Organic Chemistry, Fourth Edition, Chapter 8 - Addition Reactions of Alkenes PDF

Organic Chemistry Fourth Edition Chapter 8 Addition Reactions of Alkenes This deck contains equations authored in Math Type. For the full experience, please download the Math Type software plug-...

Organic Chemistry Fourth Edition Chapter 8 Addition Reactions of Alkenes This deck contains equations authored in Math Type. For the full experience, please download the Math Type software plug-in. Copyright ©2021 John Wiley & Sons, Inc. Ozlem Dilek 8.1 Introduction to Addition Reactions / Common Types Addition is C=C π bond is the opposite converted to two new of elimination sigma bonds Table 8.1 some common types of addition reactions Copyright ©2021 John Wiley & Sons, Inc. 2 8.1 Introduction to Addition Reactions / Description The π bond is an electron-pair donor Copyright ©2021 John Wiley & Sons, Inc. 3 8.2 Alkenes in Nature and Industry / Acyclic Naturally occurring, acyclic alkenes: Copyright ©2021 John Wiley & Sons, Inc. 4 8.2 Alkenes in Nature and Industry / Cyclic Cyclic and polycyclic alkenes: Copyright ©2021 John Wiley & Sons, Inc. 5 8.2 Alkenes in Nature and Industry / Pheromones C=C double bonds often found in the structures of pheromones Copyright ©2021 John Wiley & Sons, Inc. 6 8.2 Alkenes in Nature and Industry / Precursors Alkenes are critical precursors in the chemical industry Each year, over 70 billion pounds of propylene (propene) and 200 billion pounds of ethylene (ethene) are made from cracking petroleum Copyright ©2021 John Wiley & Sons, Inc. 7 8.2 Alkenes in Nature and Industry / Petroleum Products Copyright ©2021 John Wiley & Sons, Inc. 8 8.3 Alkene Nomenclature / Steps Alkenes are given IUPAC names using the same procedure to name alkanes, with minor modifications 1. Identify the parent chain, which includes the C=C double bond. 2. Identify and name the substituents. 3. Assign a locant (and prefix if necessary) to each substituent. Give the C=C double bond the lowest number possible. 4. List the numbered substituents before the parent name in alphabetical order. Ignore prefixes (except iso) when ordering alphabetically. 5. The C=C double bond locant is placed either just before the parent name or just before the -ene suffix. Copyright ©2021 John Wiley & Sons, Inc. 9 8.3 Alkene Nomenclature / Step One Identify the parent chain, which must include the C=C double bond. o The name of the parent chain ends in -ene rather than -ane. o The parent chain must include the C=C double bond. Copyright ©2021 John Wiley & Sons, Inc. 10 8.3 Alkene Nomenclature / Steps Two and Three 2. Identify and name the substituents. 3. Assign a locant (and prefix if necessary) to each substituent. Give the C=C double bond the lowest number possible. o The locant of the double bond is a single number, and is the number indicating where the double bond starts. The alkene above is located at the “2” carbon. Copyright ©2021 John Wiley & Sons, Inc. 11 8.3 Alkene Nomenclature / Steps Four and Five 4. List the numbered substituents before the parent name in alphabetical order. Ignore prefixes (except iso) when ordering alphabetically. 5. The C=C double bond locant is placed either just before the parent name or just before the -ene suffix. Note: This alkene has the E configuration, which must be indicated in the name, in parentheses: (E)-5,5,6-trimethylhept-2-ene. Copyright ©2021 John Wiley & Sons, Inc. 12 8.4 Addition vs. Elimination / Overview Addition and elimination are equilibrating reactions: o Which side is favored depends on temperature o The higher the temperature, the more important entropy becomes: Higher temperature means a bigger entropy term Copyright ©2021 John Wiley & Sons, Inc. 13 8.4 Addition vs. Elimination / Enthalpy Addition reactions are favored