Introductory Chemistry: Concepts & Connections

4 th Edition by Charles H. Corwin

Chapter 19

Organic Chemistry

Christopher G. Hamaker, Illinois State University, Normal IL © 2005, Prentice Hall

Introduction

•

Organic chemistry

compounds.

is the study of carbon and its • The major sources of carbon are the fossil fuels: petroleum, natural gas, and coal.

• Currently, about 7 million organic compounds account for about 90% of all known substances.

• Each year, over 50,000 new organic compounds are synthesized.

Chapter 19 2

Conclusions Continued

• A

hydrocarbon

is a compound that contains

only

carbon and hydrogen.

• A

hydrocarbon derivative

is a compound derived from a hydrocarbon but containing other elements such a fluorine, nitrogen, and oxygen.

• There are two types of hydrocarbons: – Saturated hydrocarbons – Unsaturated hydrocarbons Chapter 19 3

Saturated Hydrocarbons

• A

saturated hydrocarbon

between the carbon atoms.

has only single bonds • Carbon can form four single covalent bonds to other atoms.

• A saturated hydrocarbon with only single bonds belongs to the

alkane

family.

Chapter 19 4

Unsaturated Hydrocarbons

• An

unsaturated hydrocarbon

has either a double or triple bond between two carbon atoms.

– If it has a double bond, it is an

alkene

(b).

– If it has a triple bond, it is an

alkyne

(c).

• An

aromatic hydrocarbon

has a benzene ring. A benzene ring is a 6-membered ring of carbon atoms with alternating single and double bonds (d) .

Chapter 19 5

Classification of Hydrocarbons

• Below is a flowchart for the classification of hydrocarbons.

Chapter 19 6

Alkanes

• Alkanes are a family of compounds whose names end in the suffix

-ane

. They are saturated hydrocarbons.

• They each have the same general molecular formula: C

n

H

2n+2

.

– The fifth member of the alkane family, pentane, has 5 carbon atoms and (2 × 5 + 2 = 12) hydrogen atoms, C 5 H 12 .

Chapter 19 7

Alkane Family

• The lighter alkanes (1 – 10 carbons) are used as fuels while the larger alkanes (20 – 40 carbons) are solids used to make waxes and candles.

Chapter 19 8

Structural Isomers

• Two compounds with the same molecular formula but different structural formulas are

isomers

.

• Butane has the formula C 4 H 10 . We can draw the formula in two ways: CH 3 CH 2 CH 2 CH 3 and CH 3 CH(CH 3 )CH 3 • The two isomers have different physical properties.

Chapter 19 9

Alkyl and Aryl Groups

• When a hydrogen is removed from an alkane, an

alkyl group

results.

CH 4 - H = CH 3 – methane methyl group CH 3 -CH 3 ethane - H = CH 3 -CH 2 – ethyl group • When we remove the hydrogen atom, the name

-ane

suffix is changed to

-yl

.

Chapter 19 10

Alkyl and Aryl Groups

Chapter 19 11

Guidelines for Naming Alkanes

1. Name an alkane for its longest continuous carbon chain regardless of the branches.

2. Number the longest continuous chain starting from the end closest to the first branch on the chain.

3. Indicate the position of the alkyl groups by name and number.

4. If there are two or more of the same group attached to the chain, use the prefixes

di-

,

tri-

,

tetra-

, etc.

Chapter 19 12

Nomenclature of Alkanes

• What is the name of the following alkane?

CH 3 C H 3 6 C H 3 5 C H 2 4 C H 2 3 C H 2 C H 3 1 • The longest chain has 6 carbons, so it is a

hexane

derivative. The methyl group is in the 2 position. • The name is 2-methylhexane.

Chapter 19 13

Nomenclature of Alkanes

• What is the name of the following alkane?

5 4 3 2 1 • The longest chain has 5 carbons, so it is a

pentane

derivative. The methyl groups are in the 2 and 3 positions. • The name is 2,3-dimethylpentane.

Chapter 19 14

Alkane Reactions

• The C-C and C-H bonds in alkanes are very strong and unreactive at room temperature.

• At high temperatures, alkanes burn rapidly in the presence of oxygen. This is a

combustion reaction

.

spark CH 4 (g) + 2 O 2 (g) → CO 2 (g) + 2 H 2 O(g) • The products of a combustion reaction are carbon dioxide and water.

