Alkenes, Alkynes, and Aromatic Compounds (Chapter 13)

Alkenes, Alkynes, and Alkenes, Alkynes, and Aromatic CompoundsAromatic Compounds

(Chapter 13)(Chapter 13)

Alkenes and AlkynesAlkenes and Alkynes UnsaturatedUnsaturated

contain carbon-carbon double and triple contain carbon-carbon double and triple bond to which more hydrogen atoms can be bond to which more hydrogen atoms can be added.added.

Alkenes: carbon-carbon double bondsAlkenes: carbon-carbon double bonds Alkynes: carbon-carbon triple bonds.Alkynes: carbon-carbon triple bonds.

Naming Alkenes and Naming Alkenes and AlkynesAlkynes

IUPAC nomenclature rules for IUPAC nomenclature rules for alkenes and alkynes are similar to alkenes and alkynes are similar to alkanes. alkanes. Step 1Step 1. Name the parent compound. . Name the parent compound. Find the longest chain Find the longest chain containing containing the double or triple bondthe double or triple bond, and , and name the parent compound by adding name the parent compound by adding the suffix the suffix –ene or –yne–ene or –yne to the name to the name of the main chain.of the main chain.

Step 2:Step 2: Number the carbon atoms in the Number the carbon atoms in the parent chain, beginning at the end nearest parent chain, beginning at the end nearest to the double or triple bond. If the multiple to the double or triple bond. If the multiple bond is an equal distance from both ends, bond is an equal distance from both ends, begin numbering at the end nearer the begin numbering at the end nearer the first branch point. The number indicates first branch point. The number indicates which carbon the multiple bond is AFTER. which carbon the multiple bond is AFTER. (i.e. between 2 and 3 is 2-)(i.e. between 2 and 3 is 2-) Step 3:Step 3: Assign numbers and names to Assign numbers and names to the branching substituents, and list the the branching substituents, and list the substituents alphabetically. Use commas substituents alphabetically. Use commas to separate numbers, and hyphens to to separate numbers, and hyphens to separate words from numbers.separate words from numbers.

Step 4.Step 4. Indicate the position of Indicate the position of the multiple-bond carbon. If more the multiple-bond carbon. If more than one multiple bond is present, than one multiple bond is present, identify the position of each multiple identify the position of each multiple bond and use the appropriate ending bond and use the appropriate ending diene, triene, tetraene, and so forth.diene, triene, tetraene, and so forth. Step 5.Step 5. Assemble the name. Assemble the name.

Naming Alkenes and Naming Alkenes and AlkynesAlkynes

When the carbon chain has 4 or more C When the carbon chain has 4 or more C atoms, number the chain to give the atoms, number the chain to give the lowest number to the double or triple bond.lowest number to the double or triple bond.

1 2 3 41 2 3 4

CHCH22=CHCH=CHCH22CHCH33 1-butene1-butene

CHCH33CH=CHCHCH=CHCH33 2-butene 2-butene

CHCH33CCCCHCCH33 2-butyne2-butyne

General FormulasGeneral Formulas

AlkenesAlkenes CC22HH44

CC33HH66

Alkynes Alkynes CC22HH22

CC33 H H44

Assigning PriorityAssigning Priority Alkenes and alkynes are considered Alkenes and alkynes are considered

to have equal priorityto have equal priority BothBoth a double and a triple bond a double and a triple bond

present present closer to the end of the chain closer to the end of the chain

determines the direction of numbering. determines the direction of numbering. In the case where each would have In the case where each would have

the same position number, the the same position number, the double bond takes the lower number. double bond takes the lower number.

In the name, “ene” comes before In the name, “ene” comes before “yne” because of alphabetization.“yne” because of alphabetization.

Learning CheckLearning Check

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

A.A. CHCH33CHCH22CCCCHCCH33

CHCH33

B. B. CHCH33C=CHCHC=CHCH33 C. C.

CH3

Multiple Double/Triple Multiple Double/Triple BondsBonds

The two carbons and the four atoms The two carbons and the four atoms that make up the double bond in alkenes that make up the double bond in alkenes lie in a plane. lie in a plane.