by enthalpy. Sigma (σ) bonds are stronger (more stable) than pi (π) bonds ∆H = Bond broken − bonds formed ∆H = 166 kcal/mol − 185 kcal/mol ∆H = −19 kcal/mol Copyright ©2021 John Wiley & Sons, Inc. 14 8.4 Addition vs. Elimination / Entropy Addition reactions are not favored by entropy. Two molecules combine to form one product; entropy decreases Two reactants One product Copyright ©2021 John Wiley & Sons, Inc. 15 8.4 Addition vs. Elimination / Enthalpy vs Entropy At lower temperatures, enthalpy dominates, and addition reactions are favored At higher temperatures, entropy dominates, and elimination reactions are favored Therefore, lower temperatures are typically used when doing an addition reaction Copyright ©2021 John Wiley & Sons, Inc. 16 8.5 Hydrohalogenation Hydrohalogenation: addition of H-X to an alkene can use HCl, HBr, or HI If the alkene is not symmetrical, then two regioisomers are possible, depending on which carbon gets the “H” and the “X” Copyright ©2021 John Wiley & Sons, Inc. 17 8.5 Hydrohalogenation – Regioselectivity / Adding HX Hydrohalogenation is regioselective for Markovnikov addition In 1869, Markovnikov observed the H atoms tend to add to the carbon already bearing more H atoms The halogen is generally installed at the more substituted carbon Copyright ©2021 John Wiley & Sons, Inc. 18 8.5 Hydrohalogenation – Regioselectivity / Adding HX in ROOR When peroxides are used with HBr, the opposite regioselectivity is observed. The reaction mechanism must be different, when peroxides are present. Copyright ©2021 John Wiley & Sons, Inc. 19 8.5 Hydrohalogenation – Regioselectivity / Modulating HX Addition The important lesson here is that the regioselectivity of HBr addition can be controlled: Copyright ©2021 John Wiley & Sons, Inc. 20 8.5 Hydrohalogenation – Regioselectivity / Practice CONCEPTUAL CHECKPOINT – Draw the expected major product for the following reactions Copyright ©2021 John Wiley & Sons, Inc. 21 8.5 Hydrohalogenation – Regioselectivity / Practice Answers CONCEPTUAL CHECKPOINT – Draw the expected major product for the following reactions For more practice problems, see Conc. Checkpoint 8.5 (Draw the Product), 8.6 (Identify the Reagents) Copyright ©2021 John Wiley & Sons, Inc. 22 8.5 Hydrohalogenation – Mechanism / Overview The mechanism is a two-step process Copyright ©2021 John Wiley & Sons, Inc. 23 8.5 Hydrohalogenation – Mechanism / Graphical Interpretation The step with the highest Ea is the rate determining step, which is the formation of the carbocation intermediate (the first step) Copyright ©2021 John Wiley & Sons, Inc. 24 8.5 Hydrohalogenation – Mechanism / Two Pathways Recall that there are two possible products, Markovnikov and anti-Markovnikov Anti- Markovnikov pathway Markovnikov pathway Markovnikov product is formed because of carbocation stability Copyright ©2021 John Wiley & Sons, Inc. 25 8.5 Hydrohalogenation – Mechanism / Forming the Markovnikov Product The Markovnikov product is formed through a lower energy transition state (therefore, a faster reaction). Practice with SkillBuilder 8.1 – Drawing a Mechanism (HX) Copyright ©2021 John Wiley & Sons, Inc. 26 8.5 Hydrohalogenation – Stereochemistry / Overview Hydrohalogenation may result in the formation of a chiral center There are actually two Markovnikov products formed in this rxn Two enantiomers are formed in equal amounts Copyright ©2021 John Wiley & Sons, Inc. 27 8.5 Hydrohalogenation – Stereochemistry / Intermediate The carbocation intermediate can be attacked from either side of the empty p orbital, with equal probability Practice with CONCEPTUAL CHECKPOINT 8.9 – Predict the Products Copyright ©2021 John Wiley & Sons, Inc. 28 8.5 Hydrohalogenation – Rearrangements / Overview Recall carbocations can rearrange (hydride or methyl