1 Introduction to Organic Chemistry Chapter 11 Copyright © The McGraw-Hill Companies, Inc....

1

Introduction to Organic Chemistry

Chapter 11

Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.

2

Common Elements in Organic Compounds

3

Classification of Hydrocarbons

Hydrocarbons are made up of only hydrogen and carbon.

4

Alkanes

Alkanes have the general formula CnH2n+2 where n = 1,2,3,…

• only single covalent bonds

• saturated hydrocarbons because they contain the maximum number of hydrogen atoms that can bond with the number of carbon atoms in the molecule

CH4 C2H6 C3H8

methane ethane propane

5

Structural isomers are molecules that have the same molecular formula but different structures

6

How many structural isomers does pentane, C5H12, have?

C C C C C

H H H H H

H

HHHHH

H

C C C C

H CH3 H H

H

HHHH

H

C C C

H CH3 H

H

HH

H

CH3

n-pentane

2-methylbutane

2,2-dimethylpropane

7

Physical Properties of Some Alkanes

8

Alkane Nomenclature

1. The parent name of the hydrocarbon is that given to the longest continuous chain of carbon atoms in the molecule.

CH3 CH2 CH2 CH CH2 CH2 CH3

CH3

1 2 3 4 5 6 7heptane

2. An alkane less one hydrogen atom is an alkyl group.

CH4

CH3

methane

methyl

4-methylheptane

9

Alkane Nomenclature

3. When one or more hydrogen atoms are replaced by other groups, the name of the compound must indicate the locations of carbon atoms where replacements are made. Number in the direction that gives the smaller numbers for the locations of the branches.

CH3 CH CH2 CH2 CH3

CH3

1 2 3 4 5

2-methylpentane

CH3 CH2 CH2 CH CH3

CH3

1 2 3 4 5

4-methylpentane

10

Alkane Nomenclature

4. Use prefixes di-, tri-, tetra-, when there is more than one alkyl branch of the same kind.

CH3 CH CH CH2 CH2 CH3

CH3

1 2 3 4 5 6

CH3

2,3-dimethylhexane

CH3 CH C CH2 CH2 CH3

CH3

1 2 3 4 5 6

CH3

3,3-dimethylhexane

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Alkane Nomenclature

5. Use previous rules for other types of substituents.

CH3 CH CH CH3

Br

1 2 3 4

NO2

2-bromo-3-nitrobutane

CH2 CH2 CH CH3

Cl

1 2 3 4

F

1-chloro-3-fluorobutane

12

What is the IUPAC name of the following compound?

1 2 3 4 5 6 7 8CH3 CH CH2 CH CH2 CH2 CH3

C2H5

CH2

CH3

2-methyl-4-ethyloctane

What is the structure of 4-ethyl-2-methylhexane?

1 2 3 4 5 6CH3 CH CH2 CH CH2 CH3

C2H5CH3

13

Alkane Reactions

CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l) H0 = -890.4 kJ/mol

Combustion

Halogenation

CH4 (g) + Cl2 (g) CH3Cl (g) + HCl (g)light

Cl2 + energy Cl• + Cl•

Cl• + C HH

H

H

C H

H

H

• + HCl

CH

H

H

• + Cl Cl C ClH

H

H

+ Cl•

14

Cycloalkanes

Alkanes whose carbon atoms are joined in rings are called cycloalkanes. They have the general formula CnH2n where n = 3,4,…

15

Geometry of Cycloalkanes

more stable

16

Alkenes

Alkenes have the general formula CnH2n where n = 2,3,…

• contain at least one carbon-carbon double bond

• also called olefins

CH2 CH CH2 CH3

1-butene

CH3 CH CH CH3

2-butene

C C

Cl Cl

H H

C C

Cl H

H Cl

cis-dichloroethylene trans-dichloroethylene

17

Cis-Trans Isomerization in the Vision Process

electron micrographof retinal rods

18

Alkene ReactionsCracking

Addition Reactions

CH2 CH2 (g) + HBr (g) CH3 CH2Br (g)

