Chemistry 121(01) Winter 2010-11 Introduction to Organic Chemistry and Biochemistry Instructor Dr. Upali Siriwardane (Ph.D. Ohio State) E-mail: upali@chem.latech.edu Office: 311 Carson Taylor all ; Phone: 318-257-4941; Office ours: MWF 8:00 am - 10:00 am; TT 9:00 10:00 am & 1:00-2:00 pm. December 17, 2010 Test 1 (Chapters 12-13) January 19, 2011 Test 2 (Chapters 14,15 & 16) February 7, 2011 Test 3(Chapters 17, 18 & 19) February 23, 2011 Test 4 (Chapters 20, 21 & 22) February 24, 2011 Comprehensive Make Up Exam: Chapter 13: Unsaturated ydrocarbons Sections 4.1-4.5 13-1 13-2 Chapter 13: Unsaturated ydrocarbons 13.2 Characteristics of Alkenes and Cycloalkenes 13.3 Names for Alkenes and Cycloalkenes 13.4 Line-Angle Formulas for Alkenes 13.5 Isomerism in Alkenes 13.6 Naturally Occurring Alkenes 13.7 Physical Properties of Alkenes 13.8 Chemical Reactions of Alkenes 13.9 Polymerization of Alkenes: Addition Polymers 13.10 Alkynes 13.11 Aromatic ydrocarbons 13.12 Names for Aromatic ydrocarbons 13.13 Aromatic ydrocarbons: Physical Properties and Sources 13.14 Chemical Reactions of Aromatic ydrocarbons 13.15 Fused-Ring Aromatic Compounds Chemical Connections: Ethene: A Plant ormone and igh-volume Industrial Chemical; Cis-Trans Isomerism and Vision; Carotenoids: A Source of Color; Fused-Ring Aromatic ydrocarbons and Cancer IUPAC Nomenclature of Alkyne CAG 13.2 13-3 13-4 1
Unsaturated ydrocarbons cont d Fig. 13.18 2-chlorotoluene molecule Unsaturated hydrocabons ydrocarbons with carbon-carbon double bonds and triple bonds double bonds: alkenes triple bonds: alkynes three alternating double bond in 6 carbon ring: aromatics Copyright oughton Mifflin Company. All rights reserved. 13 5 13-5 13-6 Unsaturated ydrocarbons in Use Beta-carotene is in carrots Acetylene: Welding Unsaturated ydrocarbons: Alkenes Alkynes Arenes C C C C C C Ethene is the hormone that causes tomatoes to ripen. sex pheromones in insect control involves luring insect into a trap. ethene ethyne benzene C 2 4 C 2 2 C 6 6 C n 2n C n 2n-2 C n n unsaturated unsaturated Aromatic alkene alkyne Arene Chapters 13 Chapters 13 Chapter 13 13-7 13-8 2
Units of Unsaturation Compounds that have have fewer hydrogens than saturated hydrocarbons (C n 2n+2 ). Two hydrogen are considered as unit of unstauration Cycloalkane ring C n 2n (one unit of unsat.) Structure of Alkenes Alkene: contains a carbon-carbon double bond and has the general formula C n 2n The two carbon atoms of a double bond and the four atoms bonded to them lie in a plane, with bond angles of approximately 120 Unsaturated hydrocarbons: bond C n 2n (one unit of unsat.) bond C n 2n-2 (two units of unsat.) 121.7 C C Ethylene 124.7 C 3 C C Propene 13-9 13-10 Bonding in ethene (ethylene) Fig. 13.1 In ethene, the atoms are in a flat rather than a tetrahedral arrangement. Planar Structure of Alkenes According to the orbital overlap model, a double bond consists of a s bond formed by overlap of sp 2 hybrid orbitals a p bond formed by overlap of parallel 2p orbital Rotating by 90 breaks the pi bond 13-11 13-12 3
