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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
Q

What is solvent for chlorodehydration with SOCl2 (alkyl chloride synthesis)?

A

amine base (polar / aprotic)

26
Q

What are SM and P of bromodehydration with PBr3 (alkyl bromide synthesis)?

A 
SM = 1º or 2º alcohol only
P = alkyl bromide
27
Q

What are reagents of for bromodehydration with PBr3 (alkyl bromide synthesis)?

A

PBr3 and pyridine (or Br-)

28
Q

What type of mechanism is bromodehydration with PBr3 (alkyl bromide synthesis)?

A

Sn2 only! so NR for 3º alcohols

29
Q

What are major steps of bromodehydration with PBr3 (alkyl bromide synthesis)?

A

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
Q

Can RAR occur for bromodehydration with PBr3 (alkyl bromide synthesis)?

A

No, Sn2 so no carbocations form

31
Q

What stereochemical considerations are there for bromodehydration with PBr3 (alkyl bromide synthesis)?

A

Sn2 rules so inversion at alpha carbon if st. center

32
Q

What is solvent for bromodehydration with PBr3 (alkyl bromide synthesis)?

A

amine base

33
Q

What is tosylate?

A

derivative of alcohol that is THE BEST LG!!

34
Q

How are alcohols converted to tosylates?

A

Tosylation with TsCl

35
Q

Why is tosylate a good LG?

A

because its conjugate acid is tosic acid which is strong (pKa = -7)

36
Q

Why are alkyl tosylates called the “middle man”?

A

they are rarely the final product of synthesis, usually they are a synthetic intermediate

37
Q

Is alpha carbon electrophilic when bonded to OH?

A

No, only when OH becomes good LG

38
Q

What are SM and P for tosylation with TsCl?

A 
SM = alcohol (any sub, Csp3 not required)
P = alkyl tosylate
39
Q

What are reagents of tosylation with TsCl?

A

TsCl and pyridine

40
Q

What type of mechanism is tosylation with TsCl?

A

oxygen binds to Ts and kicks off Cl… not Sn2 (but can go under Sn2 after it becomes alkyl tosylate)

41
Q

What are major steps of tosylation with TsCl?

A

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
Q

Can RAR occur or tosylation with TsCl?

A

No, not a chance for carbocations

43
Q

What are the stereochemical considerations for tosylation with TsCl?

A

NO inversion at alpha carbon because reaction takes place at hydroxyl carbon

inversion only occurs if alkyl tosylate undergoes Sn2 afterwards

44
Q

What is solvent for tosylation with TsCl?

A

polar aprotic

45
Q

Do epoxides have a good LG? Why are they reactive?

A

No good LG but they are highly strained with 2 polar bonds so they are pretty reactive (ring-opening is favored)

46
Q

What are five nucs that can open an epoxide ring?

A

-OH, -OR, -CN, -SR, NH3

47
Q

What is SM and P of nucleophilic epoxide opening?

A 
SM = epoxide
P = alcohol
48
Q

What are reagents of nucleophilic epoxide opening?

A

strong anionic nucleophile and H2O

49
Q

Why is nucleophilic epoxide opening considered to be a regioselective reaction?

A

nuc only attacks at less sterically hindered carbon

50
Q

What type of mechanism is nucleophilic epoxide opening?

A

Sn2

51
Q

What are major steps of nucleophilic epoxide opening?

A

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
Q

Can RAR occur for nucleophilic epoxide opening?

A

No, Sn2

53
Q

What are stereochemical considerations for nucleophilic epoxide opening?

A

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
Q

What is solvent for nucleophilic epoxide opening?

A

polar aprotic

55
Q

What are SM and P of acid-catalyzed epoxide opening?

A 
SM = epoxide
P = alcohol
56
Q

What are reagents of acid-catalyzed epoxide opening?

A

HX and Nu-H
or
strong acid (TsOH and H2So4) and neutral nuc

57
Q

What is mechanism of acid-catalyzed epoxide opening?

A

Sn2-like

58
Q

What are major steps of acid-catalyzed epoxide opening?

A

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
Q

Can RAR occur for acid-catalyzed epoxide opening? ?

A

No

60
Q

What are stereochemical considerations for acid-catalyzed epoxide opening?

A

inversion at alpha carbon

61
Q

What is solvent for acid-catalyzed epoxide opening? ?

A

acid or nuc

62
Q

What type of nuc should NOT be used with strong acid for acid-catalyzed epoxide opening?

A

anionic nuc (will undergo acid-base chemistry)

Organic Chemistry (26 decks)

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