Organic Chemistry ReviewsChapter 11
Cindy Boulton
February 8, 2009
Alcohol vs Ethers Alcohol
CH3OH IUPAC: methanol Radiofuntional name: methyl alchol
Ether CH3OCH3
IUPAC: methoxymethane Radiofunctional name: dimethyl ether
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
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
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
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
Synthesis of Alcohols Hydroboration-oxidation
Alkene reacts with 1) BH3 2) H2O2, OH-
Tranistion State: Boron and Hydrogen bonds to both Carbons, forms a trialkyl borane
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
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
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
Synthesis of Ethers Dehydration of alcohol
An alcohol reacts with H+ to protonate the –OH Second alcohol acts as a nucleophile and H2O acts
as a good leaving group Oxygen is protonated and removed by water of
something else forming symmetric or asymmetric ethers.
Reacts at an optimal temperature for the alcohol At different temperature can form an alkene
Synthesis of Ethers Williamson Synthesis
Alcohol reacts with a sulfonate and base to form a good leaving group The smaller of the two alcohols If the larger alcohol had been used, sterics would have
prevented the small nucleophile from attacking and an alkene would have been formed in an E2 reaction
A second alcohol reacts with a strong base to remove the proton on the hydroxyl forming an alkoxide, a good nucleophile The larger of the two alcohols
Control synthesis forming the ether using an SN2 reaction
Reaction of Ethers Cleaved by strong acids at high temperature
The ether becomes protonated by the acid forming an oxonium (O+)
The acid acts as a nucleophile attacking one of the Carbon groups
An acid and alcohol is formed A second acid reacts with the alcohol, protonating
the hydroxyl group The acid acts as a nucleophile reacting with the
carbon group Overall products: 2 alkyl halides and H2O
Epoxides Oxiranes or cyclooxapropanes Cyclic ether
2 Carbons and 1 Oxygen in a ring shape Strained and reactive
Synthesis of Epoxides Alkene reacts with a peroxy acid Oxygen connected to the –H reacts with the
alkene Forms enantiomers and racemic mixture
Epoxides Base Catalyzed Ring Opening
Hydroxyl attacks the carbon that is less crowded due to sterics
Oxygen remains bound to more crowded Carbon and is protonated
Forms a trans-alcohol due to anti addition Acid Catalyzed Ring Opening
Oxygen is protonated forming an oxonium Incoming H2O molecule attacks more substituted carbon
which forms a more stable carbocation due to electronics H2O molecule is deprotonated by a water molecule Forms a trans-alcohol due to anti addition
Give enantiomers of same original molecule Different from Syn Hydroxylation
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