Introduction to Organic
Chemistry
Chapter 11
1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Common Elements in Organic Compounds
2
Classification of Hydrocarbons
Hydrocarbons are made up of only hydrogen and carbon.
3
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
4
Structural isomers are molecules that have the same
5
molecular formula but different structures
How many structural isomers does pentane, C5H12, have?
H
H
H
H
H
H
C
C
C
C
C
H
H
H
H
H
H
H
CH3 H
C
C
H
CH3 H
n-pentane
H
H
H
CH3 H
H
C
C
C
C
H
H
H
H
2-methylbutane
H
C
H
2,2-dimethylpropane
6
Physical Properties of Some Alkanes
7
Alkane Nomenclature
1. The parent name of the hydrocarbon is that given to the
longest continuous chain of carbon atoms in the molecule.
CH3
CH3
1
CH2
2
CH2
3
CH
4
4-methylheptane
CH2
5
CH2
6
CH3 heptane
7
2. An alkane less one hydrogen
atom is an alkyl group.
CH4
methane
CH3
methyl
8
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
CH3
1
CH
2
CH2
3
CH2
4
CH3
5
CH3
2-methylpentane
CH3
1
CH2
2
CH2
3
CH
CH3
4
4-methylpentane
5
9
Alkane Nomenclature
4. Use prefixes di-, tri-, tetra-, when there is more than one
alkyl branch of the same kind.
CH3
1
CH3
CH3
CH
CH
2
3
CH2
CH2
4
CH3
5
6
2,3-dimethylhexane
CH3
CH3
1
CH
2
C
3
CH2
4
CH2
5
CH3
6
CH3
3,3-dimethylhexane
10
Alkane Nomenclature
5. Use previous rules for other types of substituents.
CH3
1
Br
NO2
CH
CH
2
3
CH3
4
2-bromo-3-nitrobutane
Cl
CH2
1
F
CH2
2
CH
3
CH3
4
1-chloro-3-fluorobutane
11
What is the IUPAC name of the following compound?
CH3
CH3
1
CH
C2H5
CH2
2
3
CH
4
CH2
5
CH2
6
CH2
7
CH3
8
2-methyl-4-ethyloctane
What is the structure of 4-ethyl-2-methylhexane?
CH3
CH3
1
CH
2
C2H5
CH2
3
CH
4
CH2
5
CH3
6
12
Alkane Reactions
Combustion
CH4 (g) + 2O2 (g)
CO2 (g) + 2H2O (l) DH0 = -890.4 kJ/mol
Halogenation
light
CH4 (g) + Cl2 (g)
CH3Cl (g) + HCl (g)
Cl2 + energy
Cl• + Cl•
H
H
Cl• + H
C
H
H
•C
H
H
H
C • + Cl
H + HCl
H
Cl
H
C
Cl + Cl•
13
H
H
Cycloalkanes
Alkanes whose carbon atoms are joined in rings are called
cycloalkanes. They have the general formula CnH2n where n =
3,4,…
14
Geometry of Cycloalkanes
more stable
15
Alkenes
Alkenes have the general formula CnH2n where n = 2,3,…
• contain at least one carbon-carbon double bond
• also called olefins
CH
CH2
CH2
CH3
CH3
CH
1-butene
Cl
Cl
C
H
Cl
H
C
cis-dichloroethylene
CH3
2-butene
C
H
CH
H
C
Cl
trans-dichloroethylene
16
Cis-Trans Isomerization in the Vision Process
electron micrograph
of retinal rods
17
Alkene Reactions
Cracking
C2H6 (g)
Pt
catalyst
CH2
CH2 (g) + H2 (g)
Addition Reactions
CH2
CH2 (g) + HBr (g)
CH3
CH2
CH2 (g) + Br2 (g)
CH2Br
CH2Br (g)
CH2Br (g)
18
and/or
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.
19
Alkynes
Alkynes have the general formula CnH2n-2 where n = 2,3,4,…
• contain at least one carbon-carbon triple bond
CH
C
CH2
1-butyne
CH3
CH3
C
C
CH3
2-butyne
Production of acetylene
CaC2 (s) + 2H2O (l)
C2H2 (g) + Ca(OH)2 (aq)
20
Alkyne Reactions
Hydrogenation
CH
CH (g) + H2 (g)
CH2
CH2 (g)
Addition Reactions
CH
CH (g) + HBr (g)
CH2
CH
CH (g) + Br2 (g)
CHBr
CH
CH (g) + 2Br2 (g)
CHBr2
CHBr (g)
CHBr (g)
CHBr2 (g)
21
Aromatic Hydrocarbons
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
C
C
C
C
C
C
H
H
H
Electron micrograph
of benzene
22
Delocalized molecular orbitals are not confined between
two adjacent bonding atoms, but actually extend over three
or more atoms.
Example: Benzene, C6H6
Delocalized p orbitals
23
Other Representations of Benzene
24
Aromatic Compound Nomenclature
ethylbenzene
CH2CH3
aminobenzene
NH2
Cl
chlorobenzene
6
2
5
3
4
nitrobenzene
Br
Br
1
NO2
Br
Br
1,2-dibromobenzene
1,3-dibromobenzene
25
Aromatic Compound Reactions
Substitution reaction
H
Br
H
H
+ Br2
H
H
H
FeBr3
catalyst
+ HBr
H
H
H
H
H
H
CH2CH3
H
H
+ CH3CH2Cl
H
H
H
H
H
AlCl3
catalyst
+ HCl
H
H
H
26
Polycyclic Aromatic Hydrocarbons
27
Functional Group Chemistry
Alcohols contain the hydroxyl functional group and have the
general formula R−OH.
28
Biological production of ethanol
C6H12O6 (aq)
enzyme
2CH3CH2OH (aq) + 2CO2 (g)
Commercial production of ethanol
CH2 CH2 (g) + H2O (g)
H2SO4
CH3CH2OH (g)
Metabolic oxidation of ethanol
CH3CH2OH
alcohol dehydrogenase
CH3CHO + H2
29
Functional Group Chemistry
Ethers have the general formula R−O−R′.
Condensation Reaction
CH3OH + HOCH3
H2SO4
catalyst
CH3OCH3 + H2O
30
Functional Group Chemistry
O
Aldehydes and ketones contain the carbonyl ( C
functional group.
O
)
• aldehydes have the general formula R C H
O
• ketones have the general formula R C R′
O
O
O
H C H
H C CH3
H3C C CH3
formaldehyde
acetaldehyde
acetone
31
Functional Group Chemistry
Carboxylic acids contain the carboxyl ( −COOH ) functional
group.
32
Properties and Reactions of Carboxylic Acids
• Generally weak acids
• React with alcohols to form esters
• Neutralization
• Production of acid halides (intermediates in syntheses)
33
Functional Group Chemistry
Esters have the general formula R′COOR, where R is a
hydrocarbon group.
Characteristic odors and flavors
Hydrolysis
Alkaline hydrolysis (saponification)
34
Functional Group Chemistry
Amines are organic bases with the general formula R3N.
CH3NH2 + H2O
RNH3+ + OH-
Neutralization
CH3CH2NH2 + HCl
CH3CH2NH3+Cl-
35
Chirality
Enantiomers are nonsuperimposable mirror images.
chiral
achiral
36