shift) if they can become more stable. When this alkene undergoes hydrohalogenation, the 2° carbocation could rearrange to a more stable 3° carbocation. Copyright ©2021 John Wiley & Sons, Inc. 29 8.5 Hydrohalogenation – Rearrangements / Common Outcome Recall carbocations can rearrange (hydride or methyl shift) if they can become more stable. When carbocation rearrangements can occur, they DO occur. Practice with SkillBuilder 8.2 – Drawing a Mechanism Copyright ©2021 John Wiley & Sons, Inc. 30 8.6 Acid-Catalyzed Hydration / Overview The components of water (H and OH) are added across the π bond Acid-catalyzed hydration follows Markovnikov regioselectivity Sulfuric acid is a commonly used acid catalyst Copyright ©2021 John Wiley & Sons, Inc. 31 8.6 Acid-Catalyzed Hydration / More Substituted Carbon The OH is added to the more substituted carbon of the alkene The more substituted the carbon atom is, the faster the reaction This data is consistent with a mechanism that proceeds through a carbocation intermediate Copyright ©2021 John Wiley & Sons, Inc. 32 8.6 Hydration – Mechanism / Beginning is Familiar The mechanism for acid-catalyzed hydration begins the same as hydrohalogenation: Copyright ©2021 John Wiley & Sons, Inc. 33 8.6 Hydration – Mechanism / Additional Final Step The mechanism for acid-catalyzed hydration begins the same as hydrohalogenation: But with hydration, nucleophilic attack produces an oxonium ion, which is deprotonated to afford the alcohol product: Copyright ©2021 John Wiley & Sons, Inc. 34 8.6 Hydration – Thermodynamics The reactants and products of hydration are in equilibrium We exploit Le Chatelier’s principle to control the equilibrium If we are synthesizing an alcohol from an alkene, we would use excess water If we are synthesizing an alkene from an alcohol, we would use concentrated acid, and not add water to the reaction Copyright ©2021 John Wiley & Sons, Inc. 35 8.6 Hydration – Stereochemistry The stereochemistry of hydration is analogous to hydration, for the same reasons. If a new chiral center is formed, a mixture of R and S is obtained As always, if a chiral center is formed in a reaction, then a racemic mixture is obtained. Practice with SkillBuilder 8.3 – Drawing a Mechanism Copyright ©2021 John Wiley & Sons, Inc. 36 8.7 Oxymercuration-Demercuration / Overview Markovnikov hydration (H2O, H2SO4) has limited application… rearrangements often occur, giving mixture of products Oxymercuration-demercuration is an alternative o Markovnikov addition of H and OH o No rearrangements occur Copyright ©2021 John Wiley & Sons, Inc. 37 8.7 Oxymercuration-Demercuration / Lewis Acid The mercuric cation is the (Lewis) acid in this reaction, instead of H+ Copyright ©2021 John Wiley & Sons, Inc. 38 8.7 Oxymercuration-Demercuration / No Rearrangements When the p bond attacks the mercuric cation, a stabilized cation is formed, and so it will not rearrange like carbocations do. Copyright ©2021 John Wiley & Sons, Inc. 39 8.7 Oxymercuration-Demercuration / Nucleophilic Attack The mercurinium ion is an electrophile, and it can easily be attacked by a nucleophile NaBH4 is generally used to replace the —HgOAc group with a —H group via a free radical mechanism Copyright ©2021 John Wiley & Sons, Inc. 40 8.6 Oxymercuration-Demercuration / Comparison with Hydration The two-reaction sequence provides same product as acid-catalyzed hydration, but without rearrangement. Practice with CONCEPTUAL CHECKPOINT 8.16, 8.17 – Predict the Products Copyright ©2021 John Wiley & Sons, Inc. 41 8.8 Hydroboration-Oxidation / Overview Hydroboration-Oxidation adds H and OH with anti-Markovnikov regioselectivity Note that this is a two-reaction sequence Copyright ©2021 John Wiley & Sons, Inc. 42 8.8 Hydroboration-Oxidation / Stereoselective Hydroboration-Oxidation