Chapter 11 Unsaturated Hydrocarbons. Saturated Hydrocarbons. Bond Angles in Alkenes and Alkynes. Unsaturated Hydrocarbons.

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1 Chapter 11 Unsaturated ydrocarbons 11.1 Alkenes and Alkynes Saturated ydrocarbons Saturated hydrocarbons have the maximum number of hydrogen atoms attached to each carbon atom. are alkanes and cycloalkanes with single C-C bonds. C 3 C 2 C Unsaturated ydrocarbons Unsaturated hydrocarbons have fewer hydrogen atoms attached to the carbon chain than alkanes. are alkenes with double bonds. are alkynes with triple bonds. Bond Angles in Alkenes and Alkynes According to VSEPR theory: the three groups bonded to carbon atoms in a double bond are at 120 angles. alkenes are flat because the atoms in a double bond all lie in the same plane. the two groups bonded to each carbon in a triple bond are at 180 angles. 3 4 Naming Alkenes Ethene (Ethylene) The names of alkenes use the corresponding alkane name. change the ending to ene. Alkene IUPAC Common 2 C=C 2 ethene ethylene 2 C=C C 3 propene propylene cyclohexene Ethene, or ethylene, is an alkene with the formula C 2 4. has two carbon atoms connected by a double bond. has two atoms bonded to each C atom. is flat with all the C and atoms in the same plane. is used to accelerate the ripening of fruits. 5 6

2 Naming Alkynes Naming Alkenes and Alkynes The names of alkynes use the corresponding alkane name. change the ending to yne. Alkyne IUPAC Common C C ethyne acetylene C C C 3 propyne 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. C 2 =C C 2 C 3 1-butene C 3 C=C C C 3 C 2 C C C butene 2-pentyne 7 8 Guide to Naming Alkenes and Alkynes Write the IUPAC name for each of the following: 1. C 2 =C C 2 C 3 2. C 3 C=C C 3 C 3 3. C 3 C=C C 3 4. C 3 C C C Write the IUPAC name for each of the following: 1. C 2 =C C 2 C 3 1-butene 2. C 3 C=C C 3 2-butene C 3 3. C 3 C=C C 3 2-methyl-2-butene Write the IUPAC name for each of the following: A. C 3 C 2 C C C 3 C 3 B. C 3 C 2 C=C C 3 4. C 3 C C C 3 2-butyne 11 12

3 Write the IUPAC name for each of the following: A. C 3 C 2 C C C 3 2-pentyne Chapter 11 Unsaturated ydrocarbons 11.2 Cis-Trans Isomers C 3 B. C 3 C 2 C=C C 3 3-methyl-2-pentene Copyright 2009 by Pearson Education Cis and Trans Isomers Cis-Trans Isomers In an alkene, the double bond is rigid. holds attached groups in fixed positions. makes cis-trans isomers possible. 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 Cis-Trans Isomerism Two isomers are possible when groups are attached to the double bond are different. In a cis isomer, the alkyl groups are attached on the one side of the double bond and atoms are on the other side. In the trans isomer, the groups and atoms are attached on opposite sides. Alkenes cannot have cis-trans isomers if a carbon atom in the double bond is attached to identical groups. C C Identical Identical Br Br C C C 3 Br 2-Bromopropene (not cis or trans) 1,1-Dibromoethene (not cis or trans) 17 18

4 Cis-Trans Isomers in Nature Naming Cis-Trans Isomers 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. 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 Br C C Br Br C C Br cis-1,2-dibromoethene trans-1,2-dibromoethene Name each, using cis-trans prefixes when needed. Br Br A. C C C 3 B. C C C 3 C 3 C. C C A. B. C. Br Br C C C 3 C C C 3 C 3 C C cis-1,2-dibromoethene trans-2-butene 1,1-Dichloropropene Chapter 11 Unsaturated ydrocarbons 11.3 Addition Reactions 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

5 ydrogenation ydrogenation of Oils In hydrogenation, hydrogen atoms add to the carbon atoms of a double bond or triple bond. a catalyst such as or Ni is used to speed up the reaction. 2 C C C C Ni 2 C C 2 C C Adding 2 to double bonds in vegetable oils produces compounds with higher melting points. solids at room temperature, such as margarine, soft margarine, and shortening Write an equation for the hydrogenation of 1-butene using a platinum catalyst. Write an equation for the hydrogenation of 1-butene using a platinum catalyst. C 2 =C C 2 C C 3 C 2 C 2 C 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. (1) True or (2) False A. There are more unsaturated fats in vegetable oils than in animal fats. B. ydrogenation converts some cis-double bonds to trans-double bonds. C. Animal fats have more unsaturated fats than vegetable oils

