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Organic Chemistry > Ch. 9 - Week 2 (Quiz 2) > Flashcards

Ch. 9 - Week 2 (Quiz 2) Flashcards

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1
Q

Why do 1,2 shifts occur?

A

to make a more stable carbocation

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2
Q

What is a 1,2-methyl shift?

A

when a 2º carbon becomes a 3º carbon by movement of a methyl group from adjacent carbon to carbocation

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3
Q

When might a 1,2 shift occur from 2º to 2º or 3º to 3º?

A

if the carbocation will be resonance stabilized

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4
Q

What should you do if a carbocation can undergo both 1,2-hydride and 1,2-methyl shift?

A

do both and show all possible products

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5
Q

What are SM and products of halodehydration-alkyl halid synth?

A 
SM = alcohol
Prod = alkyl halide
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6
Q

What are reagents of halodehydration alkyl halide synthesis?

A

HX (X = Cl, Br, I)

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7
Q

If HCl is used for Sn2 and primary alcohol (chlorodehydration), what also must be used?

A

ZnCl2

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8
Q

What type of mechanism is halodehydration alkyl halid synthesis?

A

Sn1 for 2º, 3º and 1º allylic/benzylic

Sn2 for 1º alcohol

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9
Q

What are the two major steps of of halodehydration alkyl halide synthesis?

A

protonation of OH to make good leaving group, substitution of X

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10
Q

Can RAR occur for halodehydration alkyl halide synth?

A

Yes, for 2º, 3º and allylic/benzylic 1º

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11
Q

What is the solvent for halodehydration alkyl halide synthesis?

A

HX is considered to be solvent

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12
Q

What are SM and P of POCl3 mediated alcohol dehydration (alkene synthesis)?

A 
SM = alcohol
P = alkene
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13
Q

What are reagents of POCl3 mediated alcohol dehydration (alkene synthesis)?

A

POCl3 and pyridine

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14
Q

What type of mechanism is POCl3 mediated alcohol dehydration (alkene synthesis)?

A

always E2 no matter alcohol substitution

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15
Q

What are major steps of POCl3 mediated alcohol dehydration (alkene synthesis)?

A

alcohol binds to POCl3 which makes it lose a Cl

pyridine takes proton off to make good leaving group

pyridine take beta H via E2 to make alkene

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16
Q

Can RAR occur for POCl3 mediated alcohol dehydration (alkene synthesis)?

A

No, E2 so no carbocation

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17
Q

What is an important stereochemical consideration for POCl3 mediated alcohol dehydration (alkene synthesis)?

A

alpha C and beta H must be antiperiplanar!

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18
Q

What is solvent for POCl3 mediated alcohol dehydration (alkene synthesis)?

A

pyridine

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19
Q

What are SM and P of of chlorodehydration with SOCl2 (alkyl chloride synthesis)?

A 
SM = 1º or 2º alcohol
P = alkyl chloride
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20
Q

What are reagents for chlorodehydration with SOCl2 (alkyl chloride synthesis)?

A

SOCl2 (thionyl chloride)

pyridine or other 3º amine

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21
Q

What type of mechanism is chlorodehydration with SOCl2 (alkyl chloride synthesis)?

A

Sn2 only so NR for 3º

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22
Q

What are major steps of chlorodehydration with SOCl2 (alkyl chloride synthesis)?

A

alcohol reacts with POCl2

pyridine proton sponge takes proton off O

Cl- attacks alpha carbon in Sn2 rxn

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23
Q

Can RAR occur fpr chlorodehydration with SOCl2 (alkyl chloride synthesis)?

A

No, Sn2 so no carbocation

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24
Q

What stereochemical considerations are there for chlorodehydration with SOCl2 (alkyl chloride synthesis)