Structure of Alkynes The functional group of an alkyne is a carbon-carbon triple bond A triple bond consists of one s bond formed by the overlap of sp hybrid orbitals two p bonds formed by the overlap of sets of parallel 2p orbitals Alkenes Second members of the hydrocarbon family. contain only hydrogen and carbon have single bonds and at least one C=C double bond All members have the general formula of C n 2n Twice as many hydrogen as carbon 13-13 13-14 Alkenes: Naming and Structures One simple class of compound is the alkene which has only C, and single bonds. ethene propene 2- butene C 2 4 C 3 6 C 4 8 C 2 C 2 C 3 C 2 C 2 C 3 C 2 CC 3 13-15 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. use the infix -en- to show the presence of a carbon-carbon double bond use the infix -yn- to show the presence of a carbon-carbon triple bond 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 cycloalkene, the double bond must be numbered 1,2 13-16 4
IUPAC Nomenclature of Alkynes use the infix -yn- to show the presence of a carboncarbon triple bond number the parent chain to give the 1st carbon of the triple bond the lower number follow IUPAC rules for numbering and naming substituents 1 1 2 2 3 4 4 5 3 6 7 3-Methyl-1-butyne 6,6-Dimethyl-3-heptyne Example of IUPAC Nomenclature of Alkenes Cycloalkanes 5 3 1 6 4 2 6 4 2 4 2 5 3 1 5 3 1 1-exene 5 4 3 1 2 4-Methyl-1-hexene C 3 3 4 2 5 1 6 3-Methylcyclopentene 1,6-Dimethylcyclohexene 2-Ethyl-3-methyl- 1-pentene C 3 C 3 13-17 13-18 Nomenclature of Alkenes: Common Names Alkenes Some alkenes, particularly low-molecular-weight ones, are known almost exclusively by their common names C 3 First four members of the alkanes Name # of C Condensed formula IUPAC: Common: C 2 =C 2 C 3 C=C 2 C 3 C=C 2 Ethene Propene 2-Methylpropene Ethylene Propylene Isobutylene Ethene 2 C 2 =C 2 Propene 3 C 3 C=C 2 2-Butene 4 C 3 C=CC 3 Called a homologous series Members differ by number of C 2 groups 13-19 13-20 5
Physical State of Alkynes Physical state summary for unbranched 1 alkynes at room temperature and pressure. Cis and trans Geometrical isomers of alkenes two groups are said to be located cis to each other if they lie on the same side of a plane with respect to the double bond. If they are on opposite sides, their relative position is described as trans. 13-21 13-22 Isomerism in Alkanes & Alkenes Cis-trans isomerism in 2-butene Fig. 13.3 Cis-trans isomers: Different representatives of the cis and trans isomers of 2-butene. Fig. 13.2 A comparison of structural isomerism possibilities for four and five-carbon alkane and alkene systems. 13-23 13-24 6
Unsaturated Aromatic ydrocarbons Geometrical Stereoisomerism Because of restricted rotation about a C-C double bond, groups on adjacent carbons are either cis or trans to each other CC 13.2 3 C C C C 3 cis-2-butene mp -139 C, bp 4 C 3 C C C C 3 t rans-2-butene mp -106 C, bp 1 C 13-25 13-26 Physical Properties Alkenes and alkynes are nonpolar compounds the only attractive forces between their molecules are dispersion forces Their physical properties are similar to those of alkanes of similar carbon skeletons those that are liquid at room temperature are less dense than water (1.0 g/m L) they dissolve in each other and in nonpolar organic solvents they are insoluble in water Cis-Trans Isomerism trans alkenes are more stable than cis alkenes because of nonbonded interaction strain between alkyl substituents of the same side of the double bond 13-27 13-28 7
Summary of Physical State of Unsaturated ydrocarbons Geometric isomers There are two possible arrangements. Example 2-butene 3C C3 3C C=C C=C C3 cis Largest groups are on the same side. trans Largest groups are on opposite sides. 13-29 13-30 Cis-Trans Isomerism in Cycloalkenes the configuration of the double bond in cyclopropene through cycloheptene must be cis; these rings are not large enough to accommodate a trans double bond C 3 C 3 cyclooctene is the smallest cycloalkene that can accommodate a trans double bond Cis-Trans Isomerism Dienes, trienes, and polyenes for an alkene with n carbon-carbon double bonds, each of which can show cis-trans isomerism, 2 n cis-trans isomers are possible consider 2,4-heptadiene; it has four cis-trans isomers, two of which are drawn here Double bond C 2 -C 3 C 4 -C 5 trans trans trans cis cis trans cis cis 2 2 4 4 t rans,t rans-2,4- heptadiene trans,cis-2,4- heptadiene trans- Cyclooctene cis-cyclooctene 13-31 13-32 8
