Chapter 13 Alkanes, Alkynes, and Aromatic Compounds

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Chapter 13 Alkanes, Alkynes, and Aromatic
Compounds
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Saturated Hydrocarbons

• Saturated hydrocarbons
• Have the maximum number of hydrogen atoms
  attached to each carbon atom.
• Are alkanes and cycloalkanes with single C-C
  bonds.
• CH3CH2CH3

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13.1 Alkenes and Alkynes

• Unsaturated hydrocarbons
• Have fewer hydrogen atoms attached to the carbon
  chain than alkanes.
• Are alkenes with double bonds or alkynes with
  triple bonds.

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Alkenes Have Double Bonds

• In a double bond
• One pair of electrons form a strong sigma (?)
  bond.
• One pair of electrons in adjacent p orbitals
  overlap to form a pi (?) bond.

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Alkynes have Triple Bonds

• In a triple bond
• One pair of electrons form a strong sigma (?)
  bond.
• Two pairs of electrons in adjacent p orbitals
  overlap to form two pi (?) bonds.

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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 angles of 120.
• The two groups bonded to each carbon in a triple
  bond are at angles of 180.

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13.2 Naming Alkenes and Alkynes

• In the IUPAC system, the ane ending of the
  corresponding alkane is changed to ene for
  alkenes and to yne for alkynes.

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Naming Alkenes and Alkynes

• When the carbon chain has 4 or more C atoms, the
  chain is numbered to give the lowest number to
  the double or triple bond.
• 1
• CH2CHCH2CH3 1-butene
• 2
• CH3CHCHCH2CH3 2-pentene
• 3
• CH3CH2C?CCH2CH3 3 -hexyne

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Learning Check

• Write the IUPAC name for each
• A. CH3CH2C?CCH3
• CH3
• B. CH3CCHCH3 C.

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Solution

• Write the IUPAC name for each
• A. CH3CH2C?CCH3
• 2-pentyne
• CH3
• B. CH3CCHCH3 C.
• 2-methyl-2-butene
  3-methylcyclopentene

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13.3 The Structure of Alkenes Cis-Trans Isomerism

• 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.

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Cis-Trans Isomers

• Two isomers are possible when groups are attached
  to the double bond.
• 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.

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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-1,2-dibromoethene
  trans-1,2-dibromoethene

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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

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Learning Check

• Name each, using cis-trans prefixes when needed.

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Solution

• cis-1,2-dibromoethene
• trans-2-butene
• 1,1-dichloropropene

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13.4 Properties of Alkenes and Alkynes

• 13.4 Addition Reactions

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Addition Reactions

• The pi (?) bond is easily broken, which makes
  double and triple bonds very reactive.
• In the addition reaction, reactants are added to
  the carbon atoms in the double or triple bond.

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Hydrogenation

• In hydrogenation, hydrogen atoms add to the
  carbon atoms of a double bond or triple bond.
• A catalyst such as Pt or Ni is used to speed up
  the reaction.

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Hydrogenation of Oils

• When hydrogen adds to the double bonds in
  vegetable oils, the products are solids at room
  temperature.

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Learning Check

• Write the equation for the addition of hydrogen
  to 1-butene using a Ni catalyst.

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Solution

• Write the equation for the addition of hydrogen
  to 1-butene using a Ni catalyst.
• Ni
• CH2CHCH2CH3 H2
• CH3CH2CH2CH3

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Halogenation

• In halogenation, halogen atoms add to the carbon
  atoms of a double bond or triple bond.

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Testing for Double and Triple Bonds

• When bromine (Br2) is added to an alkane, the red
  color of bromine persists.
• When bromine (Br2) is added to an alkene or
  alkyne, the red color of bromine disappears
  immediately.

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Learning Check

• Write the product of each addition reaction
• 
  Pt
• CH2CHCH3 H2

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Solution

• Write the product of each addition reaction
• Pt
• CH2CHCH3 H2 CH3CH2CH3

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Hydrohalogenation

• In hydrohalogenation, the atoms of a hydrogen
  halide add to the carbon atoms of a double bond
  or triple bond.

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Markovnikovs Rule

• When an unsymmetrical alkene undergoes
  hydrohalogenation, the H in HX adds to the carbon
  in the double bond that has the greater number of
  H.

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Hydration Adds Water

• In hydration, H and OH from water add to the
  carbon atoms of a double bond or triple bond to
  form alcohols (OH).
• The reaction is catalyzed by acid H.

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Learning Check

• Write the products of each reaction.

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Solution

• Write the products of each reaction.

