Chapter ThirteenChapter ThirteenUnsaturated

Hydrocarbons

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Unsaturated Hydrocarbons

• AlkANES– Hydrocarbons in which all of the carbon-carbon bonds

are _____________ bonds

• AlkENES– Hydrocarbons in which at least one of the carbon-

carbon bonds is a ____________ bond

• AlkYNES– Hydrocarbons in which at least one of the carbon-

carbon bonds is a ______________ bond

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Properties of Alkenes and Alkynes

• Similar to those of alkanes– .– .– .

• .

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Alkenes

• Draw the structures of the monounsaturated alkenes with 4, 5, and 6 carbons

• What is the relationship between the number of carbons and the number of hydrogens in these alkenes?– .

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Alkynes

• Draw the structures of the monounsaturated alkynes with 4, 5, and 6 carbons

• What is the relationship between the number of carbons and the number of hydrogens in these alkenes?– .

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Bond Angles in Alkenes and Alkynes

• According to VSEPR theory:– The four groups bonded to

carbon atoms in single bonds are at angles of ____________________

– The three groups bonded to carbon atoms in a double bond are at angles of ______________________

– The two groups bonded to carbon atoms in a triple bond are at angles of _____________________

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→Fig. 13.1 In ethene, the atoms are in a flat rather than a tetrahedral arrangement. Note the shapes using space filling molecular models.

Unsaturated Hydrocarbons cont’d

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σ and π Bonds

• A single bond between 2 carbon atoms is called a sigma (σ) bond.

• The second bond that forms in a double bond is called the pi (π) bond.

• The third bond that forms a triple bond is also called the pi (π) bond.

• There is π bonding in all double and triple bonds between two carbon atoms.

• π bonds are more reactive than sigma bonds.

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Carbon-carbon double bonds Names end in -___________

H2C=CH2

H2C=CH-CH3

Alkenes

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Carbon-carbon triple bonds Names end in _____________

HCCH

HCC-CH3

Alkynes

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Naming

• Step 1:– Name ___________________________.

• Find the longest continuous carbon chain that contains the multiple bond.

• Name that chain with the __________ suffix if it has a double bond.

• Name the chain with the _______ suffix if it has a triple bond.

CH3CH2CH2

CH3CH2CH2

C

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Naming

• Step 2:– Number the carbon atoms.

• Begin numbering _____________________________

CH3CH2CH2

CH3CH2CH2

C

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Naming

• Step 2:– Number the carbon atoms.

• If the multiple bond is the same distance from each end of the molecule, begin _________________________

CH3CHCH CHCH2CH3

CH3

1 2 3 4 5 66 5 4 3 2 1 ???

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Naming

• Step 3:– Use ___________________________________

_________________to designate multiple bond position.

– List the substituents ________________(with numbers to designate position).

CH3CH2CH2

CH3CH2CH2

C12

345

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Naming

• Step 3:– Use “di”, “tri”, “tetra”, etc. to designate _________

_____________________________

CH3CH2CH2

CH3CH2CH2

C12

345

pentene2-ethyl

1-

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Name these alkenes.

CH3CHCH CHCH2CH3

CH3

CH3CH2CH2

CH3CH CHC

CH2 CCH CH2

CH3

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Name These Alkynes

CH C CH3

CH C CH

CH3

CH3

CH3C

C

C

CH3

ClCH3

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Naming cycloalkenes

• Number the double bond ______________.• The first substituent possesses __________

______________________.

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Name these cycloalkenes.

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Write the IUPAC name for each of the following unsaturated compounds:

A. CH3CH2CCCH3

CH3

B. CH3C=CHCH3 C.

Learning Check

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Learning Check

• Draw the structures that correspond to the following names

– 4-methyl-1-hexene– 1,3-cyclohexadiene– 4,4,5-trimethyl-2-heptene– 4-chloro-1-pentyne– 5-fluoro-4-ethyl-2-hexyne

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Isomerism in Alkenes

• Alkenes have many possible structural isomers– Isomers depend not only on the position of the carbons,

but on where the double bond is

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A comparison of structural isomerism possibilities for four- and five-carbon alkane and alkene systems.

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Cis-Trans Isomerism

• Another kind of isomerism exists in alkenes: _____ _________________________________________– .

