Chapter 12 Unsaturated Hydrocarbons 12.1 Alkenes and Alkynes Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Unsaturated Hydrocarbons • Have fewer hydrogen atoms attached to the carbon chain than alkanes. • Are alkenes with double bonds. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings • Are alkynes with triple bonds.

Bond Angles in Alkenes and Alkynes According to VSEPR theory: • Three groups in a double bond are bonded at 120° angles. • Alkenes are flat, because the atoms in a double bond lie in the same plane. • The groups attached to a triple bond are at 180° Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings angles.

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 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 © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

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

Guide to Naming Alkenes and Alkynes Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Naming Alkenes Write the IUPAC name for CH2=CH ─CH2 ─CH3 and STEP 1 Name the longest carbon chain butene STEP 2 Number the chain from the double bond CH2=CH ─CH2 ─CH3 1-butene 1 2 3 4 CH3 ─CH=CH ─CH3 2-butene

Comparing Names of Alkanes, Alkenes, and Alkynes TABLE 12.1 Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Naming Alkenes with Substituents CH3 │ Write the IUPAC name for CH3 ─CH ─CH=CH ─CH3 STEP 1 Name the longest carbon chain pentene STEP 2 Number the chain from the double bond CH3 │ CH3 ─CH ─CH=CH ─CH3 2-pentene 5 4 3 2 1 STEP 3 Give the location of each substituent 4-methyl- 2-pentene

Naming Alkynes with Substituents CH3 │ Write the IUPAC name for HC ≡C ─CH ─CH3 1 2 3 4 STEP 1 Name the longest carbon chain butyne STEP 2 Number the chain from the double bond 1-butyne STEP 3 Give the location of each substituent 3-methyl-1-butyne

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

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

Learning Check Write the structural formula for each of the following: 2-pentyne B. 3-methyl-2-pentene

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

Chapter 12 Unsaturated Hydrocarbons 12.2 Cis-Trans Isomers Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Cis and Trans Isomers In an alkene, cis and trans isomers are possible because the double bond • Is rigid. • Cannot rotate. • Has groups attached to the carbons of the double bond that are fixed relative to each other. CH3 CH3 CH3 CH = CH CH = CH cis trans CH3

Cis-Trans Isomers Cis-trans isomers • Can be modeled by making a “double bond” with your fingers with both thumbs on the same side or opposite from each other. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Cis-Trans Isomers Cis-trans isomers occur when different 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. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Cis-Trans Isomerism H Br C C C C H CH3 Br • Cis-trans isomers do not occur if a carbon atom in the double bond is attached to identical groups. Identical Identical H Br H Br C C C C H CH3 Br H 2-bromopropene 1,1-dibromoethene (not cis or trans) (not cis or trans)

Naming Cis-Trans Isomers • The prefixes cis or trans are placed in front of the alkene name when there are cis-trans isomers. cis trans Br Br Br H C C C C H Br H H cis-1,2-dibromoethene trans-1,2-dibromoethene

Pheromones A pheromone • Is a chemical messenger emitted by insects in tiny quantities. • Called bombykol emitted by the silkworm moth to attract other moths has one cis and one trans double Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check Name each, using cis-trans prefixes when needed. Br Br C C H H CH3 H B. C C H CH3 CH3 Cl C. C C H Cl

Solution cis-1,2-dibromoethene trans-2-butene 1,1-dichloropropene Br C C cis-1,2-dibromoethene H H CH3 H B. C C trans-2-butene H CH3 CH3 Cl C. C C H Cl 1,1-dichloropropene Identical atoms on one C; no cis or trans

Chapter 12 Unsaturated Hydrocarbons 12.5 Aromatic Compounds Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Benzene Structure Benzene • Has 6 electrons shared equally among the 6 C atoms. • Is also represented as a hexagon with a circle drawn inside. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Aromatic Compounds in Nature and Health Vanillin O Aspirin O CH COH O C O CH3 OCH3 O OH NH C CH3 Ibuprofen Acetaminophen CH3 CH3 O HC CH CH2 CH COH OH 3

Naming Aromatic Compounds Aromatic compounds are named • With benzene as the parent chain. • With one side group named in front of benzene. CH3 Cl methylbenzene chlorobenzene

Some Common Names Some substituted benzene rings • Have common names used for many years. • With a single substituent use a common name or are named as a benzene derivative. CH3 NH2 OH toluene aniline phenol (methylbenzene) (benzenamine) (hydroxybenzene)

Learning Check Identify the organic family for each: A. CH3 ─CH2 ─CH=CH2 B. C. CH3 ─C ≡CH D.

Solution Identify the organic family for each: A. CH3 ─CH2 ─CH=CH2 alkene B. cycloalkane (alkane) C. CH3 ─C ≡CH alkyne D. aromatic