CHAPTER 12: Unsaturated Hydrocarbons IMPORTANT COMMON NAMES: 12.1 NOMENCLATURE GEOMETRY of ALKENES. Page 12-1

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1 APTER 12: Unsaturated ydrocarbons lassify unsaturated hydrocarbons as alkenes, alkynes, or aromatics Write the IUPA names of alkenes from structural formulas Predict and describe geometric (cis-trans) isomers Describe the products of addition reactions, applying Markovnikov s rule Identify and name structural formulas for aromatic compounds ontrast the chemical properties of aromatic hydrocarbons with those of alkenes ALKENES (Olefins) & ALKYNES (Acetylenes) ALKENES: ydrocarbons that contain at least one =. General formula (monounsaturated): n 2n ALKYNES: ydrocarbons that contain at least one. General formula - (monounsaturated): n 2n 2 ydrocarbons that contain double or or triple bonds are unsaturated, they contain less than the maximum possible number of of atoms 12.1 NOMENLATURE IMPORTANT OMMON NAMES: STEP 1 STEP 2 STEP 3a STEP 3b STEP 4 Identify main (longest) carbon chain or ring that includes = Add functional group suffix (and multiplier): -ene if =, -yne if Number main-chain atoms to locate functional group. Locate functional group at lower-number atom Use multiplier prefix if 2+ functional groups Name branches and any other substituents ETYLENE (Ethene) PROPYLENE (Propene) 3 3 ISOPRENE (2-Methyl-1,3-butadiene) 12.2 GEOMETRY of ALKENES Both are 2-BUTENE ( 4 8 ) onsidering the -atoms in the longest chain: Left isomer has atoms on the same side Right isomer has atoms on opposite sides Left isomer is cis-2-butene, bp 3.7 Right isomer is trans-2-butene, bp 0.9 Page 12-1

2 For cis-trans isomerism, each atom in in the double bond must be be connected to to 2 different groups GEOMETRI ISOMERS: NOMENLATURE 3 3 l l 3 = 3 l l 3 3 STEP 1. STEP 2. Identify longest chain of -atoms with = Determine if = bond is unsymmetrical STEP 3. If unsymmetrical, use longest chain where appropriate and label as is (Z-) if the two large groups or chain segments are on the same side Trans (E-) if the two large groups or chain segments are on opposite sides 12.3 ALKENE PROPERTIES PYSIAL PROPERTIES Similar to alkanes:» Non-polar molecules» Insoluble in water» Less dense than water EMIAL PROPERTIES Major class of reaction: ADDITION eaking one bond in in the double bond and adding something to to each carbon A B + A B Properties depend on chain size + A B Unsaturated YDROGENATION = Pt Saturated Application: Alkenes have lower mp and bp than alkanes Vegetable oils contain alkene derivatives To make solid derivatives of vegetable oils: orn Oil + 2 Margarine Ni Requires heat, pressure, catalyst (Pt, Pd or Ni) Say, kids, who said chemistry isn t too groovy for words? You re a very lonely man, aren t you, Dr. Schloman? Page 12-2

3 ALOGENATION + 2 = l,, I ADDITION of + = l,, 2 O olor test for unsaturation: 2 REDDIS-BROWN OLORLESS 3 3 What you get Why: 3 MARKOVNIKOV S RULE When adds to to =, the atom bonds to to the carbon that already has the most atoms YDRATION O + 2 O ALOOL 2 O + 3O 3 AID ATALYST Biochemically important: 12.4 ADDITION POLYMERS Alkenes can be made to add to each other: OO - - OO Fumarate 2 O enzyme O OO - - OO Malate 2 2 =, 3, l, 6 5 MONOMER POLYMER monomer units Any molecule made up up of of a large number of of repeating units Page 12-3

4 12.6 AROMATI YDROARBONS Benzene and its relatives exhibit RESONANE: Formerly, hydrocarbons named for their pleasant aromas. Now: BENZENE and compounds that contain benzenelike ring structures. OO O 3 ASPIRIN O N N 2 N N N ADENINE The property where a molecule s structure can be be represented as as a combination of of 2 or or more structures with double bonds. This gives aromatic compounds chemical properties that are very different from those of alkenes NOMENLATURE Important common names: 3 TOLUENE Monosubstituted Benzenes Simple compounds are named as substituted benzene derivatives: l 2 3 hlorobenzene Ethylbenzene 3 para-ylene NO 2 3 More common names will be introduced as we discuss other functional groups. Nitrobenzene Page 12-4

5 Disubstituted Benzenes Position prefixes: l l ortho (o-) o-dichlorobenzene l Di - or Polysubstituted Benzenes Numbered ring carbons: l l l 1,2-Dichlorobenzene meta (m-) l m-dichlorobenzene 1,3-Dichlorobenzene l l l para (p-) p-dichlorobenzene 1,4-Dichlorobenzene l l BENZENE RING AS A SUBSTITUENT In some cases, the benzene ring is handled like any other substituent on a hydrocarbon backbone: 12.8 EMIAL PROPERTIES of AROMATI YDROARBONS Major reaction type is is SUBSTITUTION: replacing one or or more atoms with another atom or or functional group + A B A + B 6 5 PENYL ,4-Diphenylpentane NEEDS A ATALYST! alogenation of Benzene ompared to alkenes, benzene and its derivatives are less reactive: 2 NO REATION Oxidation of Benzene in vivo Liver enzymes catalyze formation of a reactive metabolite that has been implicated in benzeneinduced leukemogenesis: ARYL ALIDE 2 Fe 3 + Benzene rings have extra chemical stability due to to resonance. liver, marrow enzymes [O] O reacts with DNA, RNA, proteins O Page 12-5