What are unsaturated hydrocarbons?
Saturated hydrocarbons
• maximum number of hydrogen atoms attached to each carbon atom.
• alkanes and cycloalkanes with single C-C bonds.
CH
3
—CH
2
—CH
3
Unsaturated hydrocarbons
• fewer hydrogen atoms attached to the carbon chain than alkanes.
• alkenes with double bonds.
• alkynes with triple bonds.
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 Hydrocarbons can be aliphatics
 Straight chain
 Alkanes, alkenes and alkynes
 CH
3
—CH
2
—CH
3,
H
2
C=CH ─ CH
3 ,
HC ≡ C ─ CH
3
 Hydrocarbons can be Aromatics
 must have benzene ring

Let’s study aliphatic: alkenes?
The names of alkenes
• use corresponding alkane name.
• Change ending to – ene .
Alkene IUPAC Common
H
2
C=CH
2
H
2
C=CH ─ CH
3 eth ene prop ene ethyl ene propylene cyclohex ene
3

Ethene (Ethylene )
Ethene or ethylene
• alkene with the formula C
2
H
4
.
• two carbon atoms connected by a double bond.
• two H atoms bonded to each C atom.
• flat with all C and H atoms in same plane.
• used to accelerate ripening of fruits.
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How do we name alkynes (aliphatic)?
The names of alkynes
• use corresponding alkane name.
• change ending to – yne .
Alkyne IUPAC Common
HC ≡ CH
HC ≡ C ─ CH
3 eth yne prop yne acetylene
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Look for double or triple bonds carbon chain of an alkene or alkyne has four or more C atoms, number chain to give lowest number to first carbon in double or triple bond.
CH
2
=CH ─ CH
2
─ CH
3
1 2 3 4
CH
3
─ CH=CH ─ CH
3
1 2 3 4
CH
3
─ CH
2
─ C

C ─ CH
3
5 4 3 2 1
1-butene
2-butene
2-pentyne
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Learning check
Write the IUPAC name for each of the following:
1. CH
2
=CH ─ CH
2
─ CH
3
2. CH
3
─ CH=CH ─ CH
3
CH
3
|
3. CH
3
─ CH=C ─ CH
3
4. CH
3
─ C

C ─ CH
3
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Learning check
Write the IUPAC name for each of the following:
A. CH
3
─ CH
2
─ C ≡ C ─ CH
3
CH
3

B. CH
3
─ CH
2
─ C=CH ─ CH
3
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What are cis and trans isomers?
In alkene double bond,
• is rigid.
• holds attached groups in fixed positions.
• makes cis/trans isomers possible.
CH
3
CH = CH cis
CH
3
CH
3
CH = CH trans CH
3
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Possible cis-trans isomers !
Two isomers are possible when groups are attached to the double bond are different.
• cis isomer , groups are attached on same side of double bond.
• trans isomer , groups are attached on opposite sides.
Br Br
Br
C C C C
H H
H
H Br
H Br
H
C C
CH
3
(not cis or trans)
H
C C
Br
(not cis or trans)
H
Br cis1,2-dibromoethene trans1,2dibromoethene prefixes cis or trans are placed in front

Reactions of unsaturated hydrocarbons
In alkene and alkynes (aliphatic)
• double or triple bond easily broken,
• which makes double and triple bonds very reactive.
• reactants are added to carbon atoms in double or triple bond.
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Let’s look at hydrogenation!
hydrogenation ,
• Hydrogen atoms add to carbon atoms of a double bond or triple bond.
• catalyst such as Pt or Ni used to speed up reaction.
• Adding H
2 to double bonds in vegetable oils
• Compounds with higher melting points.
• Solids at room temperature such as margarine, soft margarine, and shortening. some cis double bonds convert
• trans double bonds (more stable)
• cause change in fatty acid
• label states “partially” or “fully hydrogenated
H H
Pt
H
2
C CH
2
+ H
2
H
2
C CH
2
HC CH + 2H
2
Ni
H H
HC CH
H H 12

What are hydration reactions?
addition reaction called hydration,
• acid H + catalyst is required.
• water (HOH) adds to double bond.
• H atom bonds to one C in double bond.
• an OH bonds to other C.
CH
3
─ CH=CH ─ CH
3
+ H ─ OH
H +
H OH
│ │
CH
3
─ CH ─ CH ─ CH
3
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More on hydration!
When hydration occurs with a double bond that has an unequal number of H atoms ,
• H atom bonds to C in double bond with more H.
• OH bonds to C in double bond with the fewer H atoms.
• Rich gets richer rule!
CH
3
─ CH=CH
2
+ H ─ OH
H +
OH H
│ │
CH
3
─ CH ─ CH
2
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Another reaction of unsaturated hydrocarbons!
Polymers are
• large, long-chain molecules.
• found in nature, including cellulose in plants, starches in food, proteins, and DNA in body.
• also synthetic such as polyethylene and polystyrene,
Teflon, and nylon.
• have small repeating units called monomers .
• can be made from reaction of small alkenes.
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Let’s look at polymerization closely!
In polymerization, small repeating units called monomers join to form a long chain polymer.
H
C C
H
+
H H
H
H
C C
H
H
+
H
C C
H
H H
Ethylene monomers monomer unit repeats chain continues
H H H H H H
C C C C C C
H H H H H H
Polyethylene n chain continues
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What are aromatic Compounds?
Benzene is
• an aromatic compound .
• a ring of 6 C atoms and 6 H atoms.
• a flat ring structure drawn with three double bonds.
• represented by two structures because the electrons are shared among all the C atoms.
• has 6 electrons shared equally among the 6 C atoms.
• is also represented as a hexagon with a circle drawn inside.
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Some aromatic compounds in nature and health
Vanillin
O
CH
Aspirin
O
COH O
C O CH
3
OCH
3
OH
Ibuprofen Acetaminophen
O
NH C CH
3
OH
H
3
C
CH
3
CH CH
2
CH
3
CH
O
COH
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Naming aromatic compounds
Aromatic compounds are named
• with benzene as parent chain.
• with one side group named in front of benzene .
CH
3 Cl methyl benzene chloro benzene
20

Some common names
Some substituted benzene rings
• have common names that have been in use for many years.
• with a single substituent use a common name or are named as a benzene derivative.
CH
3
NH
2
OH toluene aniline phenol
(methylbenzene) (benzenamine) (hydroxybenzene)
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Naming aromatic compounds
When two groups are attached to benzene ring, the ring is numbered to give the lowest numbers to the side groups.
CH
3
Cl OH
Cl
Cl
Cl
3-chlorotoluene 1,4-dichlorobenzene 2-chlorophenol
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