Chemeketa Community College Chapter 11: Unsaturated Hydrocarbons Larry Emme Chemeketa Community College

Chapter Outline Alkenes & Alkynes Cis-Trans Isomers Reactions Polymers Aromatic Compounds

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

Unsaturated Hydrocarbons have fewer hydrogen atoms attached to the carbon chain than alkanes. are alkenes or olefins with double bonds. are alkynes or acetylenes with triple bonds. First member of each family must have two carbons

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

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 © 2009 by Pearson Education, Inc.

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

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 CH3─CH2─CC─CH3 2-pentyne 5 4 3 2 1

Guide to Naming Alkenes and Alkynes

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

Learning Check Answers 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 1 2 3 4 1-butene 1 2 3 4 2-butene 2-methyl-2-butene 4 3 2 1 2-butyne 1 2 3 4

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

Learning Check Answers Write the IUPAC name for each of the following: A. CH3─CH2─C≡C─CH3 B. CH3─CH2─C=CH─CH3 2-pentyne 5 4 3 2 1 CH3  3-methyl-2-pentene 5 4 3 2 1

Name this compound: Learning Check Write the IUPAC name for the following:

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

Fragrant Alkenes

Cis-Trans Isomers 17

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 18

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]”. 19

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. 20

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) H Br H H 21

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. 22

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 23

Is the compound below the cis or trans isomer? Learning Check Is the compound below the cis or trans isomer?

Is the compound below the cis or trans isomer? Learning Check Answers Is the compound below the cis or trans isomer? 1 2 3 4 5 trans-3-methyl-2-pentene

Other Alkenes ter ter Samantha H C C C C H H H Ashley

Learning Check Name each, using cis-trans prefixes when needed. 27

Learning Check Answers cis-1,2-Dibromoethene 1 2 1 trans-2-Butene 2 3 4 3 1,1-Dichloropropene 2 1 28

Addition Reactions 29

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. 30

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.

Addition of X2 Halogenation Examples

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.

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. 34

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. 35

Reaction Example Write an equation for the hydrogenation of 1-butene using a platinum catalyst. Pt CH2=CH─CH2─CH3 + H2 CH3─CH2─CH2─CH3 36

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. 37

Learning Check Write the product of each the following: Pt CH3─CH=CH─CH3 + H2 + H2 38

Learning Check Answers Pt 1. CH3─CH=CH─CH3 + H2 CH3─CH2─CH2─CH3 2. + H2 39

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 40

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! 41

Learning Check Write the product for the hydration of each of the following: H+ 1. CH3─CH2─CH=CH─CH2─CH3 + HOH CH3 │ H+ 2. CH3─C=CH─CH2─CH3 + HOH 3. + HOH 42

Learning Check Answers H OH │ │ 1. CH3─CH2─CH─CH─CH2─CH3 CH3 │ 2. CH3─C─CH─CH2─CH3 │ │ OH H OH 3. H 43

Polymers of Alkenes 44

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. 45

Common Synthetic Polymers 46

Common Synthetic Polymers 47

Common Synthetic Polymers 48

Polymerization In polymerization, small repeating units called monomers join to form a long chain polymer. monomer unit repeats n 49

Polymers from Addition Reactions 50

More Monomers and Polymers 51

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. 52

Aromatic Compounds 53 53

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. 6 bonds ?

Friedrich Auguste Kekulé 1829-1896

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. 56 56

Benzene Structure Benzene has 6 electrons shared equally among the 6 C atoms. is also represented as a hexagon with a circle drawn inside. 57 57

Aromatic Compounds in Nature and Health Vanillin Aspirin Ibuprofen Acetaminophen 58 58

Naming Aromatic Compounds Aromatic compounds are named with benzene as the parent chain. with one side group named in front of benzene. Methylbenzene Chlorobenzene 59 59

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. 60 60

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. 1 1 1 2 3 4 61 61

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. 1 1 1 2 2 2 6 3 3 5 3 4 4 62 62

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.

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

Learning Check The correct name for each compound is. 65 65

Learning Check Answers The correct name for each compound is. chlorobenzene 1,3-dimethylbenzene (meta-dimethylbenzene) 66 66

Learning Check Write the structural formulas for each of the following: A. 1,3-dichlorobenzene B. ortho-chlorotoluene 67 67

Learning Check Answers Write the structural formulas for each of the following: A. 1,3-dichlorobenzene B. ortho-chlorotoluene 68 68

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

The End

End of Chapter Learning Checks Try these after you have reviewed the chapter

Learning Check What is the structural formula of 4-methyl-2-pentene?

Learning Check Answers What is the structural formula of 4-methyl-2-pentene? The name indicates: Five carbons in the longest chain containing the double bond. The double bond is between carbons #2 and #3 A methyl group is on carbon #4.

Learning Check Draw the chemical structure of cis-5-chloro-2-hexene.

Learning Check Answers Draw the chemical structure of cis-5-chloro-2-hexene. This molecule contains six carbons with a C=C between carbons #2 and #3, and a Cl atom on carbon #5.

Learning Check Answers Draw the chemical structure of cis-5-chloro-2-hexene. This molecule is also cis because the carbon atoms in the longest chain containing the double bond are on the same side of the double bond.

Learning Check Is this the cis or trans isomer of 3-methyl-2-pentene?

Learning Check Answers Is this the cis or trans isomer of 3-methyl-2-pentene? This is trans-3-methyl-2-pentene because the carbon atoms in the longest chain are on opposite sides of the double bond.

Learning Check Name the following compound.

Learning Check Answers Name the following compound. 1-bromo-4-methylcyclohexene

Learning Check Name the following compounds.

Learning Check Answers Name the following compounds. 3-methyl-1-butyne 1-chloro-2-butyne

Learning Check Name the following compounds.

Learning Check Answers Name the following compounds. 1-chloro-2-bromo-4-nitrobenzene 1-ethyl-2-fluorobenzene or ortho-ethylfluorobenzene 3-nitrotoluene or meta-nitrotoluene

Learning Check What are some common uses of polyethylene? 85 85

Learning Check Answers What are some common uses of polyethylene? Packing materials, molded articles, plastic films, garbage bags, flexible bottles, containers and toys. 86 86

Learning Check What does the “PP” stand for in the symbol below? 87 87

Learning Check Answers What does the “PP” stand for in the symbol below? This is the identification code for polypropylene. “PP” stands for polypropylene. 88 88

Learning Check What does the “PS” stand for in the symbol below? 89 89

Learning Check Answers What does the “PS” stand for in the symbol below? This is the identification code for polystyrene. “PS” stands for polystyrene. 90 90