Naturally Occurring AlkenesCis-Trans Isomerism vitamin A has five double bonds four of the five can show cis-trans isomerism vitamin A is the all-trans isomer O enzymecatalyzed oxidation Naturally Occurring Alkenes: The Terpenes Terpene: a compound whose carbon skeleton can be divided into two or more units identical with the carbon skeleton of isoprene Vitamin A (retinol) O head 1 2 3 4 tail Vitamin A aldehyde (retinal) 2-Methyl-1,3-butadiene (Isoprene) 13-33 13-34 Terpenes with isoprene units Terpenes: Polymers of Isoprene myrcene, C 10 16, a component of bayberry wax and oils of bay and verbena menthol, from peppermint O 13-35 13-36 9
Terpenes Vitamin A (retinol) the four isoprene units in vitamin A are shown in red they are linked head to tail, and cross linked at one point (the blue bond) to give the six-membered ring Reactions of Unsaturated ydrocarbons CAG 13.1 O 13-37 13-38 Reactions of alkenes Combustion C 2 4 + 4 O 2 2 CO 2 + 2 2 O + heat Addition Reactions The exposed electrons of double bonds make alkenes more reactive than alkanes and show addition reactions. Alkynes also under go combustion reactions similarly 13-39 13-40 10
Addition Reaction of Alkenes In an alkene addition, reaction, the atoms provided by an incoming molecule are attached to the carbon atoms originally joined by a double bond. In the process, the double bond becomes a single bond. Addition of Bromines Fig. 13.9 A bromine in water solution is reddish brown. When a small amount of such a solution is added to an unsaturated hydrocarbon, the added solution is decolorized. 13-41 13-42 Markovnikov s Rule Vladimir Markovnikov synthesized rings containing four carbon atoms and seven carbon atoms. Markovnikov Rule Non symmetric alkene In hydrohalogenation and hydration reations hydrogen adds to the double-bonded carbon with the most hydrogens 13-43 13-44 11
Addition Polymerizations Preparation of polystyrene. Polymers of Unsaturated ydrocarbons (a) polyethylene (b) polypropylene (c) poly (vinyl chloride) 13-45 13-46 alogenation alogenation - Addition of halogen to the double bond. Textbook page xx. 13-47 13-48 12
ydrogenation Addition of hydrogen to the double bond. Textbook page 84 13-49 13-50 ydration Addition of water to the double bond. Textbook page86. 13-51 13-52 13
Polymerization Formula Name Monomer Polymer Polypropylene C 3 C=C 2 ( C-C 2 ) C 3 Polystyrene -C=C 2 ( C-C 2 ) Polychloroprene 2 C=CC=C 2 ( C 2 C=CC 2 ) 13-53 Cl Cl 13-54 13-55 13-56 14
Naming alkenes and alkynes Find the longest carbon chain. Use as base name with an ene or yne ending. Number the chain to give lowest number for the carbons of the double or triple bond. Locate any branches on chain. Use base names with a yl ending. 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.. Alkyne Bonding Ethyne, is the simplest alkyne. 13-57 13-58 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 ---> CaC 2 (calcium carbide) + CO CaC 2 + 2 O ---> -C C- (acetylene) + Ca(O) 2 Acetylene serves as combustion fuel for the carbide lamp. Aromatic hydrocarbons Aromatic hydrocarbons - organic compounds that had aromas and had different chemical properties from alkane Benzene is the parent compound for the aromatic hydrocarbons. Textbook, page90. Consider benzene. C 6 6 13-59 13-60 15