is also stereoselective o H and OH are added in a syn fashion Anti addition is NOT observed Copyright ©2021 John Wiley & Sons, Inc. 43 8.8 Hydroboration-Oxidation / MO Viewpoint Geometry/hybridization of BH3 is analogous to a carbocation Copyright ©2021 John Wiley & Sons, Inc. 44 8.8 Hydroboration-Oxidation / Filling Boron’s Valence Shell The boron atom does not have an octet. BH3 forms a dimer to help fulfill the boron atoms’ octets. The resonance hybrid reveals three-center, two-electron bonds: Copyright ©2021 John Wiley & Sons, Inc. 45 8.8 Hydroboration-Oxidation / Ether Solvent B2H6 can be stabilized by using an ether solvent so that an appreciable amount of BH3 is present The active reagent is BH3˙THF Copyright ©2021 John Wiley & Sons, Inc. 46 8.8 Hydroboration-Oxidation Mechanism / Regioselectivity Hydroboration follows anti-Markovnikov regioselectivity The less-substituted carbon attacks the boron, and the more-substituted carbon develops a δ+ which triggers a hydride shift Recall that the more-substituted carbon will be better at stabilizing a partial positive charge Copyright ©2021 John Wiley & Sons, Inc. 47 8.8 Hydroboration-Oxidation / Three Alkene Equivalents per Borane Hydroboration follows anti-Markovnikov regioselectivity One BH3 reacts with three equivalents of alkene Copyright ©2021 John Wiley & Sons, Inc. 48 8.8 Hydroboration-Oxidation Mechanism / Sterics Hydroboration follows anti-Markovnikov regioselectivity Sterics also influence the regioselectivity Copyright ©2021 John Wiley & Sons, Inc. 49 8.8 Hydroboration-Oxidation Mechanism / Summary Copyright ©2021 John Wiley & Sons, Inc. 50 8.8 Hydroboration-Oxidation Stereoselectivity / Syn Addition Hydroboration is stereospecific: only syn addition occurs If only one chiral center is formed, a pair of enantiomers is formed by addition to either face of the alkene Copyright ©2021 John Wiley & Sons, Inc. 51 8.8 Hydroboration-Oxidation / Enantiomers Hydroboration is stereospecific: only syn addition occurs If two chiral centers are formed, a pair of enantiomers is obtained Copyright ©2021 John Wiley & Sons, Inc. 52 8.8 Hydroboration-Oxidation / Practice Predict the product(s) of the following reaction: Copyright ©2021 John Wiley & Sons, Inc. 53 8.8 Hydroboration-Oxidation / Practice Answer Predict the product(s) of the following reaction: Two chiral centers are formed. Why do we not obtain a mixture of enantiomers? Practice with SkillBuilder 8.4 – Predict the Products Copyright ©2021 John Wiley & Sons, Inc. 54 8.9 Catalytic Hydrogenation / Overview Hydrogenation – the addition of H2 across a C=C double bond Requires a metal catalyst An alkene is reduced to the corresponding alkane Copyright ©2021 John Wiley & Sons, Inc. 55 8.9 Catalytic Hydrogenation Stereoselectivity / Syn Addition Hydrogenation – the addition of H2 across a C=C double bond Stereospecific – only syn addition is observed Two chiral centers are formed only the stereoisomers resulting from syn addition are obtained Copyright ©2021 John Wiley & Sons, Inc. 56 8.9 Catalytic Hydrogenation / Graphical Interpretation Without the metal catalyst, the addition of H2 is too slow due to a very high activation energy (Ea) Copyright ©2021 John Wiley & Sons, Inc. 57 8.9 Catalytic Hydrogenation / Metal Surface The metal surface binds the H2 and the alkene, which explains why both H atoms are added to the same face of the alkene (syn addition) Copyright ©2021 John Wiley & Sons, Inc. 58 8.9 Catalytic Hydrogenation / Symmetrical Alkenes Syn addition of H2 to a symmetrical alkene will not produce a pair of enantiomers. A meso compound will be produced instead. Practice with SkillBuilder 8.5 – Predict the Products (H2) Copyright ©2021 John Wiley & Sons, Inc. 59 8.9 Catalytic Hydrogenation / Types of Catalyst Heterogeneous