Ethers and Epoxides

Question 1

what reaction converts ROH into ethers

Answer 1

Williamson ether synthesis

Question 2

what are the two types of williamson ether synthesis

Answer 2

intermolecular, and intramolecular

Question 3

what reagents are needed for Williamson ether synthesis

Answer 3

strong base, and an electrophile

Question 4

what are examples of strong bases used for Williamson ether synthesis

Answer 4

LDA, BuLi

Question 5

what is the product of intermolecular Williamson ether synthesis

Answer 5

ether

Question 6

what is the product of intramolecular Williamson ether synthesis

Answer 6

cyclic ether

Question 7

what is the mechanism for williamson ether synthesis

Answer 7

Sn2

Question 8

characteristics of intermolecular Williamson ether synthesis

Answer 8

between molecules, slow

Question 9

characteristics of intramolecular Williamson ether synthesis

Answer 9

within a molecule, fast

Question 10

why are ethers great solvents

Answer 10

they react with very few reagents

Question 11

characteristics of ethers

Answer 11

• stable in basic conditions
• resistant to nucleophilic attack

Question 12

what is the mechanism for acidic cleavage of ethers

Answer 12

1. proton transfer
2. Sn2

Question 13

what dictates the reactivity of hydrogen halides toward the cleavage of ethers

Answer 13

their general acidity and nucleophilicity
HI > HBr&raquo_space; HCl

Question 14

what kinds of ethers undergo acid cleavage via Sn1 and what do they form

Answer 14

tertiary, allylic, and benzylic ethers (study what these are); form stable carbocation intermediates

Question 15

what is the reagent for acidic cleavage of ethers

Answer 15

binary acid

Question 16

what is the product of acidic cleavage of ethers

Answer 16

alcohol

Question 17

what is the mechanism of acid cleavage via Sn1 to form stable carbocation intermediates

Answer 17

1. proton transfer (forms oxonium)
2. leaving group leaves (forms benzylic or vinylic carbocation)

Question 18

what is the relative acidity between hydroxyl protons and terminal alkynes

Answer 18

hydroxyl protons > terminal alkynes

Question 19

protecting groups characteristics

Answer 19

• easily added to the sensitive functional group
• resistant to the reagents used to transform the unprotected functional group or groups
• easily removed to regenerate the original functional group

Question 20

what are the steps of the protection of -OH groups

Answer 20

1. protect
2. react
3. deprotect

Question 21

what reagent is used to protect -OH

Answer 21

TMSCl or ROTMS

Question 22

what is the reactant for protection of -OH

Answer 22

1,2-difunctionalized group with a functional group that should react instead of the alcohol group

Question 23

what are the good protecting groups

Answer 23

TMSCl (trimethylsilyl chloride), and ROTMS (a silyl ether)

Question 24

what reagent can be used to deprotect

Answer 24

Bu_4N^+F^-

Question 25

what is an epoxide

Answer 25

cyclic ether

Question 26

what is the most acidic proton site on an epoxide

Answer 26

the alcohol

Question 27

is alkoxide a good nucleophile or electrophile

Answer 27

nucleophile

Question 28

which Sn2 attack is faster: intramolecular or intermolecular?

Answer 28

intramolecular

Question 29

what are the steps of intramolecular Williamson synthesis of epoxides

Answer 29

1. proton transfer 2. cyclization via Sn2

Question 30

what is the purpose of Williamson synthesis of epoxides

Answer 30

turning an alkane alcohol into an epoxide

Question 31

what is the purpose of synthesis of epoxide with peroxycarboxylic acids

Answer 31

create an epoxide from an alkene

Question 32

what reagent is required to synthesize an epoxide from an alkenee

Answer 32

mCPBA with an aprotic solvent (usually CH2Cl2)

Question 33

what are the two precursors to an epoxide

Answer 33

1. halohydrin 2. epoxidation of alkene

Question 34

how does stereochem affect epoxidation of an alkene

Answer 34

cis alkene --> cis epoxide, trans alkene --> trans epoxide

Question 35

what reagents do you need for the two steps of a ring-opening reaction of epoxides

Answer 35

1. alkaline 2. protic

Question 36

what is the precursor to a 1,2-difunctionalized compound

Answer 36

epoxide

Question 37

what is the mechanism for the alkaline nucleophilic ring-opening of epoxides

Answer 37

Sn2, then proton transfer

Question 38

what do you do if there is an alkoxide with an sp3 C

Answer 38

take a traditional proton transfer

Question 39

what intermediate forms when the ring-opening step occurs in alkaline conditions

Answer 39

alkoxide

Question 40

which carbon does the nucleophile attack in an acid-catalyzed ring-opening

Answer 40

more substituted carbon

Question 41

what are commonly used H-Nu for synthesizing 1,2-difunctionalized alcohols

Answer 41

H3O+, ROH; H3O+; HX

Question 42

why is stereochemistry variable in ring opening of epoxides

Answer 42

- nucleophile backside-attacks the carbon atom (opposite side from LG) - attached methyl group is repelled away by nucleophile