Aula 10 - Acoplamentos (Parte 2)

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Chemical Shift
– magnetic induction of the pi electrons in an 
aromatic ring (Fig. 13.11)
Anisotropy of Aromatic compounds: in plane and above
CH3
CH3
H
H
H
H
H
H
H
H
H
H
δδδδring���� 8.14-8.64 ppm
δδδδMe���� -4.25 ppm
H H
δδδδring���� 7.27-6.95 ppm
δδδδCH2���� -0.51 ppm
δδδδOUTSIDE���� 9.28 ppm
δδδδINSIDE���� -2.99 ppm
H
H
H
H
H
H
H
H H
H
H
H
H
HH
H
H
H
Anisotropy: Aromatic
Electronic effects
CH2
O
CH3
CH2
+
O-
CH3
Deshielded
O
O
O
H
H
7.10 ppm
COOEt
COOEt
H
H
COOEt
H
H
EtOOC
6.83 ppm6.28 ppm
O
H
H7.71 ppm
6.10 ppm
O
H
H
H
H7.07 ppm 6.38 ppm
6.28 ppm
5.93 ppm
8 7 6 5 4 3
O
12
3
4
5
6
O
7
Electronic effects: conjugation with carbonyl
8 7 6 5 4 3 2
O
1
2
34
56
7.75
6.20
Electronic effects: conjugation with carbonyl
deshielded
Electronic effects: conjugation with heteroatom
OH
H
O+
C-
H
H
SH
H
6.06 ppm
5.48 ppm
S
H H
5.81 ppm
O
H H5.78 ppm
OH
H4.82 ppm
6.22 ppm
shielded
6.5 6.0 5.5 5.0 4.5 4.0 3.5
12
34
O
5
Electronic effects: no conjugation with heteroatom
7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5
12
34
O
5
2.65 2.60 2.55
6.35 6.30 4.95 4.90
shielded
Electronic effects: conjugation with heteroatom
O CH3
8 7 6 5 4 3 2
8.0 7.5
Electronic effects: conjugation with carbonyl
deshielded
deshielded
o
p
m
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5
O
CH3
7.3 7.2 7.1 7.0 6.9 6.8
Electronic effects: conjugation with heteroatom
Shielded
shielded
o
p
m
NH
CH3
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5
7.0 6.5
Electronic effects: conjugation with heteroatom
Shielded
shielded
o
p
m
F
7.5 7.4 7.3 7.2 7.1 7.0 6.9
Cl
7.4 7.3 7.2 7.1
Br
7.6 7.5 7.4 7.3 7.2 7.1
Aromatic: inductive effect and resonance effect
Calculating Shifts 
for aromatic 
compounds
NMR
� Common Aromatic Patterns
6/9/2011 15
ortho
6-10 Hz
para
1-4 Hz
meta
0-2 Hz8-10 Hz
H
H
H
H
H
H
H
H
NMR
� “Activating” and “Deactivating” groups and the impact of 
the changing electron density in the Benzene ring on 
Chemical Shift of ortho, meta, para protons 
6/9/2011 17
Ha Ha’
Hb Hb’
Ha&Ha’Hb&Hb’
2 Amino Protons
The Molecular Ion peak
from Mass Spectrometry 
would have indicated the 
presence of the single 
Chlorine atom and Nitrogen.
� Para Di-Substituted Benzene ring
� Ha & Ha’ have same Chemical Shift
� Hb & Hb’ have same Chemical Shift
� Ha is split into doublet by Hb
� Hb is split into doublet by Ha
� Two sets of peaks produced by relative
electronegativity of Amino & Cl groups
P-Chloroaniline (C6H6ClN)
Hydrogen bond
Aromatic substitution pattern: ortho
8.00 7.90 7.80 7.70 7.60 7.50 7.40
CH3
CH3
O
O
AA’ XX’
Typical spectra for ortho (symmetrical)
8.5 8.0 7.5
Br
N+
O-
O
H
A
H
B
H
C
H
D
Calculated shifts
δHA=8.44 δHB=7.82 δHC=7.31 δHD=8.19 
HA
HB
HCHD
meta bromo nitro benzene
NMR
� “Activating” and “Deactivating” groups and the impact of 
the changing electron density in the Benzene ring on 
Chemical Shift of ortho, meta, para protons 
6/9/2011 21
c
b a
� The Methoxy group is 
moderately activating, 
while the Nitro groups are 
strongly deactivating 
(electron withdrawing) 
� Net effect is to Decrease 
the electron density about 
the ring protons
� The a & b protons are 
Ortho to the strongly 
deactivating Nitro groups, 
thus, they have reduced 
electron density and their 
Chemical Shift is down 
field relative to the “c” 
proton
� All protons interact to 
produce Spin-Spin 
Coupling.
a b c
3H
2,4-Dinitroanisole (C7H6N2O5)
AB-Spectra
AMX C6 H4 O5 N2
I = 6 - 4/2 + 2/2 +1
I = 6
Phenyl = 4 I
NO2 = 1 I
AMX
AFMX
δ
J
C5 H4 N Br
I = 5 – 4/2 – 1/2 +1/2 +1
I = 4 (aromatic ring)