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MCAT chem > organic reaction mechanism > Flashcards

organic reaction mechanism Flashcards

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1
Q

electrophiles

A

species that want electrons
- often positive charges

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2
Q

nucleophiles

A

have excess of electrons

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3
Q

SN1

A

unimolecular nucleophilic subsitution reaction
two step mechanism
carbocation intermediate

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4
Q

nucleophilic substitution

A

nucleophile attacks electrophile
- nucleophile replaces the leaving group as a new substituent on the electrophile

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5
Q

how to identify the nucleophile

A

has one or more lone pairs and excess electrons

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6
Q

how to identify electrophile

A

partial or full positive charge that wants to accept elecrons

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7
Q

leaving group

A

typically a weak base, that will break its bond with the electrophile after nucleophilic attack with nucleophile

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8
Q

common leaving groups

A

Br- , cl- , I-, Oh-. R3N

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9
Q

general mechanism of nucleophilic SN1 reaction

A
  1. the nucleophilic attack
  2. transfer of e- to LG
  3. LG leaves
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10
Q

two major types of nucleophilic substitutions SN1 and SN2

A

sn1 and sn2
1 and 2 are based on the rate laws of the reaction

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11
Q

sn1 rate law is dependent on

A

the concentration of the substrate

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12
Q

sn2 rate law dependent on

A

the concentration of substrate and nucleophile

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13
Q

sn1 mechanism

A
  1. leaving group leaves first
  2. carbocation forms (unstable)
  3. nu attack
  4. nu deprotinated
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14
Q

rate limiting step of sn1 rxn

A

the carbocation formation
- very slow

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15
Q

how to enhance carbocation stability

A
  1. make carbocation more substituted
    terciary carbocations> secondary> primary
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16
Q

is sn1 racemic

A

yes, produces 50/50 mix

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17
Q

sn2

A

backside attack and inversion of steriochemistry
tranition state includes nu bond forming and LG breaking

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18
Q

favor sn2

A

strong nu (OH-)
not sterically hindered primary> secondary >tert

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19
Q

polar protic solvents

A

hydrogen atoms attatched to polar molecule, water, etoh, meoh

20
Q

polar aprotic solvent

A

c=o but no hydrogen in polar molecule ex: acetone and dmso

21
Q

which nucleophilic reaction is favored by polar protic solvents, why

A

sn1 because it is able to hydrogen bond and stabilize the carbocation

22
Q

which nucleophilic reactionis facored by polar aprotic solvents

A

sn2

23
Q

what is the key to the sn2 mechanism

A

steric hindreance

24
Q

rate law of sn2

A

depends on concentration of substrate and nu

25
Q

strengh of nu in sn1

A

doesnt matter

26
Q

strength of nu in sn2

A

strong and nonbulky

27
Q

steriochemistry of sn2

A

inverted bc of backside attack

28
Q

nucleophilic elimination

A

lg is kicked out and replaced with a double bond
can also be E1 and E2

29
Q

E1 mechanism

A

similar to SN1 mechanism
- unimolecular rate law driven by carbocation formation
- nu pulls off e- from adjacent c
form double bond
1. LG leaves and C+ form
2. nu pulls hydrogen and form db

30
Q

E2 mechanism

A

bimolecular rate law
strong base attacks electrophilic hydrogen and leaving group leave at same time

31
Q

Zaitsev rule

A

the double bond formed is more substituted

32
Q

fisher esterification

A

acid catalyzed conversion of COOH into an ester
COOH +ROH in presence of acid

33
Q

fisher esterification mechanism

A
  1. protination of carbonyl oxygen with acid
  2. oxygen of alochol attack electrophilic carbonyl carbon
  3. protinate OH group
  4. then carnboyl carbon does electrophilic attack and removes h2o leaving group
  5. water deprotinates carbonyl oxygen
34
Q

how is fischer esterification reversed

A

hydrolysis
OR group is leaving group and OH attacks and reforms subsitutent to form COOH and ROH

35
Q

imine formation

A

nucleophilic substitution with NH3 group or NH2R or NHR2
c=n replaces c=o

36
Q

shiff base

A

imine with a carbon substitioent

37
Q

imine formation mechanism

A
  1. protinate the cabronyl oxygen
  2. amine group attacks carbonyl C
  3. proton transfer from n to O to make h2o grup
  4. N attacks cabtonul and h2o leaves
  5. n group is deprotinated by wter
38
Q

what happens to a ketone if it undergoes nucleophilic addition

A

hemiketal formation

39
Q

tautomerization

A

two structures interconvert at equilibrium
not resonance

40
Q

keto - enol tautomerization

A

keto and enol forms c=o and c=c
acid and basic mechanisms

41
Q

requitement for enol tautomer

A

at least one hydrogen on the adjacent alpha carbon

42
Q

enolate

A

keto-enol intermediate with neg charge acts as a nuclephile

43
Q

enolate formation can be catalyzed

A

by acids and bases

44
Q

micheal addition

A

a, b unsaturated aldehydes or ketones generated
aldehyde attacks double bond and forms an a, b unsaturated aldehyde

45
Q

robinson annulation

A

micheal addition followed by aldol condensation so it becomes ciclical and one of the aldehydes becaomes an oh

46
Q

aldol condensation

A

nucleophilic alpha carbon attack on electrophilic carbon to form new c-c bond

47
Q

retro aldol

A

reverse aldol condensation reaction

MCAT chem (11 decks)

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