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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
|
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