C CCH3 CH3

H HC C

CH3

CH3H

H

C CCH3 CH3

H HC C

CH3

CH3H

H

Cis Trans

H H HH

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Cis-Trans Isomerism

• Two isomers are possible when groups are attached to the double bond– In a cis isomer, groups are

attached ______________ of the double bond

– In a trans isomer, groups are attached _____________ ______________________ of the double bond.

– Cis-trans isomerism is not possible when ___________ _______________________ _______________________

cis

trans

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Draw the cis and trans isomers of 1-chloro-2-pentene.

trans-1-chloro-2-pentene

cis-1-chloro-2-pentene

• Review: How many hydrogens on each carbon?

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Learning Check

• Determine whether each of the following substituted alkenes can exist in cis-trans isomeric forms. If they can, draw and name them.– 1-chloropropene

– 2-chloropropene

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Learning Check

• Name each, using cis-trans prefixes when needed

C C

BrBr

H H

CH3

C C

CH3H

H

CH3

C C

Cl

H Cl

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Cis-Trans Isomers in Nature

• Insects emit tiny quantities of pheromones, which are chemicals that send messages

• The silkworm moth attracts other moths by emitting bombykol, which has one cis and one trans double bond.

HOCH2(CH2)7CH2

C C

C C

CH2CH2CH3

HH

H

H

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Terpenes---the basis for cholesterol, steroids and many other biologically active compounds

CH2

C

CH3

CHCH2

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Chemical Reactions of Alkenes and Alkynes

• .

• Types of alkene reactions:– .

• .

– .– .

• .

– .– .

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Addition Reactions

• .

– In the process, __________________________ ______________________________________

C CH

HH

H+ HCl

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In an addition reaction, the atoms provided by an incoming molecule are attached to the carbon atoms originally joined by a double bond.

In the process, the double bond becomes a single bond.

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Adds __________________ to each carbon atom of a double bond (catalyst: Pt or Ni)

H H

Ni

H–C=C–H + H2

ethene

Hydrogenation

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Adding H2 to vegetable oils produces compounds with

higher melting points (ie. can convert a liquid to a solid)

Margarines

Soft margarines

Shortenings (solid)

Products of Hydrogenation

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Fatty acids in vegetable oils are omega-6 acids (the first double bond occurs at carbon 6 counting from the methyl group)

A common omega-6 acid is linoleic acid

CH3CH2CH2CH2CH2CH=CHCH2CH=CH(CH2)7COOH

6

linoleic acid, a fatty acid

Unsaturated Fatty Acids

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In vegetable oils, the unsaturated fats usually contain cis double bonds.

During hydrogenation, some cis double bonds are converted to trans double bonds (more stable) causing a change in the fatty acid structure

If a label states “partially” or “fully hydrogenated”, the fats contain trans fatty acids.

Trans Fats

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In the US, it is estimated that 2-4% of our total Calories is in the form of trans fatty acid.

trans fatty acids behave like saturated fatty acids in the body.

Several studies reported that trans fatty acids raise LDL-cholesterol. Some studies also report that trans fatty acid lower HDL-cholesterol

The trans fatty acids controversy will continue to be debated.

Trans Fats

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Inuit people of Alaska have a high fat diet and high

blood cholesterol levels, but a very low occurrence

of atherosclerosis and heart attacks.

Fat in the Intuit diet was primarily from fish such as

salmon, tuna and herring rather than from land

animals (as in the American diet).

Fats and Atherosclerosis

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Fatty acids in the fish oils are mostly the omega-3 type (first double bond occurs at the third carbon counting from the methyl group).

linolenic acid 18 carbon atoms

CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH

eicosapentaenoic acid (EPA) 20 carbon atoms

CH3CH2(CH=CHCH2)5(CH2)2COOH

Omega-3 Fatty acids

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Plaques of cholesterol adhere to the walls of the blood vessels

Blood pressure rises as blood squeezes through smaller blood

vessels

Blood clots may form

Omega-3 fatty acids decrease the “sticking” of blood platelets

(fewer blood clots)

Omega-3 fatty acids can increase bleeding time

Atherosclerosis

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What is the product of adding H2 (Ni catalyst) to 1-butene?

