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Substitution Reactions Flashcards

1
Q

Substitution Reaction

A

One group is exchanged for another

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2
Q

A substitution reaction can occur when an __________ reacts with an ____________

A

Electrophile, nucleophile

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3
Q

The electrophile is refered to as the _____________ in a substitution reaction

A

Substrate

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4
Q

For an electrophile (a compound with a positive charge or has a partial positive charge) to function as a substrate in a substitution reaction it must contain a ___________

A

Leaving group

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5
Q

What are the two main reasons why the leaving group occurs?

A
  1. The leaving group withdraws electron by induction, rendering the adjacent carbon atom electrophilic
  2. The leaving group can stabilize any negative charge that may develop as the result of the leaving group seperating from the substrate
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6
Q

__________ are common leaving groups

A

Halogens (like Cl, Br, & I)

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7
Q

_____________ organic compounds are commonly used as an electrophile in a substitution reaction

A

Halogenated

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8
Q

The alpha position (⍶)

A

The carbon atom directly connected to the halogen

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9
Q

Beta (β) position

A

Carbon atoms connected to the alpha position

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10
Q

What are the two core steps in a substitution reaction ? (Every substitution reaction will have theses two steps)

A
  1. Nucleophilic attack
  2. Leaving group
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11
Q

In a ___________ reaction nucleophilic attack & loss of the leaving group occurs at the same time

A

Concerted

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12
Q

In a ______________ reaction loss of the leaving group occurs first followed by the nucleophilic attack

A

Stepwise

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13
Q

What is the rate law for SN2 mechanism?

A

R = k [substrate][nucleophile] (Its biomolecular)

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14
Q

What does SN2 stand for ?

A

S- Substitution

N- Nucleophilic

2 - bimolecular

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15
Q

For a SN2 reaction when the alpha position is a chirality center a change in ___________ usually occurs

A

Configuration (If the reactant is (S) then the product will be (R) which is called - Inversion )

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16
Q

For ____________ to occur the nucleophile can only attack from the back side (the side opposite to the leaving group) & never from the front side

A

Inversion

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17
Q

Stereospecific reaction

A

Configuration of the product is dependent on the configuration of the reactant

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18
Q

In an SN2 reaction __________ & ___________ react most quickly with nucleophiles & secondary alkyl halides react more slowly & tertiary alkyl halides are basically unreactive

A

Methyl & primary alkyl halides

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19
Q

The _____________ occurs in the SN2 reaction to form its products

A

Transition State

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20
Q

If the ______________ is high in energy then the Ea will be large & the reaction will be slow

A

Transition State

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21
Q

If the transition state is _________ in energy then the Ea will be small & the reaction will occur fast

A

Low

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22
Q

What are the two core steps in an SN1 reaction ?

A
  1. Loss of the leaving group to form a carbocation intermediate (The rate determining step)
  2. Nucleophilic attack on the carbocation intermediate
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23
Q

For an _______ the energy diagram will have two transition states & ususally the 1st transition state is the rate determing step (have a high Ea)

A

SN1

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24
Q

What is the rate law for a SN1 substitution reaction?

A

R = k[substrate] (The rate only depends on the substrate (electrophile) so increasing or decreasing the concentration of the nucleophile has no effect & its also 1st order) (Its also unimolecular)

