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CHAPTER 11CHAPTER 11

An Introduction to Organic Chemistry An Introduction to Organic Chemistry

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ORGANIC CHEMISTRYORGANIC CHEMISTRYORGANIC CHEMISTRYORGANIC CHEMISTRY

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Types of Organic Types of Organic CompoundsCompounds Vast majority of over 20 million known

compounds are based on C: organic organic compounds.compounds.

Generally contain C and H + other elements (O, N, S, Cl, F, Br, I, P, etc.)

Great variety of compounds

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IsomerismIsomerism IsomersIsomers: : compounds thatcompounds that have identical have identical

composition but different structurescomposition but different structures Two forms of isomerismTwo forms of isomerism

Constitutional (or structural)Constitutional (or structural) StereoisomerismStereoisomerism

ConstitutionalConstitutional Same empirical formula but different atom-to-Same empirical formula but different atom-to-

atom connectionsatom connections StereoisomerismStereoisomerism

Same atom-to-atom connections but different Same atom-to-atom connections but different arrangement in space.arrangement in space.

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Structural IsomersStructural Isomers

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Cis-2-buteneCis-2-butene

Stereoisomers: GeometricStereoisomers: Geometric

Geometric isomers can occur when there is a C=C double bond.

Trans-2-buteneTrans-2-butene

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Optical isomersOptical isomers are molecules with non- are molecules with non-superimposable mirror images.superimposable mirror images.

Such molecules are called Such molecules are called CHIRALCHIRAL Pairs of chiral molecules are Pairs of chiral molecules are

enantiomersenantiomers.. Chiral molecules in solution can rotate the Chiral molecules in solution can rotate the

plane of plane polarized light.plane of plane polarized light.

Stereoisomers: OpticalStereoisomers: Optical

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Chiral Compounds—Polarized Chiral Compounds—Polarized LightLight

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Stereoisomers IsomersStereoisomers Isomers

Chirality Chirality generally occurs generally occurs when a C atom when a C atom has 4 different has 4 different groups attached.groups attached.

Lactic acid

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Alkanes have the general formula CAlkanes have the general formula CnnHH2n+22n+2

CHCH44 = methane = methane

CC22HH66 = ethane = ethane

CC33HH88 = propane = propane

CC44HH10 10 = butane= butane

CC55HH1212 = pentane = pentane

HydrocarbonsHydrocarbons

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Alkanes are colorless gases, liquids, and Alkanes are colorless gases, liquids, and solidssolids

Generally unreactive (but undergo Generally unreactive (but undergo combustion)combustion)

Not polar (or low polarity) and so are not Not polar (or low polarity) and so are not soluble in water.soluble in water.

Hydrocarbons: AlkanesHydrocarbons: Alkanes

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Chapter 11 Introduction to Organic Chemistry: Alkanes

10.3

Alkanes with Substituents

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Isomers of Butane

Isomers• have the same

molecular formula.

• have different atom arrangements.

• of butane (C4H10) are a straight chain and a branched chain.

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Alkyl groups

Alkyl groups are• alkanes that are missing one H. • substituents attached to carbon chains.• named with a –yl ending. H

H C CH3 methyl

H H H

H C C CH3 CH2 ethyl H H

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Naming Substituents

In the IUPAC system,• a carbon branch is

named as an alkyl group.

• halogen atoms are named as halo.

TABLE 10.6

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Alkanes with Substituents

CH3

CH3 CH CH3 methylpropane

methyl groups

CH3 CH3

CH3 CH CH2 CH CH3 2,4-dimethylpentane

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Naming Alkanes

Give the name of CH3 CH3

CH3─CH─CH─CH3

STEP 1 Name the longest continuous chain. CH3 CH3

CH3─CH─CH─CH3

butane

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Naming Alkanes

Give the name of CH3 CH3

CH3─CH─CH─CH3

STEP 2 Number chain. CH3 CH3

CH3─CH─CH─CH3

1 2 3 4

STEP 3 Locate substituents and name.

2,3-dimethylbutane

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Learning Check

Write the name of

Cl CH3

CH3─CH2─CH─CH─CH3

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Solution

STEP 1 Longest chain is pentane.

STEP 2 Number chain from end nearest substituent. Cl CH3

CH3─CH2─CH─CH─CH3

5 4 3 2 1

STEP 3 Locate substituents and name alphabetically.

3-chloro-2-methylpentane

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Learning Check

Give the IUPAC name for each of the following:

A. CH3 CH3

| |

CH3─CH─CH2 ─CH─CH3

B. Cl CH3

| |

CH3─CH2─CH─CH2─C─CH2─CH3

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Cl

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Solution

A. CH3 CH3

| | CH3─CH─CH2 ─CH─CH3 2,4-dimethylpentane 1 2 3 4 5

B. Cl CH3 more substituents = C3 | |

CH3─CH2─CH─CH2─C─CH2─CH3

|

Cl 7 6 5 4 3 2 1

3,5-dichloro-3-methylheptane

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Name the following

The 6 7 8 longest

A. Cl CH2─CH2─CH3 chain | |

CH3─CH2─CH─CH2─C─CH2─CH3

| |

Br Cl 1 2 3 4 5

2-bromo-3,5-dichloro-5-ethyloctane

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Learning Check

Draw the condensed structural formula for

2-bromo-4-chlorobutane.

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Solution

2-bromo-4-chlorobutaneSTEP 1 Longest chain has 4 carbon atoms.

