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Organic Chemistry > Substitution Reactions > Flashcards

Substitution Reactions Flashcards

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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
Q

What does SN1 stand for?

A

S- Substitution

N- Nucleophile

1- Unimolecular

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26
Q

The rate of an SN1 is dependent on the rate at which the ____________ leaves

A

Leaving group

27
Q

____________ substrate reacts most quickly & methyl & primary substrates are mostly unreactive in SN1 (opposite of SN2 reaction)

A

Tertiary

28
Q

Since tertiary are most stable then teritary carbocation will have _________ & secondary carbocation will have _________

A

Smaller Ea, Larger Ea

29
Q

Tertiary substrates usually undergo _____ substitution & primary & methyl substrates undergo ______ substitution

A

SN1, SN2

30
Q

Secondary substrates can undergo _________ substiution reaction & have to look at the nucleophile to decide which one to use

A

Both

31
Q

________ mechanism is a racemic since it can involve both inverison & rententation of configuration (Carbocation can be attack from either the back or the front)

A

SN1

32
Q

A concerted reaction is a _______ mechanism

A

SN2

33
Q

A stepwise reaction is an ______ mechanism

A

SN1

34
Q

What are the additional steps that can occur in an SN1 mechanism ?

A
  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
Q

Before the two core steps in an SN1 mechanism a proton transfer is needed whenever the substrate contains an _________

A

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
Q

After the two core steps of an SN1 mechanism a proton transfer will be needed whenever the nucleophilic is ___________

A

Neutral (Has no negative charge)

37
Q

Solvolysis Reactions

A

Solvent functions as the nucleophilic

38
Q

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

A

Carbocation rearrangement

39
Q

What is the additional step that can occur in an SN2 reaction?

A

A proton transfer before or after the two core steps

40
Q

In an SN2 reaction a proton transfer is needed at the beginning if a substrate is an _______

A

Alcohol

41
Q

In an SN2 reaction a proton transfer is needed at the end if the ______________

A

Nucleophile is neutral

42
Q

What are the four factors that determine if a reaction is SN1 or SN2?

A
  1. The substrate
  2. The leaving group
  3. The nucleophilic
  4. The solvent
43
Q

Methyl & primary substrates favor ___ mechanism & tertiary substrates favors ___ mechanism

A

SN2, SN1

44
Q

Vinyl halides & Aryl halides are ___________ in substitution reaction

A

Unreactive

45
Q

Alkyl halides & benzylic halides can also react to __________ mechanisms

A

Both

46
Q

In the SN2 mechanism it depends on strength & concentration of the nucleophile where it favors a _________ nucleophile

A

Strong (A strong nucleophile will speed up the reaction & a weak one will slow it down)

47
Q

What are the common strong nucleophiles?

A
  1. I-
  2. HS-
  3. HO-
  4. Br-
  5. H2S
  6. RO-
  7. Cl-
  8. RSH
  9. NC-
48
Q

What are the common weak nucleophiles?

A
  1. F-
  2. H2O
  3. ROH
49
Q

A good leaving group is the conjuagted base of a ____________ (is also very stable)

A

Strong Acid

50
Q

What are some good leaving groups?

A
  1. I
  2. Br
  3. Cl
  4. H2O
51
Q

What are the common leaving groups?

A

Halides & sulfonate Ions

52
Q

Protic Solvents

A

Contains at least one hydrogen atom connected directly to an electronegative atom (like water, methanol, ethanol)

53
Q

Polar aprotic solvents

A

Contains no hydrogen atom connected directly to an electronegative atom (acetated nitrile, acetone, dimethylsulfide (DMSO), or crown ether)

54
Q

Protic solvents are used for _____ mechanisms

A

SN1

55
Q

Aprotic solvents are used for ___ mechanisms

A

SN2

56
Q

When selecting reagents for substitution reaction have to consider what?

A
  1. Substrate
  2. Nucleophile & Solvent
  3. Leaving group
57
Q

Substrate (when selecting a reagent)

A

The substrate tells us which mechanism is to be used whether SN1 or SN2

58
Q

Nucleophile & solvent (when selecting a reagent)

A

Have to choose a nucleophile & solvent that favors whatever mechanism is being used (SN1 or SN2)

59
Q

Leaving group (when selecting a reagent)

A

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
Q

What are the common halides used as a leaving group?

A
  1. I -
  2. Br-
  3. Cl-
61
Q

What are the common sulfonate ion used as a leaving group?

A
  1. Tosylate (OTs)
  2. Mesylate
  3. Triflate
62
Q

What are the seven strong acids ?

A
  1. HI
  2. HCl
  3. HClO4
  4. HBr
  5. HNO3
  6. H2SO4
  7. HClO3
63
Q

Intramolecular substitution reaction

A

When the nucleophile & electrophile are on the same compound

Organic Chemistry (47 decks)

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