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25
What does SN1 stand for?
S- Substitution N- Nucleophile 1- Unimolecular
26
The rate of an SN1 is dependent on the rate at which the ____________ leaves
Leaving group
27
\_\_\_\_\_\_\_\_\_\_\_\_ substrate reacts most quickly & methyl & primary substrates are mostly unreactive in SN1 (opposite of SN2 reaction)
Tertiary
28
Since tertiary are most stable then teritary carbocation will have _________ & secondary carbocation will have \_\_\_\_\_\_\_\_\_
Smaller Ea, Larger Ea
29
Tertiary substrates usually undergo _____ substitution & primary & methyl substrates undergo ______ substitution
SN1, SN2
30
Secondary substrates can undergo _________ substiution reaction & have to look at the nucleophile to decide which one to use
Both
31
\_\_\_\_\_\_\_\_ mechanism is a racemic since it can involve both inverison & rententation of configuration (Carbocation can be attack from either the back or the front)
SN1
32
A concerted reaction is a _______ mechanism
SN2
33
A stepwise reaction is an ______ mechanism
SN1
34
What are the additional steps that can occur in an SN1 mechanism ?
1. Proton transfer before the two core steps 2. A carbocation rearrangement between the two core steps 3. Proton transfer after the two core steps
35
Before the two core steps in an SN1 mechanism a proton transfer is needed whenever the substrate contains an \_\_\_\_\_\_\_\_\_
Alcohol (Hydroxide is a bad leaving group & wont leave by itself, it has to be protonated (gain a hydrogen) to be a good leaving group)
36
After the two core steps of an SN1 mechanism a proton transfer will be needed whenever the nucleophilic is \_\_\_\_\_\_\_\_\_\_\_
Neutral (Has no negative charge)
37
Solvolysis Reactions
Solvent functions as the nucleophilic
38
For a _________________ to occur in an SN1 mechanism the first step (the leaving group) has to generate a carbocation where a methyl or a hydride shift can occur
Carbocation rearrangement
39
What is the additional step that can occur in an SN2 reaction?
A proton transfer before or after the two core steps
40
In an SN2 reaction a proton transfer is needed at the beginning if a substrate is an \_\_\_\_\_\_\_
Alcohol
41
In an SN2 reaction a proton transfer is needed at the end if the \_\_\_\_\_\_\_\_\_\_\_\_\_\_
Nucleophile is neutral
42
What are the four factors that determine if a reaction is SN1 or SN2?
1. The substrate 2. The leaving group 3. The nucleophilic 4. The solvent
43
Methyl & primary substrates favor ___ mechanism & tertiary substrates favors ___ mechanism
SN2, SN1
44
Vinyl halides & Aryl halides are ___________ in substitution reaction
Unreactive
45
Alkyl halides & benzylic halides can also react to __________ mechanisms
Both
46
In the SN2 mechanism it depends on strength & concentration of the nucleophile where it favors a _________ nucleophile
Strong (A strong nucleophile will speed up the reaction & a weak one will slow it down)
47
What are the common strong nucleophiles?
1. I- 2. HS- 3. HO- 4. Br- 5. H2S 6. RO- 7. Cl- 8. RSH 9. NC-
48
What are the common weak nucleophiles?
1. F- 2. H2O 3. ROH
49
A good leaving group is the conjuagted base of a ____________ (is also very stable)
Strong Acid
50
What are some good leaving groups?
1. I 2. Br 3. Cl 4. H2O
51
What are the common leaving groups?
Halides & sulfonate Ions
52
Protic Solvents
Contains at least one hydrogen atom connected directly to an electronegative atom (like water, methanol, ethanol)
53
Polar aprotic solvents
Contains no hydrogen atom connected directly to an electronegative atom (acetated nitrile, acetone, dimethylsulfide (DMSO), or crown ether)
54
Protic solvents are used for _____ mechanisms
SN1
55
Aprotic solvents are used for ___ mechanisms
SN2
56
When selecting reagents for substitution reaction have to consider what?
1. Substrate 2. Nucleophile & Solvent 3. Leaving group
57
Substrate (when selecting a reagent)
The substrate tells us which mechanism is to be used whether SN1 or SN2
58
Nucleophile & solvent (when selecting a reagent)
Have to choose a nucleophile & solvent that favors whatever mechanism is being used (SN1 or SN2)
59
Leaving group (when selecting a reagent)
In an SN1 use an acid to pronate an OH group into an excellent leaving group & for an SN2 an OH is converted into a tosylate (type of sulfonate ion)
60
What are the common halides used as a leaving group?
1. I - 2. Br- 3. Cl-
61
What are the common sulfonate ion used as a leaving group?
1. Tosylate (OTs) 2. Mesylate 3. Triflate
62
What are the seven strong acids ?
1. HI 2. HCl 3. HClO4 4. HBr 5. HNO3 6. H2SO4 7. HClO3
63
Intramolecular substitution reaction
When the nucleophile & electrophile are on the same compound

Organic Chemistry (47 decks)

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