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Organic Chemistry > Substitution + Elimination > Flashcards

Substitution + Elimination Flashcards

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1
Q

Sn1

A

unimolecular

occurs on sp3 substrate -> form stabilised C+ intermediate

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2
Q

Sn1 - stereochemistry

A

racemic

due to planar C+

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3
Q

Sn1 - solvent

A

[polar protic]

transition state/intermediate = more polar than neutral starting material

polar protic solvent stabilises both C+ and anion from cleavage of C-X bond

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4
Q

Sn2

A

bimolecular

occurs on unhindered sp3 electrophilic centres

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5
Q

Sn2 - stereochemistry

A

inversion

Nu approaches @ 180 degrees

trigonal bipyramidal transition state

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6
Q

Sn2 - solvent

A

[polar aprotic]

no C+ that needs stabilising

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7
Q

what makes a good leaving group?

A

c. base of strong acid (forms stable anion)

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8
Q

are alcohols are a good leaving group?

A

no - must be activated

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9
Q

how are alcohols activated?

A
  1. protonation
  2. sulfonate ester formation
  3. alkyl chloride formation
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10
Q

rules for reactivity of nucleophiles

A
  1. anionic Nu > neutral Nu
  2. for Nu on same atom, anions that are c. base of weak acids = better Nu
  3. Nu based on atoms lower down periodic table = more reactive
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11
Q

examples of good Nu

A

[alkoxide] RO-

[thiolate] RS-

[bromide] Br-

[iodide] I-

[axide] N3-

[cyanide] NC-

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12
Q

E1

A

unimolecular

sp3 substrates that can form stabilised carbocation intermediate with good leaving group

β hydrogen needed

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13
Q

what type of base is usually used for E1 reactions?

A

weak bases

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14
Q

what temp. is favoured for E1 reactions?

A

high

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15
Q

E1 - stereoselectivity

A

least hindered conformation of carbocation

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16
Q

E1 - regioselectivity

A

formation of more sub. alkene

thermodynamically + kinetically favoured

17
Q

E2

A

bimolecular

sp3 substrate with good leaving group + β-hydrogen (must be periplanar to maximise orbital overlap)

18
Q

what type of base is usually used for E2 reactions?

A

strong bases

19
Q

when there is a choice of β-hydrogens - which route is favoured?

A

least hindered anti-periplanar conformation

with 1 β-hydrogen = stereoSPECIFIC

20
Q

E2 - regioselectivity

A

large bases = less sub alkene (Hofmann)

small bases = more sub. alkene (Saytsev)

Organic Chemistry (13 decks)

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