A

Sn2 so inversion at alpha carbon if being attacked

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25
What is solvent for chlorodehydration with SOCl2 (alkyl chloride synthesis)?
amine base (polar / aprotic)
26
What are SM and P of bromodehydration with PBr3 (alkyl bromide synthesis)?
``` SM = 1º or 2º alcohol only P = alkyl bromide ```
27
What are reagents of for bromodehydration with PBr3 (alkyl bromide synthesis)?
PBr3 and pyridine (or Br-)
28
What type of mechanism is bromodehydration with PBr3 (alkyl bromide synthesis)?
Sn2 only! so NR for 3º alcohols
29
What are major steps of bromodehydration with PBr3 (alkyl bromide synthesis)?
O grabs P which makes carbon electrophilic and converts OH to good LG Pyridine proton sponge removes H, now activated alcohol Sn2 only! to make alkyl bromide
30
Can RAR occur for bromodehydration with PBr3 (alkyl bromide synthesis)?
No, Sn2 so no carbocations form
31
What stereochemical considerations are there for bromodehydration with PBr3 (alkyl bromide synthesis)?
Sn2 rules so inversion at alpha carbon if st. center
32
What is solvent for bromodehydration with PBr3 (alkyl bromide synthesis)?
amine base
33
What is tosylate?
derivative of alcohol that is THE BEST LG!!
34
How are alcohols converted to tosylates?
Tosylation with TsCl
35
Why is tosylate a good LG?
because its conjugate acid is tosic acid which is strong (pKa = -7)
36
Why are alkyl tosylates called the "middle man"?
they are rarely the final product of synthesis, usually they are a synthetic intermediate
37
Is alpha carbon electrophilic when bonded to OH?
No, only when OH becomes good LG
38
What are SM and P for tosylation with TsCl?
``` SM = alcohol (any sub, Csp3 not required) P = alkyl tosylate ```
39
What are reagents of tosylation with TsCl?
TsCl and pyridine
40
What type of mechanism is tosylation with TsCl?
oxygen binds to Ts and kicks off Cl... not Sn2 (but can go under Sn2 after it becomes alkyl tosylate)
41
What are major steps of tosylation with TsCl?
oxygen of hydroxyl group graphs S of Ts and kicks off Cl pyridine proton sponge grabs proton which gives e- to oxygen to become alkyl tosylate
42
Can RAR occur or tosylation with TsCl?
No, not a chance for carbocations
43
What are the stereochemical considerations for tosylation with TsCl?
NO inversion at alpha carbon because reaction takes place at hydroxyl carbon inversion only occurs if alkyl tosylate undergoes Sn2 afterwards
44
What is solvent for tosylation with TsCl?
polar aprotic
45
Do epoxides have a good LG? Why are they reactive?
No good LG but they are highly strained with 2 polar bonds so they are pretty reactive (ring-opening is favored)
46
What are five nucs that can open an epoxide ring?
-OH, -OR, -CN, -SR, NH3
47
What is SM and P of nucleophilic epoxide opening?
``` SM = epoxide P = alcohol ```
48
What are reagents of nucleophilic epoxide opening?
strong anionic nucleophile and H2O
49
Why is nucleophilic epoxide opening considered to be a regioselective reaction?
nuc only attacks at less sterically hindered carbon
50
What type of mechanism is nucleophilic epoxide opening?
Sn2
51
What are major steps of nucleophilic epoxide opening?
strong anionic nuc attacks less sub'd carbon on epoxie via Sn2 (makes alkoxide) water protonates oxygen in water quenching to neutralize negative charge and create an alcohol
52
Can RAR occur for nucleophilic epoxide opening?
No, Sn2
53
What are stereochemical considerations for nucleophilic epoxide opening?
Sn2 so inversion at attacked carbon (but doesn't mean dashes and wedges just switch) if it is a symmetrical epoxide, it will still be Sn2 but both carbons are attacked equally so a racemic mixture will form
54
What is solvent for nucleophilic epoxide opening?
polar aprotic
55
What are SM and P of acid-catalyzed epoxide opening?
``` SM = epoxide P = alcohol ```
56
What are reagents of acid-catalyzed epoxide opening?
HX and Nu-H or strong acid (TsOH and H2So4) and neutral nuc
57
What is mechanism of acid-catalyzed epoxide opening?
Sn2-like
58
What are major steps of acid-catalyzed epoxide opening?
epoxide oxygen binds to hydrogen of acid nuc attacks more sub'd carbon which opens ring (if strong acid, it will be deprotonated by the neutral nuc as well)
59
Can RAR occur for acid-catalyzed epoxide opening? ?
No
60
What are stereochemical considerations for acid-catalyzed epoxide opening?
inversion at alpha carbon
61
What is solvent for acid-catalyzed epoxide opening? ?
acid or nuc
62
What type of nuc should NOT be used with strong acid for acid-catalyzed epoxide opening?
anionic nuc (will undergo acid-base chemistry)

Organic Chemistry (26 decks)

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