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Chem 30B > Ethers and Epoxides > Flashcards

Ethers and Epoxides Flashcards

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1
Q

what reaction converts ROH into ethers

A

Williamson ether synthesis

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2
Q

what are the two types of williamson ether synthesis

A

intermolecular, and intramolecular

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3
Q

what reagents are needed for Williamson ether synthesis

A

strong base, and an electrophile

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4
Q

what are examples of strong bases used for Williamson ether synthesis

A

LDA, BuLi

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5
Q

what is the product of intermolecular Williamson ether synthesis

A

ether

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6
Q

what is the product of intramolecular Williamson ether synthesis

A

cyclic ether

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7
Q

what is the mechanism for williamson ether synthesis

A

Sn2

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8
Q

characteristics of intermolecular Williamson ether synthesis

A

between molecules, slow

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9
Q

characteristics of intramolecular Williamson ether synthesis

A

within a molecule, fast

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10
Q

why are ethers great solvents

A

they react with very few reagents

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11
Q

characteristics of ethers

A
  • stable in basic conditions
  • resistant to nucleophilic attack
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12
Q

what is the mechanism for acidic cleavage of ethers

A
  1. proton transfer
  2. Sn2
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13
Q

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

A

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

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14
Q

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

A

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

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15
Q

what is the reagent for acidic cleavage of ethers

A

binary acid

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16
Q

what is the product of acidic cleavage of ethers

A

alcohol

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17
Q

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

A
  1. proton transfer (forms oxonium)
  2. leaving group leaves (forms benzylic or vinylic carbocation)
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18
Q

what is the relative acidity between hydroxyl protons and terminal alkynes

A

hydroxyl protons > terminal alkynes

19
Q

protecting groups characteristics

A
  • 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
20
Q

what are the steps of the protection of -OH groups

A
  1. protect
  2. react
  3. deprotect
21
Q

what reagent is used to protect -OH

A

TMSCl or ROTMS

22
Q

what is the reactant for protection of -OH

A

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

23
Q

what are the good protecting groups

A

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

24
Q

what reagent can be used to deprotect

A

Bu_4N^+F^-

25
Q

what is an epoxide

A

cyclic ether

26
Q

what is the most acidic proton site on an epoxide

A

the alcohol

27
Q

is alkoxide a good nucleophile or electrophile

A

nucleophile

28
Q

which Sn2 attack is faster: intramolecular or intermolecular?

A

intramolecular

29
Q

what are the steps of intramolecular Williamson synthesis of epoxides

A
  1. proton transfer
  2. cyclization via Sn2
30
Q

what is the purpose of Williamson synthesis of epoxides

A

turning an alkane alcohol into an epoxide

31
Q

what is the purpose of synthesis of epoxide with peroxycarboxylic acids

A

create an epoxide from an alkene

32
Q

what reagent is required to synthesize an epoxide from an alkenee

A

mCPBA with an aprotic solvent (usually CH2Cl2)

33
Q

what are the two precursors to an epoxide

A
  1. halohydrin
  2. epoxidation of alkene
34
Q

how does stereochem affect epoxidation of an alkene

A

cis alkene –> cis epoxide, trans alkene –> trans epoxide

35
Q

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

A
  1. alkaline
  2. protic
36
Q

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

A

epoxide

37
Q

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

A

Sn2, then proton transfer

38
Q

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

A

take a traditional proton transfer

39
Q

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

A

alkoxide

40
Q

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

A

more substituted carbon

41
Q

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

A

H3O+, ROH; H3O+; HX

42
Q

why is stereochemistry variable in ring opening of epoxides

A
  • nucleophile backside-attacks the carbon atom (opposite side from LG)
  • attached methyl group is repelled away by nucleophile
43
Q
A

Chem 30B (5 decks)

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