
Coupling constants
Lots of experimentally collected values can be find in tables
Non first order spectra!!!
O CH3
N H2
O
Non first order spectra
increasing, the spectrum can change totally First order: 10* J < Δυ
Spin systems named by the letters of alphabet
J / Δυ
AB
ABX
4
5
6
7
N
3
2
S
1 Me
Cl
CHO
1 2 6
3 5
4
OMe
OH
3 4
Acrylnitrile
400 MHz
N H
H
H
Increasing B
0the spectrum gets closer to first order.
Why?
Complicated spin systems: pl. AA ’ BB ’
p - v. o -disubstituted benzene (chemically equivalent but magnetically not equivalent)
p -bromophenol 1,2-dibromobenzene
THF behaves similarly!
Magnetic anisotropy
Neighbouring groups have effect on chemical shift through space as well (not just through chemical bond)
DMF
H N
CH3 O
CH3
Ring positions
2
H
eq2
H
ax3
H
eq+
4H
3
H
axN
H
axH
axH
eqH
axH
eq 24 3
Magnetic anisotropy
Aromatic ring currents
0.8 ppm
2.6 ppm
Metilcsoport: -4.2 ppm H H H H H
H
H H
H H
H H
H
H H
H H H
23 -1,9
8,9
H H H H
H
H
9
H Me
OMe OMe
Me
Me H
OMe OMe
Me
10a 10b
6,68 2,27 2,35
6,40
NMR spectrometer
How to measure?
1. Sample preparation 1. Solvent
2. O2 exemption 3. Filtering
2. Measurement
1. Setting the instrument: tune, lock, shim 2. Parameters
3. Data managment 1. FT
2. Phase correction
3. Baseline correction (BC) 4. Referencing (TMS, solvent) 5. Integral (1H)
(…administrating…)
B
=
2
Is B constant (not taking chemical shift in account)?
NO!
The coil defines H (magnetic field)
B = m H
The magnetic induction ( B ) depends on the material in the magnetic field!!!
Does the material changes in the instrument???
Magnetic permeability
Tuning: RF coils parameters set depending on tube and solvent
YES!!!
Lock: Solvent D signal to maintain B constant
Shimming: magnetic field homogenity
Control: singulet signal (eg. TMS) width
FT
Phase correction
BC
Integration
