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Chemistry 121(01) Winter 2009

Introduction to Organic Chemistry and Biochemistry Instructor Dr. Upali Siriwardane (Ph.D. Ohio State) E-mail: [email protected] Office: 311 Carson Taylor Hall ; Phone: 318-257-4941; Office Hours: MTW 9:00 am - 11:00 am; Chapter 13: Unsaturated TR 9::00 - !0:00 am & 1:00-2:00 pm.

December 19, Test 1 (Chapters 12-14) Sections 4.1-4.5 January 2 Test 1 (Chapters 15-16) February 6 (Chapters 17-19) February 27, (Chapters 20-22) March 2, 2009, Make Up Exam: Bring Scantron Sheet 882-E

Chemistry 121, Winter 2008, LA Tech 1-1 Chemistry 121, Winter 2008, LA Tech 1-2

Chapter 13: Unsaturated Hydrocarbons Unsaturated hydrocabons 13.2 Characteristics of and Hydrocarbons with carbon-carbon double bonds 13.3 Names for Alkenes and Cycloalkenes 13.4 Line-Angle Formulas for Alkenes and triple bonds 13.5 Isomerism in Alkenes 13.6 Naturally Occurring Alkenes double bonds: alkenes 13.7 Physical Properties of Alkenes 13.8 Chemical Reactions of Alkenes triple bonds: 13.9 Polymerization of Alkenes: Addition Polymers 13.10 Alkynes three alternating in 6 carbon ring: 13.11 Aromatic Hydrocarbons aromatics 13.12 Names for Aromatic Hydrocarbons 13.13 Aromatic Hydrocarbons: Physical Properties and Sources 13.14 Chemical Reactions of Aromatic Hydrocarbons 13.15 Fused-Ring Aromatic Compounds Chemical Connections: Ethene: A Plant Hormone and High-Volume Industrial Chemical; Cis-Trans Isomerism and Vision; Carotenoids: A Source of Color; Fused-Ring Aromatic Hydrocarbons and Cancer

Chemistry 121, Winter 2008, LA Tech 1-3 Chemistry 121, Winter 2008, LA Tech 1-4 Units of Unsaturation Unsaturated Hydrocarbons: Compounds that have have fewer hydrogens than H saturated hydrocarbons (C H ). Two hydrogen are Alkenes Alkynes Arenes n 2n+2 H C H considered as unit of unstauration C C C C H C H ring CnH2n (one unit of unsat.) H ethene ethyne Unsaturated hydrocarbons: C H C H C H 2 4 2 2 6 6 bond C H (one unit of unsat.) C H C H C H n 2n n 2n n 2n−2 n n bond C H (two units of unsat.) unsaturated unsaturated Aromatic n 2n−2 Arene Chapters 13 Chapters 13 Chapter 13

Chemistry 121, Winter 2008, LA Tech 1-5 Chemistry 121, Winter 2008, LA Tech 1-6

Structure of Alkenes Planar Structure of Alkenes

• Alkene: contains a carbon-carbon double bond and has According to the orbital overlap model, a double bond consists of the general formula CnH2n 2 • The two carbon atoms of a double bond and the four • a σ bond formed by overlap of sp hybrid orbitals atoms bonded to them lie in a plane, with bond angles • a π bond formed by overlap of parallel 2p orbital of approximately 120° Rotating by 90°breaks the pi bond

121.7° 124.7°

H H H CH 3 CC CC H H H H Propene

Chemistry 121, Winter 2008, LA Tech 1-7 Chemistry 121, Winter 2008, LA Tech 1-8 Structure of Alkynes The functional group of an alkyne is a carbon-carbon triple Alkenes bond A triple bond consists of Second members of the family. • one σ bond formed by the overlap of sp hybrid orbitals • contain only hydrogen and carbon • two π bonds formed by the overlap of sets of parallel 2p • have single bonds and at least one C=C double orbitals bond All members have the general formula of

