Chapter 18
Aromatic Compounds
i>clicker Q: Why is the compound shown not
considered aromatic even though it has 3 double
bonds in conjugation and a 6 membered ring?
I. It is not planar
II. It does not contain 4n+2 pi electrons
III.It does not have a continuous cyclic
system of p orbitals
A. I only
B. II and III
C. I and III
D. III only
i>clicker Q: Why is the compound shown not
considered aromatic even though it has 3 double
bonds in conjugation and a 6 membered ring?
There are 6 pi electrons.
I. It is not planar
But, those electrons must be in
ring of continuously overlapping
p orbitals which are planar.
II. It does not contain 4n+2 pi electrons
III.It does not have a continuous cyclic
system of p orbitals
A. I only
B. II and III
C. I and III
D. III only
sp3
Not
Flat !!
sp3
Not flat
When
4 pi eˉs
= 4n + 2
→n=
half
½
When
6 pi eˉs
= 4n + 2
→n=1
integer
Aromatic Compounds Other Than Benzene
Heteroatoms (atoms other than C or H) can also be part
of an aromatic ring.
Lone Pair
Of the
Nitrogen
If the lone pair is necessary to make it aromatic,
the electrons are not basic.
Favor the
left side
The difference in electron density can also be
observed by viewing the electrostatic potential
maps.
The Preview of Ch 19Electrophilic Aromatic Substitution (EAS)
i>clicker Q: What is the right structure in the box?
sat. Hs
(1~2
ppm)
sat. Hs
by EWG
(2~3
ppm)
sat. Hs
(1~2
ppm)
arom. Hs
(6.5~8 ppm)
sat. Hs
by EWG
(2~3
ppm)
sat. Hs
(1~2
ppm)
arom. Hs
(6.5~8 ppm)
sat. Hs
by EWG
(2~3
ppm)
sat. Hs
(1~2
ppm)
“Aromatic ring = EWG”
True or False ??
arom. Hs
(6.5~8 ppm)
sat. Hs
by EWG
(2~3
ppm)
sat. Hs
(1~2
ppm)
i>clicker Q: What is the right structure in the box?