catalyst – does not dissolve in reaction medium, like Pt or Pd metal Homogeneous catalyst – does dissolve in the reaction medium, accomplished by using ligands with the metal Copyright ©2021 John Wiley & Sons, Inc. 60 8.9 Asymmetric Hydrogenation / Background Recall that the creation of one or two chiral centers results in a mixture of enantiomers (unless a meso compound is produced) Copyright ©2021 John Wiley & Sons, Inc. 61 8.9 Asymmetric Hydrogenation / Chiral Catalyst If a chiral catalyst is used, it is possible to synthesize only one enantiomer as the major product This can be accomplished by replaced the phosphine ligands on the Wilkinson catalyst with chiral phosphine ligands Copyright ©2021 John Wiley & Sons, Inc. 62 8.9 Asymmetric Hydrogenation / Knowles If a chiral catalyst is used, it is possible to synthesize only one enantiomer as the major product William S. Knowles developed a synthesis of L-dopa using an asymmetric hydrogenation as the key step He later shared the Nobel Prize in Chemistry in 2001 Copyright ©2021 John Wiley & Sons, Inc. 63 8.9 Asymmetric Hydrogenation / Noyori If a chiral catalyst is used, it is possible to synthesize only one enantiomer as the major product Ryoji Noyori showed that the chiral ligand BINAP also affords one enantiomer with high selectivity For his work, Noyori also shared the Nobel Prize in Chemistry (with Knowles) in 2001 Copyright ©2021 John Wiley & Sons, Inc. 64 8.10 Halogenation / Overview Halogenation – addition of two halogen atoms across a C=C double bond This is a key step in the production of polyvinylchloride (PVC) Copyright ©2021 John Wiley & Sons, Inc. 65 8.10 Halogenation / Anti Addition Halogenation only practical with Cl2 and Br2 Halogenation with I2 is poor; halogenation with F2 is too violent Stereoselectivity – halogenation occurs with anti addition Copyright ©2021 John Wiley & Sons, Inc. 66 8.10 Halogenation / Bromine Br2 is nonpolar, but polarizable. Approach of a nucleophile will induce a dipole Think of Br2 as a bromine atom bonded to a good leaving group The alkene acts as the nucleophile Copyright ©2021 John Wiley & Sons, Inc. 67 8.10 Halogenation – Mechanism / No Syn Addition Only anti addition is observed, so the mechanism is not consistent with a true carbocation intermediate Syn addition doesn’t occur Copyright ©2021 John Wiley & Sons, Inc. 68 8.10 Halogenation – Mechanism / Anti Addition The formation of a bromonium ion intermediate is consistent with anti addition This intermediate is similar to the mercurinium ion Copyright ©2021 John Wiley & Sons, Inc. 69 8.10 Halogenation – Mechanism / Final Step The formation of a bromonium ion intermediate is consistent with anti addition Br– attacks the bromonium ion in an SN2 process (gives anti addition) Copyright ©2021 John Wiley & Sons, Inc. 70 8.10 Halogenation – Stereoselectivity Halogenation is stereospecific, the stereochemistry of the starting alkene determines the stereochemistry of the product(s) Practice with CONCEPTUAL CHECKPOINT 8.24 – Predict the Product Copyright ©2021 John Wiley & Sons, Inc. 71 8.10 Halohydrin Formation / Overview Halohydrins – formed when halogenation is conducted in water Water acts as the nucleophile that attacks the bromonium ion There are many more H2O molecules compared to Br– ions, so attack of the bromonium ion by H2O is more likely than Br– Copyright ©2021 John Wiley & Sons, Inc. 72 8.10 Halohydrin Formation / Bromohydrin and Chlorohydrin After water attacks, it is deprotonated to yield the neutral bromohydrin product Here, the product is called a chlorohydrin Copyright ©2021 John Wiley & Sons, Inc. 73 8.10 Halohydrin Formation – Regioselectivity / Halide vs OH addition Halohydrin Formation is regioselective o The halide adds to the less-substituted carbon o The OH adds