Chapter 19 15

Alkene & Alkyne Formulas

• Alkenes contain one or more double bonds. The general molecular formula for an alkene with one double bond is C

n

H

2n

.

– The fifth member of the alkene family, pentene, has 5 carbon atoms and (2 × 5 = 10) hydrogen atoms, C 5 H 10 .

• Alkynes contain one or more triple bonds. The general molecular formula for an alkyne with one triple bond is C

n

H

2n-2

.

– The fifth member of the alkyne family, pentyne, has 5 carbon atoms and (2 × 5 – 2 = 8) hydrogen atoms, C 5 H 8 .

Chapter 19 16

Alkene Family

• Butene, C 4 H 8 , has two structural isomers. The double bond can be between the first and second carbon or between the second and third carbon.

Chapter 19 17

Guidelines for Naming Alkenes

1. Name an alkene for its

longest

chain that

contains

continuous carbon the double bond. The name is the same as the alkane with the

-ane

changed to

-ene

.

suffix 2. Number the longest continuous chain starting from the end closest to the double bond.

3. Indicate the position of the attached alkyl groups by name and number.

4. If there are two or more of the same group attached to the chain, use the prefixes

di-

,

tri-

,

tetra-

, etc.

Chapter 19 18

Nomenclature of Alkenes

• What is the name of the following alkene?

5 4 3 2 1 • The longest chain with the double bond has 5 carbons, so it is a

pentene

derivative. The double bond is the first bond, so it is a

1-pentene

. The ethyl group is in the 2 position. • The name is 2-ethyl-1-pentene.

Chapter 19 19

Alkyne Family

• Butyne, C 4 H 6 , has two structural isomers. The triple bond can be between the first and second carbon or between the second and third carbon.

Chapter 19 20

Guidelines for Naming Alkynes

1. Name an alkene for its

longest

chain that

contains

continuous carbon the triple bond. The name is the same as the alkane with the changed to

-yne

.

-ane

suffix 2. Number the longest continuous chain starting from the end closest to the triple bond.

3. Indicate the position of the attached alkyl groups by name and number.

4. If there are two or more of the same group attached to the chain, use the prefixes

di-

,

tri-

,

tetra-

, etc.

Chapter 19 21

Nomenclature of Alkynes

• What is the name of the following alkyne?

1 2 3 4 • The longest chain with the triple bond has 4 carbons, so it is a

butyne

derivative. The triple bond is the first bond, so it is a

1-butyne

. The methyl group is in the 3 position. • The name is 3-methyl-1-butyne.

Chapter 19 22

Reactions of Alkenes & Alkynes

• In addition to combustion reactions, alkenes and alkynes also undergo

addition reactions

. The double or triple bond can add atoms. There are two types: hydrogenation and halogenation.

• Hydrogenation Ni – CH≡CH(g) + H 2 (g) → CH 2 =CH 2 (g) • Halogenation – CH 2 =CH 2 (l) + Br 2 (l) → CH 2 Br-CH 2 Br(l) Chapter 19 23

Polymerization Reactions

• A polymer is a giant molecule made up from many small molecules (monomers) joined in a long chain.

• Ethylene, CH 2 =CH 2 , can react to give

polyethlyene

.

• We represent the polymer as [-CH 2 -CH 2 -]

n

.

n

CH 2 =CH 2 → [-CH 2 -CH 2 -]

n monomer polymer

Chapter 19 24

Arenes

•

Arenes

contain a

benzene

ring.

• Arenes are also called

aromatic

because of their fragrant smell.

compounds • The formula for benzene is C 6 H 6 cyclic structure.

and it has a • The double bonds are

delocalized

and benzene is often written with a circle in the middle.

Chapter 19 25

Isomers of Disubstituted Benzene

• If we replace two of the hydrogens on benzene with chlorines, we have dichlorobenzene, C 6 H 4 Cl 2 .

• The chlorine atoms can be arranged in three different ways: Chapter 19 26

Isomers of Disubstituted Benzene

• If the chlorines are on adjacent carbons, we have

ortho

-dichlorobenzene.

• If the chlorines are separated by one carbon, we have

meta

-dichlorobenzene.

• If the chlorines are opposite each other, we have

para

dichlorobenzene.

Chapter 19 27

Hydrocarbon Derivatives

• There are millions of organic compounds.

• We can categorize them into

classes of compounds

.

• Each of the classes has a specific

functional group

. A function group is a set of atoms that gives a class of compounds its characteristics.