Unsaturated ydrocarbons cont d Unsaturated ydrocarbons cont d Fig. 13.17 Space-filling and ball-and-stick models for the structure of benzene. CC 13. 4 Copyright oughton Mifflin Company. All rights reserved. 13 61 13-61 13-62 Resonance Structures of Benzene Resonance structures or contributing structures = when two or more structure can be drawn for a compound. In thiscase, the real structure is something between the proposed structures. Textbook, page 90-91. Naming Aromatic ydroarbons. Monosubstituted benzenes: Ar-C 2 C 3 ethylbenzene Ar-C 2 -C 2 -C 2 -C 3 butylbenzene Ar-C 3 (methylbenzene) toluene Ar-X (halobenzene) bromobenzene, Ar-NO 2 nitrobenzene Ar-SO 3 benzenesulfonic acid Ar-N 2 a nitrile substituent X 13-63 13-64 16
Nomenclature Disubstituted benzenes locate substituents by numbering or use the locators ortho (1,2-), meta (1,3-), and para (1,4-) Where one group imparts a special name, name the compound as a derivative of that molecule C 3 Br 4-Bromotoluene (p-bromotoluene) N 2 Cl 3-Chloroaniline (m-chloroaniline) COO NO 2 2-Nitrobenzoic acid (o-nitrobenzoic acid) 13-65 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 C 3 6 1 2 NO 2 O Br 6 1 2 Br 5 NO 2 4 3 5 3 4 Cl 4-Chloro-2-nitrotoluene 5 3 4 Br 2,4,6-Tribromophenol 6 2 1 Br C 2 C 3 2-Bromo-1-ethyl-4- nitrobenzene 13-66 Disubstituted benzenes: Textbook, page 352. 2,6-dibromotoluene p-diethylbenzene 3,5-dinitrotoluene p-cholonitrobenzene o-nitrobenzenesulfonic acid 4-benzyl-1-octene m-cyanotoluene 13-67 13-68 17
Reactions of Benzene The most characteristic reaction of aromatic compounds is substitution at a ring carbon alogenation: FeCl + Cl 3 2 Cl + Cl Chlorobenzene Nitration: 2 SO 4 + NO 3 NO 2 + 2 O Nitrobenzene 13-69 13-70 13-71 13-72 18
Benzylic Oxidation Benzene is unaffected by strong oxidizing agents such as 2 CrO 4 and KMnO 4 halogen and nitro substituents are unaffected by these reagents an alkyl group with at least one hydrogen on the benzylic carbon is oxidized to a carboxyl group C 3 2 CrO 4 COO O 2 N Cl O 2 N Cl 2-Chloro-4-nitrotoluene 2-Chloro-4-nitrobenzoic acid Benzylic Oxidation if there is more than one alkyl group, each is oxidized to a -COO group 3 C C 3 1,4-Dimethylbenzene (p-xylene) 2 CrO 4 O OC O CO 1,4-Benzenedicarboxylic acid (terephthalic acid) terephthalic acid is one of the two monomers required for the synthesis of poly(ethylene terephthalate), a polymer that can be fabricated into Dacron polyester fibers and into Mylar films 13-73 13-74 Reactions of Benzene Sulfonation: Alkylation: + 2 SO 4 SO 3 + 2 O Acylation: + RX + O R-C-X An acyl halide Benzenesulfonic acid AlCl 3 R + X An alkylbenzene AlCl 3 O CR An acylbenzene + X 13-75 Nitration The electrophile is NO 2+, generated in this way O NO 2 + O SO 3 + O NO 2 + SO 4 Nitric acid Conjugate acid of nitric acid + O NO 2 O + + NO 2 The nitronium ion 13-76 19
Friedel-Crafts Alkylation Friedel-Crafts alkylation forms a new C-C bond between an aromatic ring and an alkyl group + Cl AlCl 3 Benzene 2-Chloropropane (Isopropyl chloride) Isopropylbenzene (Cumene) + Cl Friedel-Crafts Acylations Treating an aromatic ring with an acid chloride in the presence of AlCl 3 acid (acyl) chloride: a derivative of a carboxylic acid in which the -O is replaced by a chlorine + O C 3 CCl O CC 3 AlCl 3 + Cl Benzene Acetyl chloride (an acyl halide) Acetophenone (a ketone) 13-77 13-78 20