1 Chapter 13 Alkanes, Alkynes, and Aromatic Compounds

2 Saturated hydrocarbons:  Have the maximum number of hydrogen atoms attached to each carbon atom.  Are alkanes and cycloalkanes with single C-C bonds. CH 3 —CH 2 —CH 3 Saturated Hydrocarbons

3  Unsaturated hydrocarbons:  Have fewer hydrogen atoms attached to the carbon chain than alkanes.  Are alkenes with double bonds or alkynes with triple bonds Alkenes and Alkynes

4 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.

5 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.

6 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°.

7  In the IUPAC system, the –ane ending of the corresponding alkane is changed to –ene for alkenes and to –yne for alkynes Naming Alkenes and Alkynes

8 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 CH 2 =CH—CH 2 —CH 3 1-butene 2 CH 3 —CH=CH—CH 2 —CH 3 2-pentene 3 CH 3 —CH 2 —C  C—CH 2 —CH 3 3 -hexyne Naming Alkenes and Alkynes

9 Write the IUPAC name for each: A. CH 3 —CH 2 —C  C—CH 3 CH 3 | B. CH 3 —C=CH—CH 3 C. Learning Check

10 Write the IUPAC name for each: A. CH 3 — CH 2 — C  C — CH 3 2-pentyne CH 3 | B. CH 3 —C=CH—CH 3 C. 2-methyl-2-butene 3-methylcyclopentene Solution

11  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 The Structure of Alkenes: Cis-Trans Isomerism

12  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. Cis-Trans Isomers

13 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.

14 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

15 Cis-Trans Isomerism Alkenes cannot have cis-trans isomers if a carbon atom in the double bond is attached to identical groups. Identical 2-bromopropene 1,1-dibromoethene

16 Learning Check Name each, using cis-trans prefixes when needed.

17 Solution cis-1,2-dibromoethene trans-2-butene 1,1-dichloropropene

Addition Reactions 13.4 Properties of Alkenes and Alkynes

19 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.

20  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. Hydrogenation

21  When hydrogen adds to the double bonds in vegetable oils, the products are solids at room temperature. Hydrogenation of Oils

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

23 Write the equation for the addition of hydrogen to 1-butene using a Ni catalyst. Ni CH 2 =CH—CH 2 —CH 3 + H 2 CH 3 —CH 2 —CH 2 —CH 3 Solution

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

25 Testing for Double and Triple Bonds When bromine (Br 2 ) is added to an alkane, the red color of bromine persists. When bromine (Br 2 ) is added to an alkene or alkyne, the red color of bromine disappears immediately.

26 Write the product of each addition reaction: Pt CH 2 =CH—CH 3 + H 2 Learning Check

27 Write the product of each addition reaction: Pt CH 2 =CH—CH 3 + H 2 CH 3 —CH 2 —CH 3 Solution

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

29 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. Markovnikov’s Rule

30 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 +. Hydration Adds Water

31 Learning Check Write the products of each reaction.

32 Solution Write the products of each reaction.

Alkene Polymers

34 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.

35 Common Synthetic Polymers

36 Polymerization In polymerization, small repeating units called monomers are bonded to form a long chain polymer. Repeating monomer

37

38 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

39 Learning Check What is the starting monomer for polyvinyl chloride (PVC)?

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

41 Chapter 13 Unsaturated Hydrocarbons 13.6 Aromatic Compounds

42  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 Aromatic Compounds and the Structure of Benzene

43  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. Benzene Structure

44 Aromatic Compounds in Nature and Medicine

45 A benzene with a single substituent is often named as a benzene derivative. Methylbenzene Chlorobenzene Naming Aromatic Compounds

46 Some substituted benzene rings have common names that have been in use for many years. Some Common Names

47 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-). Naming Aromatic Compounds

48 Select the correct name for each structure: 1) chlorocyclohexane 2) chlorobenzene 3) 1-chlorobenzene 1) 1,3-dichlorobenzene 2) o-dichlorobenzene 3) m-dichlorobenzene Learning Check

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

50 Write the structural formula for each: A. 1-bromo-4-chlorobenzene B. o-chlorotoluene Learning Check

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

52 Chapter 13 Unsaturated Hydrocarbons 13.7 Properties of Aromatic Compounds

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.

54 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 (—NO 2 ) Sulfonation —SO 3 H group

55 Halogenation Halogenation replaces a H on benzene by a chlorine or bromine atom. A catalyst such as FeCl 3 is used in chlorination; FeBr 3 in bromination.

56 Nitration Nitration replaces a H on benzene by a nitro (—NO 2 ) group from HNO 3. An acid catalyst such as H 2 SO 4 is used in nitration.

57 Sulfonation Sulfonation replaces a H on benzene by a —SO 3 H group from SO 3. An acid catalyst such as H 2 SO 4 is used in sulfonation.

58 Learning Check Write the equation for the bromination of benzene, including catalyst.

59 Solution Write the equation for the bromination of benzene, including catalyst.

60 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.

61 End of Chapter 13

62 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