C─C─C─CSTEP 2 Number chain and add substituents.

Br Alphabetically: bromo- first than chloro-

C ─ C ─ C ─ C ─ Cl 1 2 3 4

STEP 3 Add hydrogen to complete 4 bonds to each C.

Br CH3─CH─CH2─CH2─Cl

WRONG name! It is 3-bromo-1-chlorobutane

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Naming Cycloalkanes with Substituents

The name of a substituent is placed in front of the

cycloalkane name.

methylcyclobutane CH3

chlorocyclopentane Cl

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Learning Check

Name each of the following.

1. CH3

CH2─CH3

2.

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Solution

Name each of the following.

1. methylcyclopropane

2. ethylcyclohexane

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Chapter 11 Unsaturated Hydrocarbons

11.1

Alkenes and Alkynes

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Saturated hydrocarbons• have the maximum number of hydrogen atoms

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

CH3—CH2—CH3

cyclohexane

The cycle is considered as one unsaturation

Saturated Hydrocarbons

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Unsaturated hydrocarbons• have fewer hydrogen

atoms attached to the carbon chain than alkanes.

• are alkenes with double bonds.

• are alkynes with triple bonds.

Unsaturated Hydrocarbons

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Bond Angles in Alkenes and Alkynes

According to VSEPR theory: • the three groups bonded to

carbon atoms in a double bond are at 120° angles.

• alkenes are flat because the atoms in a double bond all lie in the same plane.

• the two groups bonded to each carbon in a triple bond are at 180° angles.

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Naming Alkenes

The names of alkenes CnH2n

• use the corresponding alkane name.• change the ending to –ene.

Alkene IUPAC Common

H2C=CH2 ethene ethylene

H2C=CH─CH3 propene propylene

cyclohexene

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Ethene (Ethylene)

Ethene or ethylene• is an alkene with the formula

C2H4. CnH2n

• has two carbon atoms connected by a double bond.

• has two H atoms bonded to each C atom.

• is flat with all the C and H atoms in the same plane.

• is used to accelerate the ripening of fruits.

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Naming Alkynes

The names of alkynes CnH2n-2

• use the corresponding alkane name.• change the ending to –yne.

Alkyne IUPAC Common

HC≡CH ethyne acetylene

HC≡C─CH3 propyne

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Naming Alkenes and Alkynes

When the carbon chain of an alkene or alkyne has four or more C atoms, number the chain to give the lowest number to the first carbon in the 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 2-methyl-2-butene

4. CH3─CC─CH3

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Solution

Write the IUPAC name for each of the following:

1. CH2=CH─CH2─CH3 1-butene

2. CH3─CH=CH─CH3 2-butene

CH3

|3. CH3─CH=C─CH3 2-methyl-2-butene

4. CH3─CC─CH3 2-butyne

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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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Solution

Write the IUPAC name for each of the following:

A. CH3─CH2─C≡C─CH3 2-pentyne

CH3

B. CH3─CH2─C=CH─CH3 3-methyl-2-pentene

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Cis and Trans Isomers

In an alkene the double bond, • is rigid.• holds attached groups in fixed positions. • makes cis/trans isomers possible.

CH3 CH3 CH3 H

C = C C = C

H H H CH3

cis trans

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In cis-trans isomers• there is no rotation around

the double bond in alkenes.• groups attached to the

double bond are fixed relative to each other.

You can make a “double bond” with your fingers with both thumbs on the same side or opposite from each other.

Cis-Trans Isomers

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

attached on the same side of the double bond.

• In the trans isomer, the groups are attached on opposite sides.

Cis-Trans Isomers

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Cis-Trans Isomerism

• Alkenes cannot have cis-trans isomers if a carbon atom in the double bond is attached to identical groups.

Identical Identical

2-bromopropene 1,1-dibromoethene (not cis or trans) (not cis or trans)

C C

H Br

H CH3

C C

H Br

BrH

H

H

H Br

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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.

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Naming Cis-Trans Isomers

The prefixes cis or trans are placed in front of the alkene name when there are cis-trans isomers. cis

cis-1,2-dibromoethene trans-1,2-dibromoethene

C C

Br H

BrH

C C

Br Br

H H

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Learning Check

Name each, using cis-trans prefixes when needed.

C C

CH3 H

CH3H

C C

Br Br

H H

A.

B.

C C

CH3 Cl

ClH

C.

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Solution

cis-1,2-dibromoethene

trans-2-butene

1,1-dichloropropene

C C

CH3 H

CH3H

C C

Br Br

H H

A.

B.

C C

CH3 Cl

ClH

C.

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Alkenes: Compounds with Alkenes: Compounds with C=C Double BondsC=C Double Bonds

How many isomers are possible for a compound How many isomers are possible for a compound with the formula Cwith the formula C44HH88??

CH3

CC

H

CH3H

H

CC

H

CH3H3C

H

CC

H3C

CH3H

2-methylpropene(isobutene)

cis-2-butene trans-2-butene

H

CC

H

CH2CH3H

1-butene

1 2

3 4

1

1

1

2

3

2 23 3

4 4

CH3

CC

H

CH3H

H

CC

H

CH3H3C

H

CC

H3C

CH3H

2-methylpropene(isobutene)

cis-2-butene trans-2-butene

H

CC

H

CH2CH3H

1-butene

1 2

3 4

1

1

1

2

3

2 23 3

4 4