*Lecture 3 Unsaturated HydrocarbonsLecture OutlineClass odds and endsDefining unsaturation in hydrocarbonsNaming alkenes and alkynesCis and trans isomersReactions of alkenes and alkynesHydrogenationHalogenationHydrohalogenationhydrationPolymersAromatic compoundsProperties of aromatic compounds

*Compare the following structures of ethane, ethene and ethyne.What difference do you notice among the first and the last two structures? (Ethane is saturated and ethene and ethyne are unsaturated?How would you define unsaturated hydrocarbons? Unsaturated Hydrocarbons

* Bond Angles in Alkenes and AlkynesAccording 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 angles.Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

*Naming AlkenesLook and study the names of the following alkenesAlkene IUPACCommonH2C=CH2 ethene ethyleneH2C=CHCH3 propene propylene cyclohexeneCH2=CHCH2CH3 1-buteneCH3CH=CHCH3 2-buteneHow is the naming of alkenes done? Talk over with your group members

*Naming AlkynesNow, lets look at the case of alkynes. Naming is done in a fashion similar to that of alkenes.AlkyneIUPACCommonHCCHethyne acetyleneHCCCH3propyne4-Bromo-2-pentynecycloheptyne

*Naming Alkenes and Alkynes with SubstituentsNow what if the alkene or alkyne has a substituent? Here is an example. Write the IUPAC name for CH3 CH3CHCH=CHCH3

*Naming Alkynes with SubstituentsWrite the IUPAC name for CH3 HCCCHCH3

*Summary: Naming Alkenes and AlkynesOkay, so lets summarize the rules for naming alkenes and alkynes. Here is what we do:

Name the longest carbon chain with a double or triple bondIndicate the location of the double or triple bond in the main chain by number, starting at the end closer to the double or triple bondCycloalkenes do not require the numerical prefix but the bonds are given numbers 1 and 2Give the location and name of each substituent (alphabetical order) as a prefix to the name

*Learning CheckWrite the IUPAC name for each of the following: 1. CH2=CHCH2CH32. CH3CH=CHCH3 CH3 |3. CH3CH=CCH3 4. CH3CCCH3

Solution____________________________

______________

______________

*Learning CheckWrite the structural formula for each of the following:

A. 2-pentyne

3-methyl-2-pentene

Solution_______________

________________

*Cis and Trans IsomersIn an alkene, cis and trans isomers are possiblebecause the double bond Is rigid.Cannot rotate. Has groups attached to the carbons of the double bond that are fixed relative to each other. CH3CH3 CH3

CH = CH CH = CH cis trans CH3

*Cis-trans isomers occur whendifferent groups are attached tothe 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.Cis-Trans IsomersCopyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

*Cis-Trans IsomerismCis-trans isomers do not occur 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 H H Br

*Naming Cis-Trans Isomers The prefixes cis or trans are placed in front of the alkene name when there are cis-trans isomers. cistrans

cis-1,2-dibromoethene trans-1,2-dibromoethene

*Learning CheckName each, using cis-trans prefixes when needed.

*Lecture 3 Unsaturated Hydrocarbons

Reactions of Alkenes and AlkynesCopyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

*Addition ReactionsThere are four addition reactions we will study, summarized in table 12.2TABLE 12.2

*Question: what happens in hydrogenation? Study the examples given below to answer this question?(Side note: a catalyst such as Pt or Ni is used to speed up the reaction)HydrogenationYour conclusion about hydrogenation:

*Adding H2 to doublebonds in vegetableoils producesCompounds with higher melting points.Solids at room temperature such as margarine, soft margarine, and shortening.

Hydrogenation of OilsCopyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

*Learning Check Write an equation for the hydrogenation of 1-butene using a platinum catalyst.

*Trans FatsIn vegetable oils, the unsaturated fats usually containcis 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.

*Learning Check Write the product of each the following reactions: PtCH3CH=CHCH3 + H2

Pt + H2

*HalogenationQuestion: What happens in halogenation reaction? Think about the following reactions.

Your conclusion about halogenation of alkenes and alkynes is that

*Write the product of the following addition reactions: 1. CH3CH=CHCH3 + Cl2

2. Learning Check

*Testing for UnsaturationWhen bromine (Br2) is added to an alkane, the red color of bromine persists.

When bromine (Br2) is added to an alkene or alkyne, the red color of bromine disappears immediately. Br2Br2Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings15

*HydrohalogenationWhat happens in hydrohalogenation reactions? Again, think about where atoms of a hydrogen halide end up.