to the more-substituted carbon Copyright ©2021 John Wiley & Sons, Inc. 74 8.10 Halohydrin Formation – Regioselectivity / Origin Regioselectivity results from H2O attacking the more- substituted carbon (faster than it attacks the less substituted one). Copyright ©2021 John Wiley & Sons, Inc. 75 8.10 Halohydrin Formation – Regioselectivity / Cationic Character Regioselectivity results from H2O attacking the more- substituted carbon (faster than it attacks the less-substituted one). The more-substituted carbon has more cationic character. Practice with SkillBuilder 8.6 – Predict Products (Halohydrin) Copyright ©2021 John Wiley & Sons, Inc. 76 8.11 Anti Dihydroxylation / Overview Dihydroxylation – addition of OH and OH across the π bond Anti dihydroxylation of an alkene is a two-step procedure Copyright ©2021 John Wiley & Sons, Inc. 77 8.11 Anti Dihydroxylation / Step One 1. Conversion of alkene to an epoxide: A peroxyacid is used as the reagent (RCO3H) Copyright ©2021 John Wiley & Sons, Inc. 78 8.11 Anti Dihydroxylation – Mechanism / Step Two 1. Conversion of alkene to an epoxide: 2. The epoxide is reacted with H2O and acid catalyst to form the anti diol. Copyright ©2021 John Wiley & Sons, Inc. 79 8.11 Anti Dihydroxylation / Similar Intermediates Note the similarities between these three key intermediates Ring strain and a +1 formal charge makes these structures good electrophiles All three yield anti products, because the nucleophile must attack from the side opposite the leaving group (SN2-like process) Practice with SkillBuilder 8.7 – Predict the Products Copyright ©2021 John Wiley & Sons, Inc. 80 8.12 Syn Dihydroxylation / Overview Syn Dihydroxylation – adds OH and OH across the π bond, in a concerted, syn fashion. Copyright ©2021 John Wiley & Sons, Inc. 81 8.12 Syn Dihydroxylation / Importance of NMO OsO4 is expensive and toxic. NMO or an alkyl peroxide is used as an co-oxidant, so only a catalytic amount of OsO4 is necessary. Copyright ©2021 John Wiley & Sons, Inc. 82 8.12 Syn Dihydroxylation / Potassium Permanganate Has Limited Use Syn dihydroxylation can also be achieved with KMnO4 but only under mild conditions (cold temperatures) The synthetic utility of KMnO4 is limited, because it reacts with many other functional groups as well Practice with CONCEPTUAL CHECKPOINT 8.31 – Predict the Product Copyright ©2021 John Wiley & Sons, Inc. 83 8.13 Oxidative Cleavage / Overview C=C double bonds are also reactive toward oxidative cleavage Ozonolysis is one such process Ozone exists as a resonance hybrid of two contributors Copyright ©2021 John Wiley & Sons, Inc. 84 8.13 Oxidative Cleavage / Elaboration Common reducing agents include dimethyl sulfide (DMS) and Zn/H2O. Practice with SkillBuilder 8.8 – Predict the Products Copyright ©2021 John Wiley & Sons, Inc. 85 8.13 Oxidative Cleavage / Practice Predict a bicyclic reactant used to form the product below Copyright ©2021 John Wiley & Sons, Inc. 86 8.13 Oxidative Cleavage / Practice Answer Predict a bicyclic reactant used to form the product below Copyright ©2021 John Wiley & Sons, Inc. 87 8.14 Predicting Products of Addition Rxns 1. Analyze the reagents used to determine what groups will be added across the C=C double bond 2. Determine the regioselectivity (Markovnikov or anti-Markovnikov) 3. Determine the stereospecificity (syn or anti addition) The more familiar you are with the mechanisms and the Chapter 8 reagents, the easier predicting products will be Practice with SkillBuilder 8.9 – Predict the Products Copyright ©2021 John Wiley & Sons, Inc. 88 8.15 One-Step Syntheses / Planning To plan a synthesis, assess the reactants and products to see what changes need to be made Addition Reaction (Chapter 8) Substitution Reaction (Review SkillBuilder 7.8) Elimination Reaction (Review