6 (1) True or (2) False Write the product of each the following: A. 1_ There are more unsaturated fats in vegetable oils than in animal fats. B. 1_ ydrogenation converts some cis-double bonds to trans-double bonds. C. 2_ Animal fats have more unsaturated fats than vegetable oils. C 3 C=C C ydration 1. C 3 C=C C C 3 C 2 C 2 C In the addition reaction called hydration, an acid + catalyst is required. water (O) adds to a double bond. an atom bonds to one C in the double bond. an O bonds to the other C. O + C 3 C=C C 3 + O C 3 C C C ydration When hydration occurs with a double bond that has an unequal number of atoms, the atom bonds to the C in the double bond with the more. the O bonds to the C in the double bond with the fewer atoms. O + C 3 C=C 2 + O C 3 C C 2 Write the product for the hydration of each of the following: + 1. C 3 C 2 C=C C 2 C 3 + O C C 3 C=C C 2 C 3 + O 3. + O

7 O 1. C 3 C 2 C C C 2 C 3 C 3 2. C 3 C C C 2 C 3 O O 3. Chapter 11 Unsaturated ydrocarbons 11.4 Polymers of Alkenes Polymers Common Synthetic 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 Common Synthetic Polymers Common Synthetic Polymers Copyright 2009 Pearson Education, Inc. Copyright 2009 Pearson Education, Inc

8 Polymerization Polymers from Addition Reactions In polymerization, small repeating units called monomers join to form a long chain polymer. C C + C C + C C Ethylene monomers chain continues monomer unit repeats C C C C C C chain continues n Polyethylene More Monomers and Polymers What is the starting monomer for polyethylene? Ethene (ethylene) Name the monomer used to make Teflon, and write a portion of a Teflon polymer using four monomers. C 2 =C

9 F F F C=C F F F F F F F F F C C C C C C C C F F F F F F F F tetrafluoroethene portion of Teflon Recycling Plastics Recycling is simplified by using codes on plastic items. 1 PETE Polyethyleneterephtalate 2 DPE igh-density polyethylene 3 PV Polyvinyl chloride 4 LDPE Low-density polyethylene 5 PP Polypropylene 6 PS Polystyrene 7 OTER Other plastic: fiberglass, polycarbonate, etc What types of plastic are indicated by the following codes? What types of plastic are indicated by the following codes? A. B. C. 3 PV 5 PP 6 PS 3 A. PV Polyvinyl chloride B. 5 Polypropylene PP C. Polystyrene 6. PS Chapter 11 Unsaturated ydrocarbons 11.5 Aromatic Compounds Aromatic Compounds Benzene is an aromatic compound. a ring of 6 C atoms and 6 atoms. a flat ring structure drawn with three double bonds. represented by two structures because the electrons are shared among all the C atoms. Copyright 2009 Pearson Education, Inc. Copyright 2009 Pearson Education, Inc

10 Benzene Structure Benzene has 6 electrons shared equally among the 6 C atoms. is also represented as a hexagon with a circle drawn inside. Aromatic Compounds in Nature and ealth Vanillin O C Aspirin O CO O C O C 3 O OC 3 O Ibuprofen Acetaminophen N C C 3 3 C C 3 C C 2 C 3 O C CO O Copyright 2009 Pearson Education, Inc Naming Aromatic Compounds Some Common Names Aromatic compounds are named with benzene as the parent chain. with one side group named in front of benzene. C 3 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. C 3 N 2 O Methylbenzene Chlorobenzene Toluene Aniline Phenol (methylbenzene) (benzenamine) (hydroxybenzene) Naming Aromatic Compounds When two groups are attached to the benzene ring, the ring is numbered to give the lowest numbers to the side groups. C 3 O 3-Chlorotoluene 1,4-Dichlorobenzene 2-Chlorophenol Select the correct name for each compound. 1) chlorocyclohexane 2) chlorobenzene 3) 1-chlorobenzene C 3 C 3 1) 1,2-dimethylbenzene 2) 1,4-dimethylbenzene 3) 1,3-dimethylbenzene 59 60

11 Select the correct name for each compound. 2) chlorobenzene Write the structural formulas for each of the following: A. 1,3-dichlorobenzene B. 2-chlorotoluene C 3 3) 1,3-dimethylbenzene C Write the structural formulas for each of the following: A. 1,3-dichlorobenzene Identify the organic family for each: A. C 3 C 2 C=C 2 B. B. 2-chlorotoluene C 3 C. C 3 C C D Identify the organic family for each: A. C 3 C 2 C=C 2 alkene B. cycloalkane (alkane) C. C 3 C C alkyne D. aromatic 65