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? Organic Chemistry > 4. Substitution Reactions > Flashcards

4. Substitution Reactions Flashcards

1
Q

what happens in a substitution reaction and when does it occur

A

one group is exchanged for another

occurs when an electrophile is treated with a nucleophile

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2
Q

what is an electrophile known as and what must it contain

A

substrate

contain a good leaving group

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3
Q

what are 3 common leaving groups

A

Br, I, Cl

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4
Q

what are halogenated compounds are used as in substitution reactions

A

electrophiles

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5
Q

what is an alpha carbon

A

carbon atoms connected directly to halogen

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6
Q

what are beta carbons

A

carbons connected to the alpha carbon

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7
Q

what are the 2 mechanisms that occur during a substitution reaction

A

concerted process

stepwise process

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8
Q

what is a concerted process

A

nucleophilic attack and loss of leaving group occur at the same time

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9
Q

what is a stepwise process

A

leaving group is lost first and then the nucleophile attacks

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10
Q

what is the rate equation of an SN2 reactions

A

rate = k[substrate][nucleophile]

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11
Q

what order is the rate equation of SN2 reactions

why

A

second order

rate is linearly dependent on conc of 2 different compounds

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12
Q

is SN2 a concerted process

A

yes

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13
Q

when a SN2 reaction occurs what happens to the configuration

A

inversion of configuration

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14
Q

why does the configuration invert in a SN2 reaction

A

nucleophile can only attack from the side opposite the leaving group

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15
Q

what alkyl halide is most reactive

how does reactivity decrease

A

methyl alkyl halide most reactive

reactivity decreases when moving from primary to secondary to tertiary halides

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16
Q

what is steric hindrance responsible for in reactivity and reaction rate of SN2 reactions and why

A

from extra side chains

decrease in reactivity and reaction rate

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17
Q

why are SN2 reactions slow

A

steric hindrance

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18
Q

why does SN1 reactions likely to occur

A

as SN2 is very slow

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19
Q

what is the rate equation for SN1

A

rate = k[substrate]

20
Q

what is the SN1 reaction rate dependent on

A

only the conc of the substrate

21
Q

will a change in nucleophile conc affect the reaction rate of SN1

A

no

22
Q

for SN1 reaction what are the 2 steps involved and which is the rate determining reaction

A

leaving group leaves first (rate determining step)

nucleophile attacks the carbocation formed

23
Q

what process does SN1 reaction follow

A

stepwise process

24
Q

what is the trend for SN1 compared to SN2

A

trend for SN1 and SN2 reverse of each other

25
Q

what is the substrate that is most reactive for SN1 reactions

A

tertiary substrates most reactive and methyl substrates are least reactive

26
Q

when the leaving group leaves in SN1 reaction what is formed

A

carbocation is formed

27
Q

what kinds of carbocations are most stable

A

tertiary more stable than secondary > primary > methyl alkyl halide

28
Q

what is a planar compound and when is it formed

A

when leaving group of SN1 is eliminated the carbocation (planar compound) is formed

29
Q

what is a planar compound and when is it formed

A

when leaving group of SN1 is eliminated the carbocation (planar compound) is formed

30
Q

does SN1 reactions result in inversion of configuration and why/why not

A

nucleophile has equal chance of attacking from either side of carbocation

some products show retention of configuration and some show inversion of configuration

31
Q

what is a racemic mixture

A

show both R and S configurations

32
Q

what substrates undergo SN1 substitution

A

tertiary substrates

33
Q

what substrates undergo SN2 substitution

A

methyl and primary substrates

34
Q

does secondary substrates undergo SN1 or SN2 reactions

what helps to identify the reation mechanisms

A

SN1 or SN2

look at nucleophiles to help identify reaction mechanisms

35
Q

does strong nucleophiles and weak nucleophiles favor SN1 or SN2

A

strong = SN2

weak = SN1

36
Q

what are the 9 strong nucleophiles

A

I-
Br-
HS-
HO-
H2S
RO-
Cl-
RSH
N(triple bond)C-

37
Q

what are 3 weak nucleophiles

A

F-
H2O
ROH

38
Q

what are protic solvents

A

contain Hydrogen connected to electronegative atom

39
Q

what are polar aprotic solvents

A

contain no H atoms connected to an electronegative atom

40
Q

do protic solvents favour SN1 or SN2

A

SN1 reaction

41
Q

do polar aprotic solvents favour SN1 or SN2

A

SN2

42
Q

what is the rate law for SN1 and SN2

A

SN1 = unimolecular (substrate only)
SN2 = bimolecular (substrate and nucleophile)

43
Q

what is the barrier for SN1 and SN2 reactions

A

SN1 = carbocation stability
SN2 = steric hindrance

44
Q

what is the order of reactivity of alkyl halides for SN1 and SN2 reactions

A

SN1 = 3 > 2&raquo_space; 1
SN2 = 1 > 2&raquo_space; 3

45
Q

what is the nucleophile characteristics for SN1 and SN2 reactions in terms of strength

A

SN1 = weak (generally neutral)
SN2 = strong (generally bearing a negative charge)

46
Q

what is the solvent characteristic like for SN1 and SN2 reactions in terms of protic

A

SN1 = protic
SN2 = polar aprotic

47
Q

what is the stereochemistry of compounds resulting from SN1 and SN2 reactions

A

SN1 = retention and inversion
SN2 = inversion

? Organic Chemistry (16 decks)

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