CH2 CH2 (g) + Br2 (g) CH2Br CH2Br (g)

C2H6 (g) CH2 CH2 (g) + H2 (g)Pt

catalyst

19

Markovnikov’s rule: in the addition of unsymmetrical (that is, polar) reagents to alkenes, the positive portion of the reagent (usually hydrogen) adds to the carbon atom that already has the most hydrogen atoms.

and/or

20

Alkynes

Alkynes have the general formula CnH2n-2 where n = 2,3,4,…

• contain at least one carbon-carbon triple bond

1-butyne 2-butyne

CH C CH2 CH3 CH3 C C CH3

Production of acetylene

CaC2 (s) + 2H2O (l) C2H2 (g) + Ca(OH)2 (aq)

21

Alkyne Reactions

Addition Reactions

Hydrogenation

CH CH (g) + H2 (g) CH2 CH2 (g)

CH CH (g) + HBr (g) CH2 CHBr (g)

CH CH (g) + Br2 (g) CHBr CHBr (g)

CH CH (g) + 2Br2 (g) CHBr2 CHBr2 (g)

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Aromatic Hydrocarbons

C

CC

CC

C

H

H

H

H

H

H

C

CC

CC

C

H

H

H

H

H

H

Electron micrographof benzene

23

Delocalized molecular orbitals are not confined between two adjacent bonding atoms, but actually extend over three or more atoms.

Example: Benzene, C6H6

Delocalized orbitals

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Other Representations of Benzene

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Aromatic Compound Nomenclature

CH2CH3

ethylbenzene

Cl

chlorobenzene

NH2

aminobenzene

NO2

nitrobenzene

12

3

4

5

6

Br

Br

1,2-dibromobenzene

Br

Br

1,3-dibromobenzene

26

Aromatic Compound Reactions

H

H

H

H

H

H

Br

H

H

H

H

H

+ HBr+ Br2

FeBr3

catalyst

H

H

H

H

H

H

CH2CH3

H

H

H

H

H

+ HCl+ CH3CH2ClAlCl3

catalyst

Substitution reaction

27

Polycyclic Aromatic Hydrocarbons

28

Functional Group Chemistry

Alcohols contain the hydroxyl functional group and have the general formula R−OH.

29

C6H12O6 (aq) 2CH3CH2OH (aq) + 2CO2 (g)enzyme

CH2 CH2 (g) + H2O (g) CH3CH2OH (g)H2SO4

Biological production of ethanol

Commercial production of ethanol

Metabolic oxidation of ethanol

CH3CH2OH CH3CHO + H2

alcohol dehydrogenase

30

Functional Group Chemistry

Ethers have the general formula R−O−R′.

CH3OH + HOCH3 CH3OCH3 + H2OH2SO4

catalyst

Condensation Reaction

31

Functional Group Chemistry

Aldehydes and ketones contain the carbonyl ( ) functional group.

O

C

R C H

O

• aldehydes have the general formula

R C R′

O

• ketones have the general formula

H C H

O

H C

O

CH3 C

O

CH3H3C

formaldehyde acetaldehyde acetone

32

Functional Group Chemistry

Carboxylic acids contain the carboxyl ( −COOH ) functional group.

33

• Generally weak acids• React with alcohols to form esters

• Neutralization

• Production of acid halides (intermediates in syntheses)

Properties and Reactions of Carboxylic Acids

34

Functional Group Chemistry

Esters have the general formula R′COOR, where R is a hydrocarbon group.

Hydrolysis

Alkaline hydrolysis (saponification)

Characteristic odors and flavors

35

Functional Group Chemistry

Amines are organic bases with the general formula R3N.

CH3NH2 + H2O RNH3+ + OH-

CH3CH2NH2 + HCl CH3CH2NH3+Cl-

Neutralization

36

ChiralityEnantiomers are nonsuperimposable mirror images.

chiral achiral