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Organic Chemistry Reviews Chapter 11

This chapter explores the fundamental differences and properties of alcohols and ethers. Alcohols, characterized by the -OH group, exhibit strong hydrogen bonding, influencing their boiling points and reactivity. In contrast, ethers, with an oxygen atom between two hydrocarbon chains, are less polar and inert. The synthesis of alcohols via hydration, oxymercuration/demercuration, and hydroboration-oxidation is detailed, alongside benefits and drawbacks of each method. The conversion of alcohols to alkyl halides is addressed, highlighting mechanisms and regio-chemistry implications.

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Organic Chemistry Reviews Chapter 11

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  1. Organic Chemistry ReviewsChapter 11 Cindy Boulton February 8, 2009

  2. Alcohol vs Ethers • Alcohol • CH3OH • IUPAC: methanol • Radiofuntional name: methyl alchol • Ether • CH3OCH3 • IUPAC: methoxymethane • Radiofunctional name: dimethyl ether

  3. Alcohol Chemistry and Properties • Determined by –OH group • -OH is a polar covalent bond • Cable of hydrogen bond • Raises boiling point • Strong dipole • Hydrogen has a pKa = 17 • Readily removed by a strong base • Dissolves polar and ionic compounds

  4. Ether Chemistry and Properties • Oxygen has a partial negative charge • Two Carbons attached have a partial positive charge • Charges partially cancelled each other out • Not as polar or reactive • Used as a solvent • Inert: not as reactive

  5. Synthesis of Alcohols • Hydration of alkenes • By aqueous Sulfuric Acid (H+) • Regiochemistry: Markovinkov, incoming hydrogen goes to carbon with more hydrogen’s and forms a stable carbon cation • Stereochemistry: Racemic, an equal amount of new stereocenters (R and S) are formed • Pros: • Sulfuric Acid is cheap • Eliminate multiple steps (easy) • Cons: • Primary R-OH is difficult to make • Skeletal rearrangement is possible, carbocation will rearrange to a higher order

  6. Synthesis of Alcohols • Oxymercuration/Demercuration • Alkene reacts with 1) Hg(OAc)2 2) NaBH4, OH- • Hg has multiple bonds and partial bonds with carbocation • Blocks alkanide migration/skeletal rearrangement • Regiochemistry: Markovinkov • Stereochemistry: Racemic • Pros: • Skeletal rearrangement is blocked • Cons: • Hg is toxic and expensive • 2 Steps and multiple clean up steps • Lower overall yield • Primary Alcohols not likely formed

  7. Synthesis of Alcohols • Hydroboration-oxidation • Alkene reacts with 1) BH3 2) H2O2, OH- • Tranistion State: Boron and Hydrogen bonds to both Carbons, forms a trialkylborane • Regiochemistry: Antimarkovinkov-incoming Hydrogen goes to Carbon with less Hydrogen, Sterics • Stereochemistry: Racemic, Syn addition • Pros: • Can make Primary Alcohol • No Skeletal rearrangement • Cons: • 2 Steps • Costly • Needs clean up

  8. Sulfonates • Good leaving group for SN1, SN2, E1, and E2 reactions • Stable ions and unreactive • Resonance Structure • Strong inductive effect • Alcohol is a bad leaving group but is changed to a have a sulfonate • Triflate (Tf): best • Tosylate (Tf) • Mesylate : worst

  9. Conversion of Alcohols to Alkyl Halides • Alcohol is a poor leaving group, but a halide is a good leaving group for another reaction • Conversion by HX (X = Cl, Br, I), PBr3, and SOCl2 • 1o Alcohol Mechanism • “SN2”- retains stereochemistry, no carbocation intermediate • 3o Alcohol Mechanism • “SN1”- sterics from the –R groups block SN2 reaction • A stable carbocation intermediate is fromed • Product is a racemic mixture with Optical Rotation = 0o • 2o Alcohol Mechanism • Either “SN1” or “SN2” depending on the –R groups • Identified by optical rotation

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