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1 Chapter 11 Unsaturated Hydrocarbons 11.1 Alkenes and Alkynes.

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1 1 Chapter 11 Unsaturated Hydrocarbons 11.1 Alkenes and Alkynes

2 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 3 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

4 4 Naming Alkenes The names of alkenes use the corresponding alkane name. change the ending to –ene. AlkeneIUPACCommon H 2 C=CH 2 ethene ethylene H 2 C=CH─CH 3 propene propylene cyclohexene

5 5 Ethene (Ethylene ) Ethene, or ethylene, is an alkene with the formula C 2 H 4. 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 © 2009 by Pearson Education, Inc.

6 6 Naming Alkynes The names of alkynes use the corresponding alkane name. change the ending to –yne. Alkyne IUPACCommon HC ≡ CH ethyne acetylene HC ≡ C─CH 3 propyne

7 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. CH 2 =CH─CH 2 ─CH 3 1-butene CH 3 ─CH=CH─CH 3 2-butene CH 3 ─CH 2 ─C  C─CH 3 2-pentyne

8 Guide to Naming Alkenes and Alkynes 8

9 9 Learning Check Write the IUPAC name for each of the following: 1. CH 2 =CH─CH 2 ─CH 3 2. CH 3 ─CH=CH─CH 3 CH 3 | 3. CH 3 ─CH=C─CH 3 4. CH 3 ─C  C─CH 3

10 10 Solution Write the IUPAC name for each of the following: 1. CH 2 =CH─CH 2 ─CH 3 1-butene 2. CH 3 ─CH=CH─CH 3 2-butene CH 3 | 3. CH 3 ─CH=C─CH 3 2-methyl-2-butene 4. CH 3 ─C  C─CH 3 2-butyne

11 11 Learning Check Write the IUPAC name for each of the following: A. CH 3 ─CH 2 ─C ≡ C─CH 3 CH 3  B. CH 3 ─CH 2 ─C=CH─CH 3

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

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

14 Fragrant Alkenes 14

15 15 Chapter 11 Unsaturated Hydrocarbons 11.2 Cis-Trans Isomers

16 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

17 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]”.

18 18 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

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

20 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.

21 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. cistrans cis-1,2-Dibromoethene trans-1,2-Dibromoethene

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

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

24 24 Chapter 11 Unsaturated Hydrocarbons 11.3 Addition Reactions

25 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.

26 26 Addition of X 2 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 27 Addition of X 2 Halogenation Examples

28 28 Addition of X 2 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 29 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

30 30 Adding H 2 to double bonds in vegetable oils produces compounds with higher melting points. solids at room temperature, such as margarine, soft margarine, and shortening. Hydrogenation of Oils

31 31 Reaction Example Write an equation for the hydrogenation of 1-butene using a platinum catalyst. Pt CH 2 =CH─CH 2 ─CH 3 + H 2 CH 3 ─CH 2 ─CH 2 ─CH 3

32 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.

33 33 Learning Check Write the product of each the following: Pt CH 3 ─CH=CH─CH 3 + H 2 Pt + H 2

34 34 Solution Pt 1. CH 3 ─CH=CH─CH 3 + H 2 CH 3 ─CH 2 ─CH 2 ─CH 3 Pt 2. + H 2

35 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 + │ │ CH 3 ─CH=CH─CH 3 + H─OH CH 3 ─CH─CH─CH 3

36 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 + │ │ CH 3 ─CH=CH 2 + H─OH CH 3 ─CH─CH 2 Them that has, gets! C has 1 HC has 2 H’s

37 37 Learning Check Write the product for the hydration of each of the following: H + 1. CH 3 ─CH 2 ─CH=CH─CH 2 ─CH 3 + HOH CH 3 │ H + 2. CH 3 ─C=CH─CH 2 ─CH 3 + HOH H HOH

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

39 39 Chapter 11 Unsaturated Hydrocarbons 11.4 Polymers of Alkenes

40 40 Polymers 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, Teflon TM, and nylon. composed of small repeating units called monomers. made from reaction of small alkenes. Synthetic polymers are used to replace diseased veins and arteries.

41 41 Common Synthetic Polymers

42 42 Common Synthetic Polymers

43 43 Common Synthetic Polymers

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

45 45 Polymers from Addition Reactions

46 46 More Monomers and Polymers

47 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.

48 48 Chapter 11 Unsaturated Hydrocarbons 11.5 Aromatic Compounds

49 49 Benzene, or benzol, is an compound with the molecular formula C 6 H 6. 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. 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. 1820

50 Friedrich Auguste Kekulé

51 51 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. Aromatic Compounds

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

53 53 Aromatic Compounds in Nature and Health VanillinAspirin Ibuprofen Acetaminophen

54 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

55 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.

56 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.

57 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.

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) 1-bromo-4-chlorobenzene (para-bromochlorobenzene or p-bromochlorobenzene) 2-bromotoluene (ortho-bromotoluene or o-bromotoluene)

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

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

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


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