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13.8 Alkene Polymers
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Polymers

• Polymers are
• Long-chain molecules.
• Found in nature, including cellulose in plants,
  starches in food, proteins and DNA in the body.
• Also synthetic such as polyethylene and
  polystyrene, Teflon, and nylon.

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Common Synthetic Polymers

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Polymerization

• In polymerization, small repeating units called
  monomers are bonded to form a long chain polymer.

Repeating monomer
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Recycling Plastics

• Recycling is simplified by using codes on plastic
  items.
• 1 PETE Polyethyleneterephtalate
• 2 HDPE High-density polyethylene
• 3 PV Polyvinyl chloride
• 4 LDPE Low-density polyethylene
• 5 PP Polypropylene
• 6 PS Polystyrene

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Learning Check

• What is the starting monomer for polyvinyl
  chloride (PVC)?

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Solution

• What is the starting monomer for polyvinyl
  chloride (PVC)?

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Chapter 13 Unsaturated Hydrocarbons

• 13.6 Aromatic Compounds

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13.9 Aromatic Compounds and the Structure of
Benzene

• Benzene is
• An aromatic compound.
• A ring of 6 C atoms and 6 H atoms.
• A flat ring structure drawn with double bonds.
• Represented by two structures because the
  electrons move among the C atoms.

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Benzene Structure

• Because the pi electrons in benzene are shared
  equally among the 6 C atoms, benzene can also be
  represented as a hexagon with a circle drawn
  inside.

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Aromatic Compounds in Nature and Medicine
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13.10 Naming Aromatic Compounds

• A benzene with a single substituent is often
  named as a benzene derivative.
• Methylbenzene Chlorobenzene

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Some Common Names

• Some substituted benzene rings have common names
  that have been in use for many years.

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Naming Aromatic Compounds

• A benzene ring with two or more substituents is
  numbered to give the lowest numbers to the side
  groups.
• Common names use the prefixes ortho- (1,2-),
  meta- (1,3-) and para- (1,4-).

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Learning Check

• Select the correct name for each structure
• 1) chlorocyclohexane
• 2) chlorobenzene
• 3) 1-chlorobenzene
• 1) 1,3-dichlorobenzene
• 2) o-dichlorobenzene
• 3) m-dichlorobenzene

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Solution

• Select the correct name for each structure
• 2) Chlorobenzene
• 1) 1,3-dichlorobenzene
• 3) m-dichlorobenzene

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Learning Check

• Write the structural formula for each
• A. 1-bromo-4-chlorobenzene
• B. o-chlorotoluene

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Solution

• Write the structural formula for each
• A. 1-bromo-4-chlorobenzene
• B. o-chlorotoluene

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Chapter 13 Unsaturated Hydrocarbons

• 13.7 Properties of Aromatic Compounds

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13.11 Reactions of Aromatic Compounds

• Aromatic compounds
• Have a stable aromatic bonding system.
• Are resistant to many reactions.
• Undergo substitution reactions, which retains the
  stability of the aromatic bonding system.

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Substitution Reactions

• In a substitution reaction, a hydrogen atom on a
  benzene ring is replaced by an atom or group of
  atoms.
• Type of substitution H on benzene replaced by
• Halogenation chlorine or bromine atom
• Nitration nitro group (NO2)
• Sulfonation SO3H group

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Halogenation

• Halogenation replaces a H on benzene by a
  chlorine or bromine atom.
• A catalyst such as FeCl3 is used in chlorination
  FeBr3 in bromination.

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Nitration

• Nitration replaces a H on benzene by a nitro
  (NO2) group from HNO3.
• An acid catalyst such as H2SO4 is used in
  nitration.

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Sulfonation

• Sulfonation replaces a H on benzene by a
• SO3H group from SO3.
• An acid catalyst such as H2SO4 is used in
  sulfonation.

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Learning Check

• Write the equation for the bromination of
  benzene, including catalyst.

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Solution

• Write the equation for the bromination of
  benzene, including catalyst.

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Chapter Summary

• Alkenes contain carbon-carbon double bonds.
• Alkynes contain carbon-carbon triple bonds.
• Aromatic compounds contain six carbons in a ring
  arrangement with three double and three single
  bonds alternating between carbon atoms.
• Alkenes are named using the family ending ene,
  while the alkynes use the family ending yne.
• Alkenes and alkynes generally undergo addition
  reactions and aromatic compounds generally
  undergo substitution reactions.
• Reaction mechanism A description of the
  individual steps by which old bonds are broken
  and new bonds are formed.

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• End of Chapter 13

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Thank you

• Thanks so much for a wonderful semester. You have
  been so wonderfully Kind to me.
• I love you so much and will miss you.
• Love
• Divan