Chapter 12 Alkenes, Alkynes, and Aromatic Compounds
Compounds with multiple bonds
The most important compound with a triple bond
is ethyne also known as acetylene;
it is used in the oxy acetylene torch.
Bombykol, is another natural product that contains
double bonds. We will examine the structure of
these materials shortly
Compounds of carbon and hydrogen with less tha 2n+ 2 hydrogens other than cyclic
hydrocarbons
Is there any other way of satisfying the octet for carbon in a molecule with a formula
C2H4 or C2H2?
How many groups around each C? 3
(bonding electrons are not considered
to be a group)
H
H
C
::
C
H
H
What’s the geometry?
triangular
How about C2H2?
H
C

C
H
How many groups around each C?
What’s the geometry?
linear
2
ethene or ethylene
What does ethylene have to do with fruit?
A systematic way of naming alkenes and identifying identical structures
1. Locate the longest carbon chain in the molecule that contains the double bonds: this
identifies the parent alkene
2. Identify the points of branching and count the number of carbons in each branch; name
the alkyl branches in the normal way: methyl, ethyl ...
3. Give the double bond the lowest number
4. Identify any stereochemistry
CH2 CH3
H2C
C
CH2
parent:
4 carbons: butene
groups: 2 carbons: ethyl
location: double bond at position 1; ethyl at 2
CH3
2-ethyl-1-butene
no stereochemistry to describe
Are these two compounds the same?
All these formulas for butane are identical
because of rapid rotation about C-C bonds
If the two groups are on the same
side of the double bond, use cis
On opposite sides, use trans
no, rotation about C=C bonds does not occur
CH2-CH3
CH
H2C
CH2
H2C
CH
CH2
parent: cyclohexane
groups: ethyl, chloro
location: 1, 3
Cl
CH2CH3
CH2CH3
Cl
Cl
The solid wedge is used to denote a group sticking out of the plane of the screen
A dotted wedge is used to denote a group sticking out of the plane of the screen
Two groups with the same relative orientation is called cis
Two groups with the opposite relative orientation is called trans
Naming compounds with double and triple bonds
H3C
generic names alkane
alkene
H2C
ethane
CH3
ethene or ethylene
CH2
alkyne
ethyne or acetylene
H
C
C
H
H
H
C
CH3
CH3
H
H
CH3
H
H
H
cis 2-butene
H
H
CH2CH3
1-butene
CH2CH3
trans 2-butene
CH3
H
CH3
H
C
C
C
CH3
2-butyne
C
C
CH2CH3
1-butyne
H
CH2CH2CH2CH3
C
Name the following:
CH3CH2
C
CH
H
CH3
parent:
groups:
location:
nonene
methyl, double bond
3-methyl, 4-double bond
stereochemistry:
trans
trans 3-methyl-4-nonene
H
CH3
C
parent:
groups:
location:
CH
H2C
CH
H2C
CH2
cyclohexene
methyl
1, 3 or 1,2?
shorthand notation
3-methyl-1-cyclohexene or
1-methyl-2-cyclohexene
A pheromone is a chemical messenger emitted
by insects in minute quantities.
Bombykol is emitted by the silkworm moth to
attract other moths and has one cis and one
trans double bond
16 C: hexadecane
2 double bonds diene
alcohol: drop the last e and add ol
(CH2)7 means 7 CH2 groups in a row
stereochemistry: cis and trans
To name this compound we need to know how to name a compound with 16 carbon atoms
How to name compounds with more than one double bond
How to name alcohols and how to designate “stereochemistry” (the arrangement of groups in
space:
trans10, cis 12-hexadecadien-1-ol
Name the following:
Br
Br
C C
A.
H
H
C C
H
CH3
Cl
CH3
C.