*Markovnikovs RuleWhen an unsymmetrical alkene undergoes hydrohalogenation, the H in HX adds to the carbon in the double bond that has the greater number of H atoms .

*HydrationIn the addition reaction called hydrationAn 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+ CH3CH=CHCH3 + HOH CH3CHCHCH3

*HydrationWhen hydration occurs with a double bond that has anunequal number of H atoms,The H atom bonds to the C in the double bond with the most H.The OH bonds to the C in the double bond with the fewest H atoms. OH H H+ CH3CH=CH2 + HOH CH3CHCH2 (1H) (2H)

*Learning CheckWrite the product for the hydration of each of the following: H+1. CH3CH2CH=CHCH2CH3 + HOH CH3 H+2. CH3C=CHCH2CH3 + HOH

H+3. + HOH

*Learning CheckWrite the products of each reaction

*PolymersPolymers 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, and nylon.Made up of small repeating units called monomers.Made by reaction of small alkenes.

*PolymerizationIn polymerization, small repeating units called monomers join to form a long chain polymer. monomer unit repeatsn

*Common Synthetic Polymers

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

*Polymers from Addition ReactionsTABLE 12.3

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

*More Monomers and Polymers

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

*Learning CheckWhat is the starting monomer for polyethylene?

*Learning CheckName the monomer used to make Teflon and write aportion of a Teflon polymer using four monomers.

*Recycling PlasticsRecycling is simplified by using codes found on plastic items.

1 PETE Polyethyleneterephtalate2 HDPE High-density polyethylene3 PV Polyvinyl chloride4 LDPE Low-density polyethylene5 PP PolypropylenePS Polystyrene

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

*Lecture 3 Unsaturated Hydrocarbons

Aromatic Compounds

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

*Benzene Has 6 electrons shared equally among the 6 C atoms.Is also represented as a hexagon with a circle drawn inside.Benzene Structure

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

*Aromatic Compounds in Nature and Health Vanillin Aspirin

Ibuprofen Acetaminophen

*Naming Aromatic CompoundsAromatic compounds are namedWith benzene as the parent chain. With one side group named in front of benzene.

methylbenzene chlorobenzene

*Some Common NamesSome substituted benzene ringsHave common names used for many years.With a single substituent use a common name or are named as a benzene derivative.

toluene aniline phenol (methylbenzene) (benzenamine) (hydroxybenzene)

*Aromatic Compounds with Two GroupsTwo naming systems are used when two groups areattached to a benzene ring. Number the ring to give the lowest numbers to the side groups.Use prefixes to show the arrangement: ortho(o-) for 1,2- meta(m-) for 1,3- para(p-) for 1,4-

*Aromatic Compounds with Two Groups

3-chlorotoluene 1,4-dichlorobenzene 2-chlorophenolm-chlorotoluenep-dichlorobenzene o-chlorophenol

*Learning CheckSelect the correct name for each compound:1) chlorocyclohexane2) chlorobenzene3) 1-chlorobenzene

1) 1,2-dimethylbenzene2) m-xylene3) 1,3-dimethylbenzene

*Learning Check Write the structural formulas for each of the following:A. 1,3-dichlorobenzene

B. o-chlorotoluene

*Learning Check Identify the organic family for each:

A. CH3CH2CH=CH2

B.

C. CH3CCH

D.

*Properties of Aromatic CompoundsAromatic compoundsHave a stable aromatic bonding system.Are resistant to many reactions. Undergo substitution reactions, which retain the stability of the aromatic bonding system.

*Substitution ReactionsIn a substitution reaction, a hydrogen atom on a benzene ring is replaced by an atom or group of atoms. Type of substitutionH on benzene replaced byHalogenation chlorine or bromine atomNitrationnitro group (NO2) Sulfonation SO3H group

*HalogenationIn a halogenation An H atom of benzene is replaced by a chlorine or bromine atom.A catalyst such as FeCl3 is needed in chlorination.A catalyst such as FeBr3 is needed in bromination.

*NitrationIn the nitration of benzeneAn H atom of benzene is replaced by a nitro (-NO2) group from HNO3. An acid catalyst such as H2SO4 is needed.

*SulfonationIn a sulfonationAn H atom on benzene is replaced by a SO3H group from SO3. An acid catalyst such as H2SO4 is needed.

*Learning CheckWrite the equation for the bromination of benzene including catalyst.