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UH CHEM 3332 - Substitution vs. Elimination

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CHEM 3332 1st Edition Lecture 3Outline of Last Lecture Alkene Oxidations: (addition of oxygen)A. Epoxidation with peroxyacidsAcid – catalyzed ring opening of epoxideB. HydroxylationC. Oxidative CleavageAddition Mechanisms Continued: Additions of Alkynes A. Additions of H – X: similar to address to alkenes – intermediate is more stable C+ (Mark’s Rule)B. Addition of X2: 3-membered ring intermediate probably too strained; forms more stable C+ addition of first eq. X2 gives cis and trans productsC. Addition of H2: 3 choices 1. Gives alkane with H2 and active catalyst (Pt,Pd,Ni)2. Gives cis-alkene with H2 and Pd/Baso4/quinoline (Lindlar’s catalyst)3. Gives trans-alkene with Na or Li in liquid ammoniaD. Addition of H-OH: Does not give alcohols!1. Mark addition2. Non-Mark additionOxidation of alkynes:1. Mild2. StrongII/III. Elimination/Substitution Reactions:For Pathway A, E+ is δ+ Carbon = substitutionFor Pathway B, E+ is δ+ Hydrogen = emilinationSN1/E1: reactivity: 3 > 2 >1 >>> CH3 Step 1:Step 2:SN2:E2:Pathway that has the fastest rxn rate (lowest Ea/lowest E TS) forms major product – anticoplanarOutline of Current Lecture Substitution vs. Elimination (Wade summaries: sections 6-16 and 6-22)Exception: 1 halide with a strong, unhindered base – SN2 gives major productExamples: 1.2.3.4.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.5.Synthesis of AlcoholsI. From Alkyl HalidesII. From Alkenes: Ch. 8A. Hydration (H3O+) = Mark/Inversion/RetentionB. Oxymercuration/ Demercuration: 1. Hg(OAC)2/H2O 2. NaBH4 = Mark /Anti additionC. Hydroboration: 1. BH3THF 2. H2O2/OH- = Non-Mark/Syn additionD. Epoxidation followed by an acidic hydrolysis: 1. MCPBA 2. H3O+ or CH3CO3H/H3O+ = Trans vicinal diolE. Hydroxylation: OsO4/H2O2 or cold, basic KMnO4 = Syn vicinal diolIII.From Acetylide Anion and Carbonyl Compound: Ch.9IV. Organometallic Reagents + Carbonyl Compounds → R-OH: Ch.10A. Preparation of Reagents1.2.B. Mechanism of Grignard Reaction (mechanism of organolithium reaction is similar)1. With aldehydes and ketones:2. With esters or acid halidesV. Reduction of CarbonylsA. Hydride ReductionsReducing AgentsNaBH4: the milder choice: usually chosen for aldehydes and keytones- May use H2O or alcohol as solvents- Very slow reduction or esters; will not reduce acid chlorides or carboxylic acidsLiAlH4: more reactive than NaBH4- Reduced aldehydes, ketones, esters, acid halides and carboxylic acids- CAUTION: reacts violently with H2O and alcohols! Must use esters as solvents1. Reduction of aldehydes and keytones:2. Reduction of esters, acid halides and carboxylic acidsB. Catalytic Hydrogenation of Aldehydes and Ketones:- Catalytic reduction of carbonyl is slower than reduction of carbon-carbon double bond- Raney Ni is best catalystCurrent LectureSubstitution vs. Elimination (Wade summaries: sections 6-16 and 6-22)Exception: 1 halide with a strong, unhindered base – SN2 gives major productExamples: 1.2.3.4.5.Synthesis of AlcoholsHEAT R – X + -OH → R – O – H OR R – X + H – OH → R – O – HI. From Alkyl HalidesII. From Alkenes: Ch. 8A. Hydration (H3O+) = Mark/Inversion/RetentionB. Oxymercuration/ Demercuration: 1. Hg(OAC)2/H2O 2. NaBH4 = Mark /Anti additionC. Hydroboration: 1. BH3THF 2. H2O2/OH- = Non-Mark/Syn additionD. Epoxidation followed by an acidic hydrolysis: 1. MCPBA 2. H3O+ or CH3CO3H/H3O+ = Trans vicinal diolE. Hydroxylation: OsO4/H2O2 or cold, basic KMnO4 = Syn vicinal diolIII.From Acetylide Anion and Carbonyl Compound: Ch.9IV. Organometallic Reagents + Carbonyl Compounds (aldehyde/keytone/esters) → R-OH: Ch.10A. Preparation of ReagentsB. Mechanism of Grignard Reaction (mechanism of organolithium reaction is similar)1. With aldehydes and ketones:2. With esters or acid halidesV. Reduction of CarbonylsA. Hydride ReductionsReducing AgentsNaBH4: the milder choice: usually chosen for aldehydes and keytones- May use H2O or alcohol as solvents- Very slow reduction or esters; will not reduce acid chlorides or carboxylic acidsLiAlH4: more reactive than NaBH4- Reduced aldehydes, ketones, esters, acid halides and carboxylic acids- CAUTION: reacts violently with H2O and alcohols! Must use esters as solvents1. Reduction of aldehydes and keytones:2. Reduction of esters, acid halides and carboxylic acidsB. Catalytic Hydrogenation of Aldehydes and Ketones:- Catalytic reduction of carbonyl is slower than reduction of carbon-carbon double bond- Raney Ni is best


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