1. Chapter 11 Alcohols and Ethers

2. Nomenclature Nomenclature of Alcohols (Sec. 4
Nomenclature Nomenclature of Alcohols (Sec. 4.3F) Nomenclature of Ethers
Chapter 11

3. Nomenclature Nomenclature of Ethers Common Names
The groups attached to the oxygen are listed in alphabetical order
IUPAC
Ethers are named as having an alkoxyl substituent on the main chain
Chapter 11

4. Ethers are described as symmetrical or unsymmetrical depending on whether the two groups bonded to oxygen are the same or different. Unsymmetrical ethers are also called mixed ethers. Diethyl ether is a symmetrical ether; ethyl methyl ether is an unsymmetrical ether. Cyclic ethers have their oxygen as part of a ring–they are heterocyclic compounds. Several have specific IUPAC
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5. Cyclic ethers can be named using the prefix oxa-
Three-membered ring ethers can be called oxiranes; Four-membered ring ethers can be called oxetanes
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6. Chapter 11

7. Physical Properties of Alcohols and Ethers
Ether boiling points are roughly comparable to hydrocarbons of the same molecular weight
Molecules of ethers cannot hydrogen bond to each other
Alcohols have considerably higher boiling points
Molecules of alcohols hydrogen bond to each other
Both alcohols and ethers can hydrogen bond to water and have similar solubilities in water
Diethyl ether and 1-butanol have solubilites of about 8 g per 100 mL in water
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8. Synthesis of Alcohols from Alkenes
Acid-Catalyzed Hydration of Alkenes
This is a reversible reaction with Markovnikov regioselectivity
HA = acid ex H2SO4 ( H+ HSO4-)
Oxymercuration-demercuration
This is a Markovnikov addition which occurs without rearrangement
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9. Organic Synthesis: Functional Group Transformations Using SN2 Reactions
Stereochemistry can be controlled in SN2 reactions
Chapter 6

10. Hydroboration-Oxidation
This addition reaction occurs with anti-Markovnikov regiochemistry and syn stereochemistry
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11. Chapter 11

12. Alcohols as Acids Alcohols have acidities similar to water
Sterically hindered alcohols such as tert-butyl alcohol are less acidic (have higher pKa values)
Why?
1. The conjugate base is not well solvated and so is not stable
2. the alkyl group is electron donated group, so the electrons density is increased on the -C-O-
Alcohols are stronger acids than terminal alkynes and primary or secondary amines
An alkoxide can be prepared by the reaction of an alcohol with sodium or potassium metal
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13. Chapter 11

14. Conversion of Alcohols into Alkyl Halides
Hydroxyl groups are poor leaving groups, and as such, are often converted to alkyl halides when a good leaving group is needed
Three general methods exist for conversion of alcohols to alkyl halides, depending on the classification of the alcohol and the halogen desired
Reaction can occur with phosphorus tribromide, thionyl chloride or hydrogen halides
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15. the Reaction of Alcohols + Hydrogen Halides
Alkyl Halides from
the Reaction of Alcohols + Hydrogen Halides
The order of reactivity is as follows
Hydrogen halide HI > HBr > HCl > HF
Type of alcohol 3o > 2o > 1o < methyl
Mechanism of the Reaction of Alcohols with HX
SN1 mechanism for 3o, 2o, allylic and benzylic alcohols
These reactions are prone to carbocation rearrangements
In step 1 the hydroxyl is converted to a good leaving group
In step 2 the leaving group departs as a water molecule, leaving behind a carbocation
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16. Primary and methyl alcohols undergo substitution by an SN2 mechanism
In step 3 the halide, a good nucleophile, reacts with the carbocation
Primary and methyl alcohols undergo substitution by an SN2 mechanism
Primary and secondary chlorides can only be made with the assistance of a Lewis acid such as zinc chloride
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17. Alkyl Halides from the Reaction of Alcohols with PBr3 and SOCl2
These reagents only react with 1o and 2o alcohols in SN2 reactions
In each case the reagent converts the hydroxyl to an excellent leaving group
No rearrangements are seen
Reaction of phosphorous tribromide to give alkyl bromides
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18. Synthesis of Ethers
Ethers (symetrical) by Intermolecular Dehydration of Alcohol
Primary alcohols can dehydrate to ethers
This reaction occurs at lower temperature than the competing dehydration to an alkene
This method generally does not work with secondary or tertiary alcohols because elimination competes strongly
The mechanism is an SN2 reaction
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19. Williamson Ether Synthesis
This is a good route for synthesis of unsymmetrical ethers
The alkyl halide (or alkyl sulfonate) should be primary to avoid E2 reaction
Substitution is favored over elimination at lower temperatures
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20. Reactions of Ethers
Acyclic ethers are generally unreactive, except for cleavage by very strong acids to form the corresponding alkyl halides
Dialkyl ethers undergo SN2 reaction to form 2 equivalents of the alkyl bromide
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21. Epoxides Epoxides are three-membered ring cyclic ethers
These groups are also called oxiranes
Epoxides are usually formed by reaction of alkenes with peroxy acids
This process is called epoxidation and involves syn addition of oxygen
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22. Reaction of Epoxides
Epoxides are considerably more reactive than regular ethers
The three-membered ring is highly strained and therefore very reactive
Acid-catalyzed opening of an epoxide occurs by initial protonation of the epoxide oxygen, making the epoxide even more reactive
Acid-catalyzed hydrolysis of an epoxide leads to a 1,2-diol
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23. In unsymmetrical epoxides, the nucleophile attacks primarily at the most substituted carbon of the epoxide
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24. Base-catalyzed reaction with strong nucleophiles (e. g
Base-catalyzed reaction with strong nucleophiles (e.g. an alkoxide or hydroxide) occurs by an SN2 mechanism
The nucleophile attacks at the least sterically hindered carbon of the epoxide
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25. Chapter 11