CnH2n

TwiceTwice as as many many hydrogen hydrogen asas carbon carbon

Chemistry 121, Winter 2008, LA Tech 1-9 Chemistry 121, Winter 2008, LA Tech 1-10

Alkenes: Naming and Structures IUPAC Nomenclature of Alkenes and Alkynes • name the longest continuous carbon chain containing the multiple bond(s) (parent chain). If cyclic, ring is the parent. One simple class of compound is the alkene multiple bond(s) (parent chain). If cyclic, ring is the parent. which has only C, H and single bonds. • use the infix -en- to show the presence of a carbon-carbon double bond • ethene propene 2- butene • use the infix -yn- to show the presence of a carbon-carbon • C H C H C H 2 4 3 6 4 8 triple bond • CH2CH2 CH3CH2CH2 CH3CH2CHCH3 • number the parent chain to give the 1st carbon of the double/triple bond the lower number • If both double and triple are present and cannot have the same #, then double bonds take priority. • follow IUPAC general rules for numbering and naming substituents • for a , the double bond must be numbered 1,2 Chemistry 121, Winter 2008, LA Tech 1-11 Chemistry 121, Winter 2008, LA Tech 1-12 IUPAC Nomenclature of Alkynes Example of IUPAC Nomenclature of Alkenes • use the infix -yn-yn to show the presence of a carbon- carbon triple bond • number the parent chain to give the 1st carbon of the 5 3 1 triple bond the lower number 6 4 2 6 4 2 4 2 5 3 1 5 3 1 • follow IUPAC rules for numbering and naming 1-Hexene 4-Methyl-1-hexene substituents 2-Ethyl-3-methyl- 1-pentene

1 1 2 34 2 4 2 5 4 1 CH 3 3 3 3 6 7 5 CH3 4 6 CH 12 5 3 3-Methyl-1-butyne 6,6-Dimethyl-3-heptyne 3-Methylcyclo- 1,6-Dimethylcyclo- pentene hexene

Chemistry 121, Winter 2008, LA Tech 1-13 Chemistry 121, Winter 2008, LA Tech 1-14

Nomenclature of Alkenes: Common Names Alkenes

Some alkenes, particularly low-molecular-weight ones, are known almost exclusively by their common names First four members of the Name # of C Condensed formula CH 3 CH =CH CH CH= CH CH C=CH 2 2 3 2 3 2 Ethene 2 CH2=CH2 IUPAC: Ethene Propene 2-Methylpropene Co m mo n: Ethy l e ne Propylene Propene 3 CH3CH=CH2

2-Butene 4 CH3CH=CHCH3 Called a homologous series

• “Members differ by number of CH2 groups”

Chemistry 121, Winter 2008, LA Tech 1-15 Chemistry 121, Winter 2008, LA Tech 1-16 Naming alkenes and alkynes Cis and trans Geometrical isomers of alkenes Find the longest carbon chain. Use as base name with an ene or yne ending. two groups are said to be located cis to each other if they Number the chain to give lowest number for the two groups are said to be located cis to each other if they carbons of the double or triple bond. lie on the same side of a plane with respect to the double bond. Locate any branches on chain. Use base names with a yl ending. If they are on opposite sides, their relative position is described as trans. For multiple branch of the same type, modify name with di, tri, ... Show the location of each branch with numbers. List multiple branches alphabetically - the di, tri, ... don’t count..

Chemistry 121, Winter 2008, LA Tech 1-17 Chemistry 121, Winter 2008, LA Tech 1-18

Geometrical Stereoisomerism Physical Properties Because of restricted rotation about a C-C double bond, Alkenes and alkynes are nonpolar compounds groups on adjacent carbons are either cis or trans to • the only attractive forces between their molecules are each other dispersion forces Their physical properties are similar to those of alkanes of similar carbon skeletons H H H CH3 • those that are liquid at room temperature are less dense C C C C than water (1.0 g/m L)

H3 C CH3 H3 C H • they dissolve in each other and in nonpolar organic solvents cis-2-Butene trans-2-Butene mp -139°C, bp 4°C mp -106°C, bp 1°C • they are insoluble in water

Chemistry 121, Winter 2008, LA Tech 1-19 Chemistry 121, Winter 2008, LA Tech 1-20 Cis-Trans Isomerism • trans alkenes are more stable than cis alkenes because Geometric isomers of nonbonded interaction strain between alkyl substituents of the same side of the double bond There are two possible arrangements. Example 2-butene

H3C CH3 H3C H C=C C=C H H H CH3

cis trans Largest groups are Largest groups are on the same side. on opposite sides.