Unlike carbon-carbon single bonds, rotation Unlike carbon-carbon single bonds, rotation around carbon-carbon double bond is not around carbon-carbon double bond is not possible. possible.

New kind of isomerism is possible for New kind of isomerism is possible for alkenes. Because rotation is not possible alkenes. Because rotation is not possible around carbon-carbon double bonds, there around carbon-carbon double bonds, there are two different kinds of 2-butenes. are two different kinds of 2-butenes. cis-trans isomers.cis-trans isomers.

Cis-Trans IsomerismCis-Trans Isomerism

Methane is tetrahedral, ethylene is Methane is tetrahedral, ethylene is planar, and acetylene is linear as planar, and acetylene is linear as predicted by the VSEPR theory predicted by the VSEPR theory discussed earlier.discussed earlier.

Cis and Trans IsomersCis and Trans Isomers

Double bond is fixedDouble bond is fixed Cis/trans Isomers are possibleCis/trans Isomers are possible

CHCH33 CH CH33 CH CH33

CH = CHCH = CH CH = CH CH = CH

ciscis trans trans CH CH33

In cis isomers, two methyl groups In cis isomers, two methyl groups are close together on the same side are close together on the same side of the double bond. of the double bond.

In trans isomer, two methyl groups are far In trans isomer, two methyl groups are far apart on opposite side of the double bond.apart on opposite side of the double bond.

Both cis and trans isomers have the same Both cis and trans isomers have the same formula and connections between the formula and connections between the atoms but have different three atoms but have different three dimensional structures because the way dimensional structures because the way the groups are attached to the carbons.the groups are attached to the carbons.

Cis-trans isomerism occurs in an alkene Cis-trans isomerism occurs in an alkene whenever each double bond carbon is whenever each double bond carbon is bonded to two different substituent bonded to two different substituent groups. Cis-trans isomerism is not groups. Cis-trans isomerism is not possible if one of the double bond carbons possible if one of the double bond carbons is attached to two identical groups. is attached to two identical groups.

HydrogenationHydrogenation

Adds a hydrogen atom to each Adds a hydrogen atom to each carbon atom of a double bondcarbon atom of a double bond

H HH H H H H H

NiNi

H–C=C–H + H–C=C–H + HH2 2 HH––CC––CC––HH

H H H H

ethene ethaneethene ethane

Products of HydrogenationProducts of Hydrogenation

Adding HAdding H2 2 to vegetable oils produces to vegetable oils produces

compounds with higher melting compounds with higher melting pointspoints

MargarinesMargarines Soft margarinesSoft margarines Shortenings (solid)Shortenings (solid)

Unsaturated Fatty AcidsUnsaturated Fatty Acids

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

A common omega-6 acid is linoleic acidA common omega-6 acid is linoleic acid

CHCH33CHCH22CHCH22CHCH22CHCH22CH=CHCHCH=CHCH22CH=CH(CHCH=CH(CH22))77COOHCOOH

66

linoleic acid, a fatty acid linoleic acid, a fatty acid

TransTrans Fats Fats

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

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

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

TransTrans Fats Fats

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

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

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

The trans fatty acids controversy will The trans fatty acids controversy will continue to be debated. continue to be debated.

Fats and AtheroschlerosisFats and Atheroschlerosis

Inuit people of Alaska have a high fat Inuit people of Alaska have a high fat

diet and high blood cholesterol levels, diet and high blood cholesterol levels,

but a very low occurrence of but a very low occurrence of

atherosclerosis and heart attacks. atherosclerosis and heart attacks. Fat in the Intuit diet was primarily Fat in the Intuit diet was primarily

from fish such as salmon, tuna and from fish such as salmon, tuna and

herring rather than from land animals herring rather than from land animals

(as in the American diet). (as in the American diet).

