1 introduction to organic chemistry chapter 11 copyright © the mcgraw-hill companies, inc....
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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
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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
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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
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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
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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•
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Cycloalkanes
Alkanes whose carbon atoms are joined in rings are called cycloalkanes. They have the general formula CnH2n where n = 3,4,…
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Geometry of Cycloalkanes
more stable
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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
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Cis-Trans Isomerization in the Vision Process
electron micrographof retinal rods
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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
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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
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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)
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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
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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
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3
4
5
6
Br
Br
1,2-dibromobenzene
Br
Br
1,3-dibromobenzene
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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
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Polycyclic Aromatic Hydrocarbons
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Functional Group Chemistry
Alcohols contain the hydroxyl functional group and have the general formula R−OH.
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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
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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
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Functional Group Chemistry
Carboxylic acids contain the carboxyl ( −COOH ) functional group.
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• 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
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ChiralityEnantiomers are nonsuperimposable mirror images.
chiral achiral