Chemistry 121, Winter 2008, LA Tech 1-21 Chemistry 121, Winter 2008, LA Tech 1-22

Cis-Trans Isomerism in Cycloalkenes Cis-Trans Isomerism • the configuration of the double bond in through , trienes, and polyenes cycloheptene must be cis; these rings are not large enough to accommodate a trans double bond • for an alkene with n carbon-carbon double bonds, each of which can show cis-trans isomerism, 2n cis-trans H CH3 isomers are possible • consider 2,4-heptadiene; it has four cis-trans isomers, H C H3 • cyclooctene is the smallest cycloalkene that can accommodate a two of which are drawn here trans double bond Double bond 2 2 C2 -C3 C4 -C5 4 4 trans trans trans ci s cis trans trans,trans-2,4- trans,cis-2,4- cis cis heptadiene heptadiene

trans-Cy clo octene cis-Cyclooctene Chemistry 121, Winter 2008, LA Tech 1-23 Chemistry 121, Winter 2008, LA Tech 1-24 Naturally Occurring Naturally Occurring Alkenes: The Terpenes AlkenesCis-Trans Isomerism Terpene: a compound whose carbon skeleton can be • vitamin A has five double bonds divided into two or more units identical with the carbon skeleton of isoprene • four of the five can show cis-trans isomerism

• vitamin A is the all-trans isomerenzyme- catalyzed oxidation OH

Vitamin A (retinol) O head2 4 tail H 1 3 2-Methyl-1,3- Vitamin A aldehyde (retinal) (Isoprene)

Chemistry 121, Winter 2008, LA Tech 1-25 Chemistry 121, Winter 2008, LA Tech 1-26

Terpenes: Polymers of Isoprene Terpenes Vitamin A (retinol)

• myrcene, C10H16, a • the four isoprene units in vitamin A are shown in red component of bayberry • they are linked head to tail, and cross linked at one wax and oils of bay and verbena point (the blue bond) to give the six-membered ring

• menthol, from peppermint

OH OH

Chemistry 121, Winter 2008, LA Tech 1-27 Chemistry 121, Winter 2008, LA Tech 1-28 Reactions of alkenes Addition Reactions The exposed electrons of double bonds make Combustion alkenes more reactive than alkanes and show addition reactions. C2H4 + 4 O2 2 CO2 + 2 H2O + heat

Alkynes also under go combustion reactions similarly

Chemistry 121, Winter 2008, LA Tech 1-29 Chemistry 121, Winter 2008, LA Tech 1-30

Halogenation

Halogenation - Addition of halogen to the double bond. Textbook page xx.

Chemistry 121, Winter 2008, LA Tech 1-31 Chemistry 121, Winter 2008, LA Tech 1-32 Hydrogenation

Addition of hydrogen to the double bond. Textbook page 84

Chemistry 121, Winter 2008, LA Tech 1-33 Chemistry 121, Winter 2008, LA Tech 1-34

Hydration

Addition of water to the double bond. Textbook page86.

Chemistry 121, Winter 2008, LA Tech 1-35 Chemistry 121, Winter 2008, LA Tech 1-36 Markovnikov Rule Non symmetric alkene In hydrohalogenation and hydration reations hydrogen adds to the double-bonded carbon with the most hydrogens

Chemistry 121, Winter 2008, LA Tech 1-37 Chemistry 121, Winter 2008, LA Tech 1-38

Polymerization

Formula Name Monomer Polymer

Polypropylene CH3CH=CH2 ( CH-CH 2 ) |

CH3

Polystyrene -CH=CH2 ( CH-CH 2 )

Polychloroprene H2C=CHC=CH2 ( CH 2 CH=CCH 2 ) | | Chemistry 121, Winter 2008, LA Tech Cl Cl 1-39 Chemistry 121, Winter 2008, LA Tech 1-40 Reactions of alkynes Alkynes undergo hydration, halogenation, and hydrohalogenation just like alkenes. A special application is the carbide lamp (oxidation of alkyne). 2 C (coke) + CaO (lime) + heat

---> CaC2 (calcium carbide) + CO

CaC2 + H2O ---> H-C≡C-H (acetylene) + Ca(OH)2 Acetylene serves as combustion fuel for the carbide lamp.

Chemistry 121, Winter 2008, LA Tech 1-41 Chemistry 121, Winter 2008, LA Tech 1-42

Aromatic hydrocarbons Resonance Structures of Benzene Aromatic hydrocarbons - organic compounds that had aromas and had different chemical properties from Resonance structures or contributing Benzene is the parent compound for the aromatic structures = when two or more structure can hydrocarbons. Textbook, page90. structures = when two or more structure can be drawn for a compound. Consider benzene. C6H6 In thiscase, the real structure is something between the proposed structures. Textbook, page 90-91.