Omega-3 Fatty AcidsOmega-3 Fatty Acids

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

linolenic acid 18 carbon atoms linolenic acid 18 carbon atoms

CHCH33CHCH22CH=CHCHCH=CHCH22CH=CHCHCH=CHCH22CH=CH(CHCH=CH(CH22))77COOHCOOH

eicosapentaenoic acid (EPA)eicosapentaenoic acid (EPA) 20 carbon atoms 20 carbon atoms

CHCH33CHCH22(CH=CHCH(CH=CHCH22))55(CH(CH22))22COOH COOH

AtherosclerosisAtherosclerosis

Plaques of cholesterol adhere to the walls of Plaques of cholesterol adhere to the walls of

the blood vessels the blood vessels Blood pressure rises as blood squeezes Blood pressure rises as blood squeezes

through smaller blood vessels through smaller blood vessels Blood clots may formBlood clots may form Omega-3 fatty acids decrease the “sticking” Omega-3 fatty acids decrease the “sticking”

of blood platelets (fewer blood clots) of blood platelets (fewer blood clots) Omega-3 fatty acids can increase bleeding Omega-3 fatty acids can increase bleeding

timetime

Name TheseName These

C CCH3

H

CH3

CH2CH3

C CCl

H

CH2

Cl

CH3

Adding HalogensAdding Halogens

Halogens also add to the double bond of Halogens also add to the double bond of an alkene.an alkene.

HH22CCCHCH22 + + ClCl2 2

H2C CH2

Cl Cl

CH3C CCH2CH3 + Br2 CH3C CCH2CH3

Br Br

Br Br

Aromatic Compounds and Aromatic Compounds and BenzeneBenzene

Aromatic compounds contain benzene.Aromatic compounds contain benzene.

Benzene, CBenzene, C66HH6 6 , is represented as a six , is represented as a six

carbon ring with 3 double bonds.carbon ring with 3 double bonds.

Two possible can be drawn to show Two possible can be drawn to show benzene in this form.benzene in this form. H

H

H

H

H

H

HH

H

H

H

H

Aromatic Compounds Aromatic Compounds and the Structure of Benzeneand the Structure of Benzene

In the early days the word In the early days the word aromaticsaromatics was was used to described many fragrant used to described many fragrant molecules isolated from natural sources. molecules isolated from natural sources. Today the term Today the term aromatic aromatic is used to is used to describe benzene like molecules.describe benzene like molecules.

Benzene is a flat, symmetrical molecule Benzene is a flat, symmetrical molecule with the molecular formula Cwith the molecular formula C66HH66..

It has alternating three carbon-carbon It has alternating three carbon-carbon double and three single bonds.double and three single bonds.

Benzene’s relatively lack of chemical Benzene’s relatively lack of chemical reactivity is due to its structure. reactivity is due to its structure.

There are two possible structures There are two possible structures with alternating double and single with alternating double and single bonds.bonds.

Experimental evidence suggest that all six Experimental evidence suggest that all six carbon-carbon bonds in benzene are identical.carbon-carbon bonds in benzene are identical.

The properties, including the above one, of The properties, including the above one, of benzene can only be explained by assuming benzene can only be explained by assuming that the actual structure of benzene is an that the actual structure of benzene is an average of the above two possible equivalent average of the above two possible equivalent structures-known as structures-known as resonanceresonance..

Simple aromatic compounds like benzene are Simple aromatic compounds like benzene are non-polar, insoluble in water, volatile, and non-polar, insoluble in water, volatile, and flammable.flammable.

Unlike alkenes, several aromatic Unlike alkenes, several aromatic hydrocarbons are toxic. Benzene itself is hydrocarbons are toxic. Benzene itself is implicated as a cancer causing chemical.implicated as a cancer causing chemical.

Aromatic Compounds in Aromatic Compounds in Nature and HealthNature and Health

Many aromatic compounds are common in Many aromatic compounds are common in nature and in medicine.nature and in medicine.

