Download 240 chem Benzen.pps

Introduction
Copyright© 2005, Michael J. Wovkulich. All rights
reserved.
Introduction
C6H6 and was
1. Benzene has the formula _____
Michael _______.
Faraday
discovered in 1825 by _______
This
compound and others like it were called
aromatic
____________
because of its pleasant odor.
Today, the term aromatic refers to the unusual
stability
____________
these compounds possess.
The Structure & Properties of Benzene
1. Draw the structure of benzene Kekulé proposed
in 1866.
H
H
H
C
C
C
C
H
C
C
H
H
2. Experimental evidence shows that all the
carbon-carbon bonds in benzene have the same
bond length. Why is this in disagreement with
Kekulé's structure?
Double bonds are expected to be
shorter than single bonds.
Kekulé's structure should have
alternating short and long bonds.
Draw a better representation of the benzene
structure.
=
The bond order between carbon atoms is
1½
120° and the
_______,
the bond angles are _______,
sp2
carbon atoms are _____-hybridized.
3. The benzene molecule is flat, with the
p
unhybridized _____
orbitals extending above and
below the plane of carbon atoms.
Draw the
benzene ring showing the p orbitals overlapping to
form a continuous ring of orbitals above and below
the plane of carbon atoms.
p orbital
circle of
delocalized
electrons
C
C
C
C
C
C
sp2
framework
p orbital
4. The double bonds in benzene are said to be
conjugated
_______________,
which means that they are
separated by one single bond and overlap their p

orbitals in the _____
bonds. Draw examples of
conjugated and non-conjugated double bonds.
conjugated
non-conjugated
5. Based upon what you've learned about benzene,
are aromatic compounds cyclic or acyclic? Are
they planar or nonplanar?
Do they contain
conjugated or non-conjugated double bonds? Do
they have or lack resonance stability?
6. Draw the structure of cyclooctatetraene.
Using the information in number
compound expected to be aromatic?
5,
is
Yes, it’s expected to be aromatic because it
appears to...
 be cyclic
 be planar
 be conjugated
 have resonance stability
this
Construct a model of cyclooctatetraene. Is this
consistent with your prediction of whether or not
cyclooctatetraene is aromatic? No Why or why not?
In this view,
cyclooctatetraene
appears to be planar,
and could be aromatic.
This view shows that
cyclooctatetraene is
nonplanar, therefore
it cannot be
aromatic.
Cyclooctatetraene...
 is not planar.
 is non-conjugated.
 has no resonance structures.
 is not aromatic.
We need a better set of requirements
for a molecule to be aromatic.
Aromatic, Antiaromatic, & Nonaromatic Compounds
1. A compound is Aromatic if…
cyclic with _________
conjugated pi bonds.
 It is _______
sp
 All the atoms in the ring are _____or
sp2
_____-hybridized.
planar (or nearly) so that it
 It is _________
forms a continuous, overlapping ring of
p
parallel _____
orbitals.
lower energy due to
 It has _______
 electrons.
delocalization of _____
2. A compound is Antiaromatic if…
Numbers , , and  are True, but  is False.
Cyclobutadiene is antiaromatic. Why? Remember
what the polygon rule told us about the stability
of benzene vs. cyclobutadiene.
The polygon rule shows that
cyclobutadiene is expected to
be unstable.
There is no resonance stability.
3. A compound is Nonaromatic if…
Neither the criteria described in number 1 nor
number 2 apply. Cyclooctatetraene is
nonaromatic. Why? Consider whether the four
criteria in number 1 are true or false.
 cyclic, but non-conjugated
 sp2-hybridized carbon atoms
 nonplanar (poor overlap of p orbitals)
 higher energy (polygon rule)
Hückel’s Rule
1. Another way to predict whether a compound is
aromatic or antiaromatic is Hückel's Rule. Before
we can apply this rule, the compound must have a
p
continuous
_______________
ring of overlapping _____
planar
orbitals, usually in a _________
arrangement.
Once these conditions are met, we can use
Hückel's Rule.
2. Hückel's Rule says: If the number of pi
electrons in the cyclic system is…
aromatic
 4N + 2, the system is _________________.
antiaromatic
 4N, the system is _________________.
Where N is an integer.