• There are 10 classes: five without a

carbonyl

group and five with a carbonyl group (C=O).

Chapter 19 28

Non-Carbonyl Classes of Hydrocarbon Derivatives

• Here are the basic hydrocarbon classes. R is an alkyl group and Ar is an aryl group.

Chapter 19 29

Carbonyl Classes of Hydrocarbon Derivatives

Chapter 19 30

Organic Halides

• If a halogen atom (F, Cl, Br, I) replaces a hydrogen atom in a hydrocarbon, the new compound is an

organic halide

.

• Organic halides are used primarily as household and industrial solvents.

• They are found in many pesticides.

• They are essentially nonpolar molecules with low boiling points and properties similar to those of alkanes.

Chapter 19 31

Alcohols & Phenols

• When an –OH group replaces a hydrogen atom on an alkane, the result is an

alcohol

.

• When an –OH replaces a hydrogen atom on a arene, the resulting molecule is a

phenol

.

• The –OH group is called a

hydroxyl group

.

• The name of alcohols is derived from the parent alkane by changing the

-ane

ending to a

-ol

suffix.

– For example, CH 3 CH 2 OH is ethanol Chapter 19 32

Alcohols & Phenol Continued

• Most alcohols are quite water soluble because of the polar –OH group which allows for hydrogen bonding.

• Alcohols higher boiling points are different than their parent alkanes.

Chapter 19 33

Ethers

• Organic molecules with two hydrocarbon groups attached to an oxygen are

ethers

, R-O-R.

• Ethers are usually named by indicating the two groups attached to the oxygen.

• Ethers do not hydrogen bond and their properties lie between those of alkanes and alcohols.

Chapter 19 34

Amines

• If an alkyl or aryl group replaces a hydrogen in ammonia, an

amine

results, R-NH 2 .

• Amines are often referred to by their common names, indicating the alkyl group present.

• Most amines are polar due to their ability to hydrogen bond.

Chapter 19 35

Aldehydes

•

Aldehydes

polar.

contain a carbonyl (C=O) group and are • In an aldehyde, the carbonyl group is attached to a hydrogen and an alkyl or aryl group, RCHO.

• The name of an aldehyde is derived from its parent alkane by changing the

-ane

to an

-al

suffix.

Chapter 19 36

Ketones

•

Ketones

also contain the carbonyl group and are generally polar.

• Ketones have two alkyl or aryl groups attached to the carbonyl group.

• Ketones are named for their parent alkane.

Chapter 19 37

Carboxylic Acids

• In a

carboxylic acid

, a hydroxyl group and alkyl or aryl group is bonded to a carbonyl group, RCOOH.

• This group, -COOH, is a

carboxyl group

.

• Acetic acid, CH 3 COOH, is a major component of vinegar and gives it its sour taste.

• Carboxylic acids are named from their parent alkane by dropping the

-ane

ending and replacing it with a

-oic acid

suffix.

Chapter 19 38

Carboxylic Acids Continued

• Carboxylic acids are polar since the carboxyl group, –COOH, can form hydrogen bonds.

• They have similar properties to alcohols with high boiling points and good water solubility.

Chapter 19 39

Esters

• An

ester

has an –R and an –OR group bonded to a carbonyl group, RCOOR. • Esters typically have a pleasant, fruity odor.

• They are slightly polar.

• They are typically formed from the reaction of an alcohol with a carboxylic acid.

Chapter 19 40

Amides

• In

amides

, a carbonyl group is attached to an alkyl or aryl group and an –NH 2 group.

• Amides are formed from the reaction of a carboxylic acid with ammonia.

• They are polar molecules with properties similar to those of carboxylic acids.

Chapter 19 41

Conclusions

• Organic chemistry is the study of compounds that contain carbon.

• Hydrocarbons contain only hydrogen and carbon.

• Saturated hydrocarbons have only single carbon carbon bonds.

• Unsaturated hydrocarbons have double or triple carbon-carbon bonds.

• Aromatic hydrocarbons have a benzene ring.

Chapter 19 42

Conclusions Continued

• Alkenes have at least one carbon-carbon double bond.

• Alkynes have at least one carbon-carbon triple bonds.

• Arenes contain a benzene ring.

• Hydrocarbon derivatives have a functional group in addition to the hydrocarbon function. They are summarized on the next slide.

Chapter 19 43

Chapter 19 44