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Ochem 2 > Quiz 2 > Flashcards

Quiz 2 Flashcards

1
Q

Acidic Cleavage w/ ether

A
  • using HBr + heat to split an ether into two alkyl halides
  • xs HBr needed for two sets of proton transfer and Sn2 mechanism
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2
Q

What happens when a phenyl ether undergoes acidic cleavage

A

it becomes a phenyl alcohol + akyl halide, not two alkyl halides bc of sp2 hybridization on the ring

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3
Q

Epoxides

A

cyclic ethers w/ two carbons that have severe ring and torsional strain

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4
Q

What are the two ways you can prepare epoxides?

A
  1. MCPBA + Peroxy acid on a double bond
  2. NaOH on the products of a halohydrin addition reaction
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5
Q

Explain the mechanism of a Halohydrin epoxide preparation

A

NaOH deprotonates the OH which leads to an intramolecular Sn2 reaction to produce the epoxide

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6
Q

True or false?

Stereochem is preseved in the halohydrin preparation of epoxides but not the MCPBA+ peroxy acid work up

A

False, stereochem is preserved in both

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7
Q

What are the two ring opening reactions of epoxides?

A
  1. reaction with a good nuc
  2. Acid catalyzed ring opening
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8
Q

Acid catalyzed ring opening

A

makes the O in the epoxide into a better LG using an acid

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9
Q

What are the mechanistic steps to acid catalyzed ring opening?

A
  1. proton transfer
  2. nucleophilic attack
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10
Q

True or False?

The nucleophilic attack in the second step of acid catalyzed ring opening resembles only a SN2 reaction

A

False, it has SN2 and SN1 properties

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11
Q

What are the regiochemical rules for nucleophilic ring opening?

A

attack at the less substitued side

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12
Q

What are the regiochemical rules for acid catalyzed ring opening?

A

if the epoxide has a tertiary side that side will be attacked but if there is no tertiary side the less substitued side will be attacked

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13
Q

True or False?

You can get the same products from acid catalyzed ring opening that you do from nucleophilic ring opening

A

False, they have diff regiochemical rules which can give you diff products

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14
Q

Thiols

A

similar to alchols but with S (-SH), extremely nucleophilic

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15
Q

How do you prepare a thiol?

A

reacting a NaSH with an alkyl halide

alkyl halide can even be secondary bc SH is very nucleophilic

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16
Q

Mechanism for oxidizing thiols to disulfides

A
  1. Thiol +NaOH to deprotonate thiol
  2. Thiolate + Br2 to attack Br
  3. Nuc attack by another thiolate to kick off Br and form disulfide
17
Q

What are the reagents for reducing a disulfide to a thiol?

A

HCl and Zn

18
Q

Sulfide

A

similar to ethers but with S, more reactive than ethers

19
Q

How can you prepare a sulfide?

A

the sulfur equivalent of the williamson ether synthesis

still best if alkyl halide is primary

20
Q

What kind of reactions can sulfides undergo?

A

1.can act as a nucleophile and attack
2.can be attacked by a stronger nucleophile and act as a LG

21
Q

Diene

A

compound with two C=C bonds

22
Q

What are the three classes of dienes

A
  1. Isolated
  2. conjugated
  3. Cummulated
23
Q

Conjugated Diene

A

bonds are separated by one C/ one sigma bond

24
Q

How can you prepare a conjugated diene?

A

Double elimination with dihalide and a strong bulky base to prevent SN2

25
Q

What is more stable an isolated pi bond or conjugated pi bonds

A

conjugated is more stable than isolated but not more stable than single bonds

26
Q

When will you not see a mix of s-cis and s-trans products for a diene?

A

when the diene is ‘locked’ like in a ring conformation

27
Q

What is the mechanism for addition of HX with a diene

A
  1. proton transfer to create a resonance stabilized carbocation
  2. nuc attack to create two different products

proton is never added to 2 or 3 position in pt step

28
Q

Thermodynamic product

A

the product favored at high temperatures, the one with the most stable alkene product

29
Q

Kinetic Product

A

the product favored at low temperatures, has the most stable C+ intermediate

30
Q

What kind of pericylic reaction is Diels Alder

A

Cyclo addition

31
Q

True or False?

Diels Alder has one intermediate that is cylic

A

False, all pericylic reactions are concerted and Diels Alder is one so it has no intermediates

32
Q

Diels Alder is a — — cyclo addition reaction that is — dependent

A

4+2, Temperature

33
Q

What temperatures favor the reverse diels alder reaction?

A

above 200 degrees celcius

34
Q

Dienophile in Diels Alder reaction

A
  • electrophilic properties
  • performs best with ewg to lower the activation E
35
Q

Stereochem of Dienophile

A
  • stereochem is conserved
  • if the dienophile is E = anti product
  • if dienophile is Z = syn product
36
Q

Diene of Diels Alder

A
  • nucleophilic
  • diels alder can only happen if diene is cis but remember non locked dienes can have free rotation
37
Q

What is the endo preference?

A

substiuents of a bridged product would prefer to be facing down/ closer to the pi bond rather than out and away from the pi bond

Ochem 2 (7 decks)

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