Chemical Shift – magnetic induction of the pi electrons in an aromatic ring (Fig. 13.11) Anisotropy of Aromatic compounds: in plane and above H

H H H H CH3 H H dring  7.27-6.95 ppm d  -0.51 ppm CH2 H H CH 3 H H

H H H H

H H H H dring  8.14-8.64 ppm H H d  -4.25 ppm H H Me H H H

dOUTSIDE  9.28 ppm H H

dINSIDE  -2.99 ppm H H Anisotropy: Aromatic Electronic effects Deshielded + H C H2C 2 - O O H C H3C 3 O H H COOEt H COOEt

7.10 ppm O 6.28 ppm 6.83 ppm

H H COOEt EtOOC H O O

O 5.93 ppm H 6.10 ppm H

7.07 ppm H H 6.38 ppm 7.71 ppm H H 6.28 ppm Electronic effects: conjugation with carbonyl

3 O O 7 5 2 1

6 4

8 7 6 5 4 3 Electronic effects: conjugation with carbonyl

O 1 2 deshielded 4 3

6 5

7.75

6.20

8 7 6 5 4 3 2 Electronic effects: conjugation with heteroatom

+ O O H H - C

H H shielded

S S 6.06 ppm H

H H 5.48 ppm H 5.81 ppm

O O 6.22 ppm H

H5.78 ppmH 4.82 ppm H Electronic effects: no conjugation with heteroatom

O 5 4 3

2 1

6.5 6.0 5.5 5.0 4.5 4.0 3.5 Electronic effects: conjugation with heteroatom

O 5 4 3

2 1

shielded 2.65 2.60 2.55

6.35 6.30 4.95 4.90

7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 Electronic effects: conjugation with carbonyl

o m O CH3 p deshielded

8.0 7.5 deshielded

8 7 6 5 4 3 2 Electronic effects: conjugation with heteroatom

H3C O

Shielded

shielded

m o p

7.3 7.2 7.1 7.0 6.9 6.8

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 Electronic effects: conjugation with heteroatom

H3C NH

m o Shielded p shielded

7.0 6.5

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 Aromatic: inductive effect and resonance effect

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 Calculating Shifts for aromatic compounds NMR  Common Aromatic Patterns

5/14/2013 15 H H Ortho 6-10 Hz

H para 1-4 H Hz H meta 0-2 Hz H H 8-10 Hz 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

P-Chloroaniline (C6H6ClN)

Hb&Hb’ Ha&Ha’ Ha Ha’

Hb Hb’ . Para Di-Substituted Benzene ring . Ha & Ha’ have same Chemical Shift . Hb & Hb’ have same Chemical Shift The Molecular Ion peak . Ha is split into doublet by Hb from Mass Spectrometry . Hb is split into doublet by Ha would have indicated the . Two sets of peaks produced by relative presence of the single electronegativity of Amino & Cl groups Chlorine atom and Nitrogen. 2 Amino Protons

5/14/2013 17 Hydrogen bond meta bromo nitro benzene Br

H H B A Calculated shifts

O dHA=8.44 dHB=7.82 dHC=7.31 dHD=8.19 + H N C - H O D

HA HB HD HC

8.5 8.0 7.5 Aromatic substitution pattern: ortho

AA’ XX’ Typical spectra for ortho (symmetrical)

O

CH3 O

CH3

8.00 7.90 7.80 7.70 7.60 7.50 7.40 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

2,4-Dinitroanisole (C7H6N2O5)

3H . The Methoxy group is moderately activating, while the Nitro groups are strongly deactivating (electron withdrawing) . Net effect is to Decrease c the electron density about the ring protons b a . 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 a b c . All protons interact to produce Spin-Spin Coupling.

5/14/2013 21 AB-Spectra AMX C6 H4 O5 N2 I = 6 - 4/2 + 2/2 +1 I = 6 Phenyl = 4 I NO2 = 1 I AMX AFMX C5 H4 N Br I = 5 – 4/2 – 1/2 +1/2 +1 I = 4 (aromatic ring)

d J Aromatic substituent pattern O CH O CH3 3

NO2 NO t 2 J=8.1 t J=1.8 dt J=7.7, 1.5 ddd J=8.1, 2.2, 1.1

8.5 8.0 Aromatic substituent pattern O CH O CH3 3

NO2

NO2

td dd J=7.4, 1.1 ~td dd J=8.1, 0.7 J=8.1, 1.5 J=7.7, 1.5

8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4