Chemistry 121, Winter 2008, LA Tech 1-43 Chemistry 121, Winter 2008, LA Tech 1-44 Naming Aromatic Hydroarbons. Nomenclature Disubstituted Monosubstituted benzenes: • locate substituents by numbering or Ar-CH2CH3 • use the locators ortho (1,2-), meta (1,3-), and para (1,4-)

Ar-CH2-CH2-CH2-CH3 butylbenzene Where one group imparts a special name, name the

Ar-CH3 (methylbenzene) compound as a derivative of that molecule CH3 NH Ar-X (halobenzene) bromobenzene, X 2 COOH NO2 Ar-NO2 nitrobenzene

Ar-SO3H benzenesulfonic acid Cl Ar-NH a nitrile substituent Br 2 4-Bromotoluene 3-Chloroaniline 2-Nitrobenzoic acid (p-Bromotoluene) (m-Chloroaniline) (o-Nitrobenzoic acid)

Chemistry 121, Winter 2008, LA Tech 1-45 Chemistry 121, Winter 2008, LA Tech 1-46

Nomenclature Polysubstituted benzenes • with three or more substituents, number the atoms of the ring • if one group imparts a special name, it becomes the parent name • if no group imparts a special name, number to give the smallest set of numbers, and then list alphabetically

CH3 OH NO2 1 1 4 6 2 NO2 Br 6 2 Br 5 3 2 5 3 5 3 6 4 4 1 Br Cl Br CH2 CH3 4-Chloro-2-nitro- 2,4,6-Tribromo- 2-Bromo-1-ethyl-4- toluene phenol nitrobenzene Chemistry 121, Winter 2008, LA Tech 1-47 Chemistry 121, Winter 2008, LA Tech 1-48 Disubstituted benzenes:

Textbook, page 352. 2,6-dibromotoluene p-diethylbenzene 3,5-dinitrotoluene p-cholonitrobenzene o-nitrobenzenesulfonic acid 4-benzyl-1-octene m-cyanotoluene

Chemistry 121, Winter 2008, LA Tech 1-49 Chemistry 121, Winter 2008, LA Tech 1-50

Chemistry 121, Winter 2008, LA Tech 1-51 Chemistry 121, Winter 2008, LA Tech 1-52 Benzylic Oxidation Benzylic Oxidation Benzene is unaffected by strong oxidizing agents • if there is more than one alkyl group, each is oxidized to a -COOH group such as H2CrO4 and KMnO4 • halogen and nitro substituents are unaffected by these O O H2 Cr O 4 reagents H3 C CH3 HOC COH • an alkyl group with at least one hydrogen on the 1,4-Dimethylbenzene 1,4-Benzenedicarboxylic acid benzylic carbon is oxidized to a carboxyl group (p-xylene) (terephthalic acid)

CH 3 COOH • terephthalic acid is one of the two monomers required H2 CrO4 for the synthesis of poly(ethylene terephthalate), a O2 N Cl O2 N Cl polymer that can be fabricated into Dacron polyester 2-Chloro-4-nitrotoluene 2-Chloro-4-nitrobenzoic acid fibers and into Mylar films

Chemistry 121, Winter 2008, LA Tech 1-53 Chemistry 121, Winter 2008, LA Tech 1-54

Reactions of Benzene Reactions of Benzene The most characteristic reaction of aromatic Sulfonation:

compounds is substitution at a ring carbon HH+ 2 SO4 SO3 H + H2 O Halogenation: Benzenesulfonic acid FeCl3 HCl++2 Cl HCl Alkylation: Chlorobenzene AlCl HRX+ 3 R + HX Nitration: H2 SO4 An alkylbenzene HHNO+ 3 NO2 + H2 O Nitrobenzene Acylation: O O AlCl HR-C-X+ 3 CR + HX

An acyl An acylbenzene halide

Chemistry 121, Winter 2008, LA Tech 1-55 Chemistry 121, Winter 2008, LA Tech 1-56 Nitration Friedel-Crafts Alkylation + The electrophile is NO2 , generated in this way Friedel-Crafts alkylation forms a new C-C bond between an aromatic ring and an alkyl group H + HONO + HONOOSOH H + HSO AlCl 2 3 2 4 + Cl 3 Conjugate acid + HCl Nitric acid of nitric acid Benzene 2-Chloropropane Isopropylbenzene (Isopropyl chloride) (Cumene) H H + + HNOO 2 HO + NO2 The nitronium ion

Chemistry 121, Winter 2008, LA Tech 1-57 Chemistry 121, Winter 2008, LA Tech 1-58

Friedel-Crafts Acylations Treating an aromatic ring with an acid chloride in

the presence of AlCl3 • acid (acyl) chloride: a derivative of a carboxylic acid in which the -OH is replaced by a chlorine O

O CCH3 AlCl3 + CH3 CCl + HCl

BenzeneAcetyl ch loride Acetophenone (an acyl halide) (a ketone)

Chemistry 121, Winter 2008, LA Tech 1-59