3. Fill in the table below.
N
Number of Pi Electrons
4N (Antiaromatic)
4N + 2 (Aromatic)
2
0
1
4
6
2
8
10
3
12
14
4. Fill in the table below.
Compound
# Pi
Electrons
N
4N
or
4N + 2?
6
1
4N + 2
Aromatic
4N
Antiaromatic
4N
Antiaromatic
if planar*
4
8
1
2
*COT is nonplanar = nonaromatic
(Hückel’s rule doesn’t apply).
Antiaromatic
or
Aromatic?
5. Fill in the table below.
Compound
# Pi
Electrons
N
4N
or
4N + 2?
10
2
4N + 2
Aromatic
4N
Antiaromatic
4N
Nonaromatic*
8
8
2
2
Antiaromatic
or
Aromatic?
*There is not a continuous ring of overlapping p orbitals
(Hückel’s rule doesn’t apply).
Nomenclature of Benzene Derivatives
1. Although benzene is a stable aromatic
compound, it doesn't mean it's unreactive.
Benzene undergoes many reactions to form useful
derivatives.
Some of the more commonly used
derivatives, shown below, use common names
instead of IUPAC names.
For each compound
below, give the common name and the IUPAC
name.
OH
CH3
NH2
OCH3
phenol
toluene
aniline
anisole
benzenol
methylbenzene
benzenamine
methoxybenzene
O
O
O
H
styrene
acetophenone
vinylbenzene
methyl phenyl
ketone
benzaldehyde
OH
benzoic acid
2. Some benzene derivatives are named by
combining the substituent name with the word
"benzene." Name the following compounds.
NO2
ethylbenzene
isopropylbenzene t-butylbenzene
nitrobenzene
3. When benzene loses one H atom and becomes a
substituent, it forms the C6H5— group and is
phenyl
named _________.
When toluene loses one
methyl H atom and becomes a substituent, it
forms the C6H5CH2— group and is named
benzyl
_________.
Name the following compounds.
O
diphenyl ether
CH2Cl
benzyl chloride
CH2OH
benzyl alcohol
4. Disubstituted benzenes are given common names
by using the prefixes ortho-, meta-, and paraomp(abbreviated _____,
_____,
and _____)
to show
the relative position of the two substituents on
the benzene ring.
Numbers are used by the
1,2IUPAC system. For example, the numbers _____
1,3- indicate meta-, and
indicate ortho-, _____
1,4- indicate para-.
_____
Identify the substitution pattern in each example
below.
X
X
X
Y
Y
Y
ortho- or o-
meta- or m-
para- or p-
1,2-
1,3-
1,4-
5. When there are two methyl groups on the
benzene ring, the molecule is given the common
name xylene. For each compound below, give the
common name and the IUPAC name.
CH3
CH3
CH3
CH3
CH3
CH3
o-xylene
m-xylene
p-xylene
1,2-xylene
1,3-xylene
1,4-xylene
6. For each compound below, give the common
name and the IUPAC name.
Cl
Br
NO2
Br
Br
o-dibromobenzene
1,2-dibromobenzene
m-bromochlorobenzene
P-fluoronitrobenzene
1-bromo-3-chlorobenzene 1-fluoro-4-nitrobenzene
Cl
F
Cl
F
CH2CH3
CH3
OH
o-chloroethylbenzene
m-fluorotoluene
p-chlorophenol
1-chloro-2-ethylbenzene
3-fluorotoluene
4-chlorophenol
7. When there are three or more substituents on
the benzene ring, numbers are used to show their
relative positions. One substituent is often used
to form the base name and this substituent is
assigned number 1. The other substituents are
numbered in the direction that gives the lowest
possible set of numbers.
Name the following
compounds.
NO2
Br
1
1
Br
5
Br
2
3
Br
1,3,5-tribromobenzene
Br
4
Cl
2-bromo-4-chloro1-nitrobenzene
4
2
1
NO2
Cl
4-bromo-1-chloro2-nitrobenzene
OH
1
4
Cl
2
1
Br
5
1
CH3
2
3
HO
4
Cl
NO2
Br
Cl
2,4-dichlorophenol
3-bromo4-chlorophenol
2
I
1
2-ethyl-4-iodoaniline
O2N
1
NH2
4
CH3
COOH
CH2CH3
F
5
3
5-bromo2-nitrotoluene
F
3,5-difluorobenzoic
acid
6
1
2
NO2
4
NO2
2,4,6trinitrotoluene