What are unsaturated hydrocarbons?

Saturated hydrocarbons• maximum number of hydrogen atoms

attached to each carbon atom.• alkanes and cycloalkanes with single C-C

bonds. CH3—CH2—CH3

Unsaturated hydrocarbons• fewer hydrogen atoms attached to the carbon

chain than alkanes.• alkenes with double bonds.• alkynes with triple bonds.

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Aliphatic vs Aromatic

Hydrocarbons can be aliphatics Straight chain

Alkanes, alkenes and alkynesCH3—CH2—CH3, H2C=CH─CH3 ,

HC≡C─CH3

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

H2C=CH2 ethene ethylene

H2C=CH─CH3propene propylene

cyclohexene

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Ethene (Ethylene)

Ethene or ethylene• alkene with the formula C2H4.• 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 ethyne acetylene

HC≡C─CH3 propyne

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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.

CH2=CH─CH2─CH3 1-butene 1 2 3 4

CH3─CH=CH─CH3 2-butene

1 2 3 4

CH3─CH2─CC─CH3 2-pentyne 5 4 3 2 1

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Learning check

Write the IUPAC name for each of the following:

1. CH2=CH─CH2─CH3

2. CH3─CH=CH─CH3

CH3

|3. CH3─CH=C─CH3

4. CH3─CC─CH3

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Learning check

Write the IUPAC name for each of the following:

A. CH3─CH2─C≡C─CH3

CH3

B. CH3─CH2─C=CH─CH3

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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.

CH3 CH3 CH3

CH = CH CH = CH

cis trans CH3

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Possible cis-trans isomers !

Two isomers are possible whengroups are attached to thedouble bond are different.• cis isomer, groups are attached on same

side of double bond. • trans isomer, groups are attached on

opposite sides.

cis-1,2-dibromoethene trans-1,2-dibromoetheneC C

H Br

H CH3

C C

H Br

BrH

(not cis or trans)(not cis or trans)

C C

Br H

BrH

C C

Br Br

H H

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 H2 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

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HC CH + 2H2Ni

HC CH

H H

H H

H2C CH2

H HPt

H2H2C CH2 +

Let’s look at hydrogenation reaction

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. H

OH H+ │

│CH3─CH=CH─CH3 + H─OH

CH3─CH─CH─CH3

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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!

OH H H+ │ │CH3─CH=CH2 + H─OH CH3─CH─CH2

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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.

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chain continues chain continues

Polyethylene

Ethylene monomers

C C C C C C

H H

HH

H

H

H

H

H

H

H

H

++ C C

H H

HH

C C

H H

HH

C C

H H

HH

monomer unit repeats

n

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 Aspirin

Ibuprofen Acetaminophen

COH

O

O

C O CH3CH

O

OCH3OH

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CH

CH3COH

O

CH2

CH3CHH3C

OH

NH

O

C CH3

Naming aromatic compounds

Aromatic compounds are named• with benzene as parent chain. • with one side group named in front of

benzene.

methylbenzene chlorobenzene

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ClCH3

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.

toluene aniline

phenol (methylbenzene) (benzenamine)

(hydroxybenzene)

NH2 OHCH3

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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.

3-chlorotoluene 1,4-dichlorobenzene 2-chlorophenol

OHCH3

Cl

Cl

Cl

Cl

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