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Chapter 11 Unsaturated Hydrocarbons

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1 Chapter 11 Unsaturated Hydrocarbons
11.1 Alkenes and Alkynes

2 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

3 Unsaturated Hydrocarbons
have fewer hydrogen atoms attached to the carbon chain than alkanes. are alkenes with double bonds. are alkynes with triple bonds.

4 Naming Alkenes The names of alkenes use the corresponding alkane name.
change the ending to –ene. Alkene IUPAC Common H2C=CH2 ethene ethylene H2C=CH─CH3 propene propylene cyclohexene

5 Ethene (Ethylene) Ethene, or ethylene,
is an alkene with the formula C2H4. 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. Copyright © by Pearson Education, Inc.

6 Naming Alkynes The names of alkynes use the corresponding alkane name.
change the ending to –yne. Alkyne IUPAC Common HC≡CH ethyne acetylene HC≡C─CH3 propyne

7 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 CH3─CH=CH─CH3 2-butene CH3─CH2─CC─CH3 2-pentyne

8 Guide to Naming Alkenes and Alkynes

9 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 4. CH3─CC─CH3

10 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─CC─CH3 2-butyne

11 Learning Check Write the IUPAC name for each of the following:
A. CH3─CH2─C≡C─CH3 CH3 B. CH3─CH2─C=CH─CH3

12 Solution Write the IUPAC name for each of the following:
A. CH3─CH2─C≡C─CH pentyne CH3 B. CH3─CH2─C=CH─CH3 3-methyl-2-pentene

13 Name this compound: Longest chain containing C=C is 5 carbons
ethyl 5 3 4 2 1 Longest chain containing C=C is 5 carbons 2-ethyl-1-pentene

14 Fragrant Alkenes

15 Chapter 11 Unsaturated Hydrocarbons
11.2 Cis-Trans Isomers 15

16 Cis and Trans Isomers In an alkene, the double bond is rigid.
holds attached groups in fixed positions. makes cis-trans isomers possible. cis-2-butene trans-2-butene 16

17 Trans is a Latin noun or prefix, meaning “across”, “beyond” or “on the opposite side”.
Cis is a Latin prefix, meaning “on the same side [as]” , “on this side [of]”, or “near side [of]”. 17

18 Cis-Trans Isomers 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. 18

19 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-Dibromoethene (not cis or trans) (not cis or trans) H Br H H 19

20 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. 20

21 Naming Cis-Trans Isomers
The prefix of cis or trans is placed in front of the alkene name when the compound is a cis or trans isomer. cis trans cis-1,2-Dibromoethene trans-1,2-Dibromoethene 21

22 Learning Check Name each, using cis-trans prefixes when needed. 22

23 Solution cis-1,2-Dibromoethene trans-2-Butene 1,1-Dichloropropene 23

24 Chapter 11 Unsaturated Hydrocarbons
11.3 Addition Reactions 24

25 Addition Reactions In alkene and alkynes,
the double or triple bond is easily broken, which makes double and triple bonds very reactive. in addition reactions, reactants are added to the carbon atoms in the double or triple bond. 25

26 Addition of X2 Halogenation In halogenation,
halogen atoms such as chlorine or bromine are added to the carbon atoms of a double bond. the reaction occurs rapidly, without the use of a catalyst.

27 Addition of X2 Halogenation Examples

28 Addition of X2 The addition reaction of bromine
is used to test for the presence of double bonds. When bromine is added to an alkane in the first test tube, the orange color of bromine remains because the alkane does not react. When bromine is added to an alkene in the second test tube, the orange color quickly disappears as bromine atoms add to the double bond to give colorless products.

29 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. 29

30 Hydrogenation of Oils Adding H2 to double bonds in vegetable
oils produces compounds with higher melting points. solids at room temperature, such as margarine, soft margarine, and shortening. 30

31 Reaction Example Write an equation for the hydrogenation of 1-butene using a platinum catalyst. Pt CH2=CH─CH2─CH3 + H CH3─CH2─CH2─CH3 31

32 Trans Fats In vegetable oils, the unsaturated fats usually contain
cis double bonds. During hydrogenation, some cis double bonds are converted to trans double bonds (more stable), causing a change in the fatty acid structure. If a label states “partially” or “fully hydrogenated,” the fats contain trans fatty acids. 32

33 Learning Check Write the product of each the following: Pt
CH3─CH=CH─CH3 + H2 + H2 33

34 Solution Pt 1. CH3─CH=CH─CH3 + H CH3─CH2─CH2─CH3 H2 34

35 Hydration In the addition reaction called hydration,
an acid H+ catalyst is required. water (HOH) adds to a double bond. an H atom bonds to one C in the double bond. an OH bonds to the other C. H OH H │ │ CH3─CH=CH─CH3 + H─OH CH3─CH─CH─CH3 35

