Ch 18: Ethers and Epoxides

Question 1

What are the two methods for naming ethers?

Answer 1

Common naming and IUPAC nomenclature

Common naming involves naming each alkyl or aryl group, while IUPAC naming treats the longer carbon chain as the parent structure.

Question 2

In common naming of ethers, how are the alkyl or aryl groups arranged?

Answer 2

Alphabetically

The name ends with ‘ether’.

Question 3

What is the IUPAC name for CH3OCH2CH3?

Answer 3

Methoxyethane

The longer carbon chain is treated as the parent structure.

Question 4

What characterizes epoxides?

Answer 4

Cyclic ethers containing a three-membered ring

They are also known as oxiranes.

Question 5

How is an epoxide named when considered as a substituted oxirane?

Answer 5

Numbering starts at the oxygen

Substituents are numbered based on priority rules.

Question 6

What is the parent name used in epoxide naming when derived from an alkene?

Answer 6

The corresponding alkene

The oxygen bridge is indicated by the ‘epoxy’ prefix.

Question 7

What is the mechanism of Williamson Ether Synthesis?

Answer 7

SN2 reaction between an alkoxide ion and a primary alkyl halide

The alkoxide acts as a nucleophile.

Question 8

What is a limitation of Williamson Ether Synthesis?

Answer 8

Works best with primary alkyl halides

Secondary and tertiary halides may lead to elimination.

Question 9

What is the first step in the alkoxymercuration-demercuration mechanism?

Answer 9

Formation of a mercurium ion intermediate

This occurs after reacting alkenes with mercuric acetate and an alcohol.

Question 10

What products result from the acidic cleavage of ethers?

Answer 10

Alkyl halides and alcohols

Two alkyl halides if excess acid is used.

Question 11

What type of carbon does a strong nucleophile attack during the nucleophilic ring opening of epoxides under basic conditions?

Answer 11

The less substituted carbon

This follows an SN2-like mechanism.

Question 12

In acid-catalyzed ring opening of epoxides, which carbon does the nucleophile attack?

Answer 12

The more substituted carbon

This is due to a carbocation-like transition state.

Question 13

What is the conclusion regarding the naming of ethers and epoxides?

Answer 13

Ethers are named using alkoxy substituents and epoxides as oxiranes or epoxy alkanes

This summarizes their nomenclature and structural characteristics.

Question 14

What are the two efficient methods for preparing ethers?

Answer 14

Williamson ether synthesis and alkoxymercuration-demercuration

These methods leverage different mechanisms for ether formation.

Question 15

True or False: Ethers react with strong acids to produce only alcohols.

Answer 15

False

Ethers can produce alkyl halides as well.

Question 16

Fill in the blank: The mechanism of acidic cleavage of ethers involves _______ the ether oxygen.

Answer 16

Protonating

This makes the ether more electrophilic.

Question 17

What is the IUPAC name for CH₃OCH₂CH₃?

Answer 17

Methoxyethane (ethyl methyl ether)

Methoxyethane is commonly known as ethyl methyl ether.

Question 18

How are symmetrical ethers named in IUPAC nomenclature?

Answer 18

Use the alkane name with ‘ether’ (e.g., diethyl ether)

This naming convention indicates the two identical alkyl groups attached to the ether.

Question 19

What is an epoxide?

Answer 19

A three-membered cyclic ether with an oxygen atom

Epoxides are highly reactive due to the strain in their three-membered ring.

Question 20

What is the common name for ethylene oxide?

Answer 20

Oxirane

Oxirane is used in various chemical syntheses and is a key intermediate in organic chemistry.

Question 21

What is the structure of tetrahydrofuran (THF)?

Answer 21

A five-membered cyclic ether

THF is commonly used as a solvent in organic reactions.

Question 22

What reaction is commonly used to synthesize ethers?

Answer 22

Williamson Ether Synthesis (SN2 reaction)

This method involves the reaction of an alkoxide ion with a primary alkyl halide.

Question 23

What type of alkyl halides are best for the Williamson ether synthesis?

Answer 23

Primary alkyl halides (to avoid elimination)

Secondary and tertiary halides are less favorable due to competing elimination reactions.

Question 24

What is the product of CH₃O⁻ + CH₃CH₂Br in Williamson ether synthesis?

Answer 24

Methoxyethane (ethyl methyl ether)

This reaction exemplifies the formation of an ether from an alkoxide and an alkyl halide.

Question 25

What reagent is required to convert an alcohol into an ether via acid-catalyzed dehydration?

Answer 25

H₂SO₄ or H₃PO₄ (Strong acid) ## Footnote These acids facilitate the elimination of water from alcohols, forming ethers.

Question 26

What is the major product of the reaction between an alcohol and a strong acid at high temperatures?

Answer 26

An alkene (elimination reaction occurs) ## Footnote This process typically involves dehydration of the alcohol.

Question 27

Why are ethers relatively unreactive?

Answer 27

They lack acidic protons and strong leaving groups ## Footnote This stability makes ethers less reactive than other functional groups.

Question 28

What reagents can cleave ethers?

Answer 28

Strong acids (HI, HBr) via SN1 or SN2 mechanisms ## Footnote The cleavage results in the formation of alcohols and alkyl halides.

Question 29

What is the major product when diethyl ether reacts with excess HI?

Answer 29

Ethanol and iodoethane ## Footnote This reaction demonstrates the cleavage of the ether bond.

Question 30

How does epoxide ring-opening differ under acidic and basic conditions?

Answer 30

Acidic: Attack at the more substituted carbon; Basic: Attack at the less substituted carbon ## Footnote This difference is crucial for regioselectivity in reactions involving epoxides.

Question 31

What is the product of epoxide hydrolysis under acidic conditions?

Answer 31

A trans-1,2-diol ## Footnote This reaction involves the addition of water across the epoxide ring.

Question 32

What is the product when an epoxide reacts with CH₃MgBr?

Answer 32

A primary alcohol after acidic workup ## Footnote This reaction illustrates the nucleophilic attack of a Grignard reagent on an epoxide.

Question 33

How does NaOH affect epoxides?

Answer 33

It causes nucleophilic attack at the less substituted carbon ## Footnote This process is characteristic of basic conditions and leads to regioselective opening of the epoxide.

Question 34

What is the stereochemical outcome of epoxide opening?

Answer 34

Anti-addition (trans product) ## Footnote This stereoselectivity is a result of the mechanism of epoxide ring-opening.

Question 35

What reagent can selectively convert an alkene to an epoxide?

Answer 35

mCPBA (meta-chloroperoxybenzoic acid) ## Footnote This reagent is commonly used in organic synthesis for epoxidation reactions.

Question 36

What is the difference in regioselectivity between epoxide opening under acidic vs. basic conditions?

Answer 36

Acidic: More substituted attack; Basic: Less substituted attack ## Footnote Understanding this difference is vital for predicting product formation in synthetic pathways.