COOH

COOCH3

CHO

OCH3

OH

Aspirin Vanillin

CHCOOH

CH3

CH3CHCH2

CH3

Ibuprofen

Naming Aromatic Naming Aromatic CompoundsCompounds

Aromatic compounds are named with Aromatic compounds are named with benzene as the benzene as the parent chain. parent chain. One side group is named in front of One side group is named in front of the name the name benzene.benzene. - No number is needed for mono-substituted - No number is needed for mono-substituted

benzene since all the ring positions are identical.benzene since all the ring positions are identical.

methylbenzenemethylbenzene chlorobenzenechlorobenzene (toluene)(toluene)

CH3 Cl

Naming Aromatic Naming Aromatic CompoundsCompounds

When two groups are attached to benzene, When two groups are attached to benzene, the ring is numbered to give the lower the ring is numbered to give the lower numbers to the side groups. The prefixes numbers to the side groups. The prefixes ortho (1,2), meta (1,3-) ortho (1,2), meta (1,3-) andand para (1,4-) para (1,4-) areare also used.also used.

CH3

CH3

Cl

Cl

Cl

CH3

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

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

Some Common NamesSome Common Names

Some substituted benzene rings also use a Some substituted benzene rings also use a common name. Then naming with additional common name. Then naming with additional more side groups uses the more side groups uses the ortho-, meta-, ortho-, meta-, para-para- system. system.CH3

Cl

CH3 OH

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

Many substituted aromatic compounds Many substituted aromatic compounds have common names in addition to have common names in addition to their systematic names.their systematic names.

Learning CheckLearning Check

Select the names for each structure:Select the names for each structure:

a. Chlorocyclohexanea. Chlorocyclohexaneb. Chlorobenzeneb. Chlorobenzenec. 1-chlorobenzenec. 1-chlorobenzene

a. a. Meta-Meta-xylenexyleneb. b. Meta-Meta-dimethylbenzenedimethylbenzenec. 1,3-dimethylbenzenec. 1,3-dimethylbenzene

Cl

CH3

CH3

Learning CheckLearning Check

Write the structural formulas for each of the Write the structural formulas for each of the following:following:

A. 1,3-dichlorobenzeneA. 1,3-dichlorobenzene

B. B. Ortho-Ortho-chlorotoluenechlorotoluene

New Attached GroupsNew Attached Groups

PhenylPhenyl

BenzylBenzyl

Nitro -NONitro -NO22

2,4,6-trinitrotoluene2,4,6-trinitrotoluene

Benzyl alcohol

4-phenyl-1-butene

Refer to your chart for order of priority!

PCBsPCBs(Polychlorinated Biphenyls)(Polychlorinated Biphenyls)

There are 209 There are 209 varieties of PCBs, varieties of PCBs, known individually known individually as congeners. A as congeners. A congener may congener may have between 1 have between 1 and 10 chlorine and 10 chlorine atoms, which may atoms, which may be located at be located at various positions various positions on the PCB on the PCB molecule. molecule.

PCBsPCBs PCBs are mixtures of man-made PCBs are mixtures of man-made

chemicals with similar chemical chemicals with similar chemical structures. PCBs can range from structures. PCBs can range from oily liquids to waxy solids. Due to oily liquids to waxy solids. Due to their non-flammability, chemical their non-flammability, chemical stability, high boiling point and stability, high boiling point and electrical insulating properties, electrical insulating properties, PCBs were used in hundreds of PCBs were used in hundreds of industrial and commercial industrial and commercial applications including electrical, applications including electrical, heat transfer, and hydraulic heat transfer, and hydraulic equipment; as plasticizers in equipment; as plasticizers in paints, plastics and rubber paints, plastics and rubber products; in pigments, dyes and products; in pigments, dyes and carbonless copy paper and many carbonless copy paper and many other applications. More than 1.5 other applications. More than 1.5 billion pounds of PCBs were billion pounds of PCBs were manufactured in the United States manufactured in the United States prior to cessation of production in prior to cessation of production in 1977.1977.