Learning Check

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____________ also add to the carbons in a double or triple bond

H2CCH2 + Cl2

CH3C=CCH2CH3 + 2Br2

Halogenation

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Using Bromination to Test for Double Bonds

• Bromine in water has a reddish brown color• If another compound with a double bond reacts with the bromine,

______________________– The reddish color persists ______________________________

___________________________________________________

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Write the product of the following addition reactions:

CH3CH=CHCH3 + H2

Learning Check

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Hydrohalogenation

• A _________________ is incorporated into the carbons involved in a multiple bond– The _____________ adds to one carbon– The ______________ adds to the other carbon

• Markovnikov’s rule:– .

H3C CH CH2+ H X

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Where does the halide add to these double bonds (alkenes)?

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Hydration

• A ______________ is incorporated into the carbons involved in a multiple bond– The ___________ adds to one carbon– The ___________ adds to the other carbon

• .• .

H3C CH CH2+ H OH

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Learning Check

• Write the products of each reaction

• CH3-CH=CH2 + Cl2

• CH3-CH=CH-CH3 + H2O

• Cyclopentene + H2

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Addition Reactions: Polymers

• Polymers are large molecules built up by repetitive bonding of many smaller molecules called ____________________.

• May have thousands of monomer units in one polymer molecule.

• The monomers are __________

C CH

HH

HRadical Catalyst C

CC

CC

CC

CC

C

HH

HH HH HH HH HH

HH HH HH HH

Synthetic Polymers

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What is the monomer?

Cl Cl Cl

CH3 CH3 CH3

FF

F F

F F

F F

F F

F F

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What is the monomer?

Aromatic Compounds

Aromatic compounds contain _____________.

Benzene has: • .

• .

• Have many properties similar to alkanes

HH

H

H

H

H

H

H

H

H

H

H

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Structure of Benzene: Resonance

• Two resonance structures.• Neither resonance form is correct by itself.• The true structure is a combination.

– .

– .

Benzene Structure

The structure for benzene is also written as one

formula with a circle within the ring to represented the

alternating double bonds.

• The circle shows:

Benzene

structure

Aromatic Compounds in Nature and Health

Many aromatic compounds are common in nature and in medicine.

Aspirin Vanillin

Ibuprofen

COH

O

O

C O CH3

CH

O

OCH3

OH

CH

CH3

COH

O

CH2

CH3

CHH3C

Naming Aromatic Compounds

Aromatic compounds are named,• With ________________ as the parent chain. • Side chains are named:

ClCH3

Naming Aromatic Compounds

When two groups are attached to benzene, the ring is numbered to give _________________ _____________________________________.

(para-chloromethylbenzene)(meta-dichlorobenzene)(ortho-dimethylbenzene)

1,2-dimethylbenzene 1,3-dichlorobenzene 1-chloro-4-methylbenzene

Cl

CH3

Cl

Cl

CH3

CH3

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Naming Aromatic Compounds

• Disubstituted benzenes are named using prefixes:– .– .– .

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Naming Aromatic Compounds

• ortho- (o)• meta- (m)• para- (p)

Br

Br

Br

Br

Br

Br

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Naming Aromatic Compounds

• Some aromatic compounds have common names.

OH

NH2

Some Common Names

Some substituted benzenes use common names.

toluene 3-chlorotoluene phenol

(Methylbenzene) (meta-chloromethylbenzene) (hydroxybenzene) Toluene meta-chlorotoluene phenol

OH

Cl

CH3CH3

Learning Check

Select the correct name for each structure:

1) chlorocyclohexane2) chlorobenzene3) 1-chlorobenzene

1) 1,2-dimethylbenzene2) 1,4-dimethylbenzene3) 1,3-dimethylbenzene

CH3

CH3

Cl

Learning Check

Write the structural formulas for each of the following:

A. 1,3-dichlorobenzene

B. 2-chlorotoluene

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Naming Aromatic Compounds

• Tri- or higher-substituted benzenes. • Number ________________________________• Use ____________________________________.• Name substituents listed __________________. • If any “common named” monosubstituted parent is used

the principle substituent is on ____________

Br

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Naming Aromatic Compounds

NO2O2N

NO2

NO2

ClO2N

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Chemical Reactions of Aromatic Hydrocarbons

• Aromatic compounds can undergo substitution reactions

– Alkylation • .

– Halogenation • .

– Nitration • .

– Sulfonation • .

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Learning Check

• Write the reaction for the bromination of benzene, including the catalyst.

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