C C
H
ethene
bromo
1,2
cis
cis-1,2-Dibromoethene
H
CH3
B.
parent:
groups:
location
stereochemistry
:
Cl
parent:
groups:
location:
stereochemistry:
parent:
groups:
location:
stereochemistry:
butene
double bond
2
trans
propene
chloro
1,1
none
trans-2-Butene
1,1-Dichloropropene
CH3
C
CH3
CH3
CH2
CH2
CH
parent:
groups:
location
stereochemistry:
CH3
CH C
CH2
CH2
parent:
groups:
location
stereochemistry:
CH3
H
H
C
C
C
C
CH2
H
CH3
CH
CH
CH3
2 -methyl-5-isopropyl-1,3-cyclohexadiene
Dill
Anethum graveolens (Umbelliferae)
Dill is a thin, annual originating in the Middle East. Since recorded history it has
been cultivated as a medicinal and aromatic herb. It was spread through Europe
by way of the monasteries. The picture on the left shows a 'broad-leafed' variety,
the original type has completely thready leaflets. The fresh dill leaves and
flowers contain an essential oil whose main component is (-)-alpha-phellandrene
(ca. 60 %).
Draw structures for the following compounds:
1-hexyne
2-methyl-1,7-octadiene
1,2-propadiene
Compounds of carbon with multiple bonds to other elements
Oxygen double bonded to carbon is called a carbonyl group (C=O)
If the carbon of the carbonyl group is attached
to two other carbon atoms the compound is
called a ketone,
An aldehyde contains a carbonyl group
(C=O), which is a carbon atom with a double
bond to an oxygen atom, attached to at least
one hydrogen.
O
Carboxylic acids contain the carboxyl group,
which is a carbonyl group attached to a
hydroxyl group.
O
acetic acid or ethanoic acid
In an ester, the hydrogen on oxygen is
replaced by a carbon atom.
A nitrogen attached to a carbonyl group is called an amide;
the other two groups attached to nitrogen can be either both
carbons, hydrogens or a mix of both carbon and hydrogen
N
A few reactions of unsaturated compounds:
Adding H2 to double bonds in vegetable
oils produces compounds with higher melting
points solids at room temperature, such as
margarine, soft margarine, and shortening.
This makes them less reactive and less prone to
become rancid; rancidness is due to reaction of
the double bonds with oxygen
O
CH3CH2CH2
butyric acid
C
OH
O
CH3CH2CH2
H
O
C
O
CH2OCCH2CH2CH2CH2
CH2
C
O
H
CH3CH2CH2CH2CH
C 2O
CH
H
CH2OCCH2CH2CH2CH2
+H2 (catalyst)
C
C
O
H
CH2CH2CH2CH3
unsaturated triglyceride
CH3CH2CH2
CH3CH2CH2CH2CH
C 2O
CH2OCCH2CH2CH2CH2
CH2
CH
CH2OCCH2CH2CH2CH2
O
CH2
CH2
CH2CH2CH2CH3
saturated triglyceride
Polymers are large, long-chain molecules;
they are found in nature, including cellulose
in plants, starches in food, and proteins and
DNA in the body;
they are also made synthetically, such as
polyethylene and polystyrene, Teflon, and
nylon
they are made up of small repeating units
called monomers that are often alkenes
Teflon
F
CF2CF2CF2CF2CF2
F
Polypropylene
F
CH3
F
H
CHCH2CHCH2CHCH2CHCH2
H
Cl
H
CH3
CH3
CH3
CH3
H
Polyvinyl chloride
CHCH2CHCH2CHCH2CHCH
H
H
Cl
Cl
Cl
Cl
Recycling is simplified by using codes found on plastic items.
Aromatic Compounds
H
C
H
H
H
C
C
C
C
C
H
H
Different ways of representing the molecule benzene
Molecules that contain a benzene ring are often referred to as aromatic compounds,
originally because of their odor
OH
NH2
CH3
methylbenzene (toluene)
aminobenzene (aniline)
OH
H
OH
C
H
H
C
C
C
C
C
CH3
hydroxybenzene (phenol)
H
C
H
H
H
C
C
C
C
C
H
CH2CH2CH3
O
O
C
O
OH
C
O
OCH3
C
C-OH
H
H
C
H
C
C
C
C
C
C
H
OH
C
H
H
OH
C
C
C
C
C
C
C
C
H
C
C
C
H
H
C
H
H
C
H
benzoic acid
H
salicylic acid
methyl salicylate
2-hydroxybenzoic acid
methyl 2-hydroxybenzoate
4-hydroxy-3methoxybenzaldehyde
H
H
benzaldehyde
1-methyl,2,4,6-trimethylbenzene
acetosalicylic acid
C
C
H
H
H
H
C
H
H
H
Cl
H
H
naphthalene
H
H
H
H
H
H
Cl
1,4-dichlorobenzene
benzo[a]pyrene