36 Hydration When hydration occurs with a double bond that has an
unequal number of H atoms, the H atom bonds to the C in the double bond with the more H. the OH bonds to the C in the double bond with the fewer H atoms. OH H H │ │ CH3─CH=CH2 + H─OH CH3─CH─CH2 C has 1 H C has 2 H’s Them that has, gets! 36

37 Learning Check Write the product for the hydration of each of the
following: H+ 1. CH3─CH2─CH=CH─CH2─CH HOH CH3 │ H+ 2. CH3─C=CH─CH2─CH HOH HOH 37

38 Solution H OH │ │ 1. CH3─CH2─CH─CH─CH2─CH3 CH3 │ 2. CH3─C─CH─CH2─CH3
│ │ 1. CH3─CH2─CH─CH─CH2─CH3 CH3 2. CH3─C─CH─CH2─CH3 │ │ OH H OH 3. H 38

39 Chapter 11 Unsaturated Hydrocarbons
11.4 Polymers of Alkenes 39

40 Polymers Polymers are large, long-chain molecules.
Synthetic polymers are used to replace diseased veins and arteries. Polymers are large, 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, TeflonTM, and nylon. composed of small repeating units called monomers. made from reaction of small alkenes. 40

41 Common Synthetic Polymers

42 Common Synthetic Polymers

43 Common Synthetic Polymers

44 Polymerization In polymerization, small repeating units called monomers join to form a long chain polymer. monomer unit repeats n 44

45 Polymers from Addition Reactions

46 More Monomers and Polymers

47 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 7 OTHER Other plastic: fiberglass, polycarbonate, etc. 47

48 Chapter 11 Unsaturated Hydrocarbons
11.5 Aromatic Compounds 48 48

49 Benzene, or benzol, is an compound with the molecular formula C6H6
Benzene, or benzol, is an compound with the molecular formula C6H6. It is sometimes abbreviated Ph–H. Michael Faraday (1791 –1867 ) first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen. 1820 The empirical formula for benzene was long known, but its highly polyunsaturated structure, with just one hydrogen atom for each carbon atom, was challenging to determine. Several in 1861 suggested possible structures that contained multiple double bonds or multiple rings, but the study of aromatic compounds was in its very early years, and too little evidence was then available to help chemists decide on any particular structure.

50 Friedrich Auguste Kekulé

51 Aromatic Compounds Benzene is an aromatic compound.
a ring of 6 C atoms and 6 H atoms. a flat ring structure drawn with three double bonds. represented by two structures because the electrons are shared among all the C atoms. 51 51

52 Benzene Structure Benzene
has 6 electrons shared equally among the 6 C atoms. is also represented as a hexagon with a circle drawn inside. 52 52

53 Aromatic Compounds in Nature and Health
Vanillin Aspirin Ibuprofen Acetaminophen 53 53

54 Naming Aromatic Compounds
Aromatic compounds are named with benzene as the parent chain. with one side group named in front of benzene. Methylbenzene Chlorobenzene 54 54

55 Some Common Names Some substituted benzene rings
have common names that have been in use for many years. with a single substituent use a common name or are named as a benzene derivative. 55 55

56 Naming Aromatic Compounds
When two or more groups are attached to the benzene ring, the ring is numbered to give the lowest numbers to the side groups. 56 56

57 Naming Aromatic Compounds
When a common name such as aniline, phenol, or toluene can be used, the carbon atom attached to the amine, hydroxyl, or methyl group is numbered as carbon #1. Then the modifiers are named alphabetically. 57 57

58 Aromatic Compounds with Two Substituents
The position of the two groups can be indicated by numbering the ring carbons, or by using the designations in the figure at left.

59 Examples of naming with two groups:
1,3-dichlorobenzene (meta-dichlorobenzene or m-dichlorobenzene) 2-bromotoluene (ortho-bromotoluene or o-bromotoluene) 1-bromo-4-chlorobenzene (para-bromochlorobenzene or p-bromochlorobenzene)

60 Naming Example chlorobenzene 1,3-dimethylbenzene
The correct name for each compound is. chlorobenzene 1,3-dimethylbenzene (meta-dimethylbenzene) 60 60

61 Learning Check Write the structural formulas for each of the following: A. 1,3-dichlorobenzene B. ortho-chlorotoluene 61 61

62 Polycyclic Aromatic Hydrocarbons PAHs
mothballs dyes carcinogen Product of combustion of coal tar, tobacco smoke, barbecued meats. Potent carcinogen

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