SkillBuilder 7.9) Copyright ©2021 John Wiley & Sons, Inc. 89 8.15 One-Step Syntheses / Practice To plan a synthesis, assess the reactants and products to see what changes need to be made Give reagents and conditions for the following: addition reaction add H and OH Markovnikov regiochem. Copyright ©2021 John Wiley & Sons, Inc. 90 8.15 One-Step Syntheses / Practice Answer To plan a synthesis, assess the reactants and products to see what changes need to be made Give reagents and conditions for the following: Practice with additional examples in SkillBuilder 8.10 – Propose a Synthesis Copyright ©2021 John Wiley & Sons, Inc. 91 8.15 Changing Position of a Halogen or OH / Two Reactions Changing the position of a halogen The following transformation cannot be done with a single reaction: It can be accomplished in a two-reaction sequence: Copyright ©2021 John Wiley & Sons, Inc. 92 8.15 Changing Position of a Halogen or OH / Carefully Choose the Base Changing the position of a halogen To do the elimination reaction, the base needs to be carefully chosen: This is the alkene we need, so we use a non-bulky base Copyright ©2021 John Wiley & Sons, Inc. 93 8.15 Changing Position of a Halogen or OH / Choose Reagents Changing the position of a halogen Next, we need to decide the reagents needed to add H and Br: Markovnikov addition of H and Br The overall elimination-addition sequence is as follows: Copyright ©2021 John Wiley & Sons, Inc. 94 8.15 Changing Position of a Halogen or OH / More Complex Example Consider the following transformation: This is not a simple substitution, addition or elimination, so two processes must be combined Copyright ©2021 John Wiley & Sons, Inc. 95 8.15 Changing Position of a Halogen or OH / Hoffmann Product The elimination must be done to give the Hofmann alkene, via an E2 elimination The alcohol must be changed to a good leaving group so we can use a bulky base to afford the Hofmann product: Copyright ©2021 John Wiley & Sons, Inc. 96 8.15 Changing Position of a Halogen or OH / Summary The addition reaction must give anti-Markovnikov addition of H and OH The overall elimination-addition sequence is as follows: Practice with SkillBuilder 8.11 – Changing the Position of a Group Copyright ©2021 John Wiley & Sons, Inc. 97 8.15 Changing the Position of a π Bond / Addition and Elimination Changing the position of a π bond: Again, two processes must be combined Anti-Markovnikov addition Elimination to give of H and Br the Hofmann product Copyright ©2021 John Wiley & Sons, Inc. 98 8.15 Changing the Position of a π Bond / Summary Changing the position of a π bond Now recall the reagents needed for each reaction: Anti-Markovnikov Elimination to give the addition of H and Br Hofmann product HBr, ROOR (anti- t-BuOK (bulky base) Markovnikov) Practice with SkillBuilder 8.12 – Changing position of π Bond Copyright ©2021 John Wiley & Sons, Inc. 99 Ch. 8 Review of Alkene Reactions Ten reactions of alkenes covered in this chapter: 1. Hydrohalogenation (Markovnikov) 2. Hydrohalogenation (anti-Markovnikov) 3. Acid-catalyzed hydration and oxymercuration-demercuration 4. Hydroboration-oxidation 5. Hydrogenation 6. Bromination 7. Halohydrin formation 8. Anti dihydroxylation 9. Syn dihydroxylation 10. Ozonolysis Copyright ©2021 John Wiley & Sons, Inc. 100 Ch. 8 Review of Alkene Reactions (cont. 1) Copyright ©2021 John Wiley & Sons, Inc. 101 Ch. 8 Review of Alkene Reactions (cont. 2) Copyright ©2021 John Wiley & Sons, Inc. 102 Mechanism 8.1 & 8.2 Review – Add Arrows Copyright ©2021 John Wiley & Sons, Inc. 103 Mechanism 8.3 Review – Add Arrows Copyright ©2021 John Wiley & Sons, Inc. 104 Mechanisms 8.4 & 8.5 Review – Add Arrows Copyright ©2021 John Wiley & Sons, Inc. 105 Mechanism 8.6 Review – Add Arrows Copyright ©2021 John Wiley & Sons, Inc. 106