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Chemistry 101 COPY > Substitution Reactions (SN1) > Flashcards

Substitution Reactions (SN1) Flashcards

1
Q

What is the physical result of a stepwise substitution reaction?

A

Racemisation

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2
Q

Which nucleophiles will increase the reaction rate of an SN2 reaction?

A

A good nucleophile (strong base)

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3
Q

What are carbocations?

A

Compounds where one carbon has lost an electron and thus has a positive charge

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4
Q

How do you determine the rate determining step from an energy profile?

A

The highest transition state.

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5
Q

How many alkyl substituents does a primary carbocation have?

A

One

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6
Q

Why do alkyl groups increase the stability of the carbocation?

A

As they donate electrons through a sigma bond to the positively charged carbon, decreasing the positive charge, making it more stable

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7
Q

Are SN1 reactions unimolecular or bimolecular?

A

Unimolcular

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8
Q

What effect do polar aprotic solvents have on cations?

A

They stabilise them

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9
Q

Which alkyl halide structure reacts the fastest in SN2 reactions?

A

Methyl alkyl halides

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10
Q

What are polar aprotic substances?

A

Polar solvents without an OH group

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11
Q

What can be said about the energy profile of a two-step process?

A

It has two transition states.

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12
Q

Are carbocations chiral?

A

No, they are achiral

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13
Q

What occurs to the stereochemistry of the substrate in an SN1 reaction?

A

A racemic mixture is formed through planar carbocation

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14
Q

Why does the strength of the nucleophile not affect the rate of reaction in a stepwise mechanism?

A

As the nucleophile is not involved in the rate determining step.

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15
Q

Describe the leaving group of an SN1 reaction

A

A stable anion

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16
Q

What are carbocations classified according to?

A

The number of alkyl substituents bonded to the positively charged carbon.

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17
Q

What do polar protic solvents have?

A

An OH group

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18
Q

What is the donation of electrons through the bond referred to as?

A

Induction

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19
Q

What are the two types of solvents that can affect which reaction occurs?

A

Polar protic substances Polar aprotic substances

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20
Q

What do polar protic substances do to the reaction rate of SN2 reactions?

A

Slow down the rate of SN2

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21
Q

What does the stability of a carbocation increase with?

A

The number of alkyl groups.

22
Q

Which nucleophiles will increase the reaction rate of an SN1 reaction?

A

It doesn’t matter as the nucleophile is not involved in the rate limiting step

23
Q

How many alkyl substituents does a tertiary carbocation have?

A

Three

24
Q

How many alkyl substituents does a secondary carbocation have?

A

Two

25
Q

What does the stability of a carbocation depend on?

A

What is attached to the carbon with the positive charge.

26
Q

What is a stepwise process?

A

Where the loss of a leaving group occurs first, followed by nucleophilic attack.

27
Q

What effect do polar aprotic solvents have on anions?

A

They have no effect on anions

28
Q

How many “steps” does an SN1 reaction have?

A

Two

29
Q

What occurs to the stereochemistry of the substrate in an SN2 reaction?

A

Stereocentre inversion

30
Q

How does the stability of the carbocation affect the reaction rate?

A

The more stable the transition state, the smaller the activation energy is, and therefore, the faster is the reaction

31
Q

How do polar protic substances affect the reaction rate?

A

They form hydrogen bonds with the negative charges, solvating the nucleophile, slowing the rate of SN2

32
Q

What is racemisation?

A

Where you go from 100% of either R or S to 50% of each

33
Q

Which alkyl halide structure reacts the fastest in SN1 reactions?

A

Tertiary alkyl halides

34
Q

What makes a stepwise mechanism faster?

A

A good leaving group

35
Q

What is the molecular geometry of carbocations?

A

They are planar

36
Q

What is significant about carbocations being planar?

A

A nucleophile can attack from either side.

37
Q

What is a concerted process?

A

Where nucleophilic attack and the loss of a leaving group occur simultaneously

38
Q

How many “steps” does an SN2 reaction have?

A

One

39
Q

What is the rate law for an SN2 reaction?

A

Rate=k[alkyl halide][nucleophile]

40
Q

Give three examples of good nucleophiles (strong bases)

A

Br- OH- CH3O-

41
Q

What is the rate law for an SN1 reaction?

A

Rate=k[alkyl halide]

42
Q

Describe the leaving group of an SN2 reaction

A

A stable anion

43
Q

When are carbocations formed?

A

when a leaving group steals the two electrons from a covalent bond

44
Q

What is the hybridisation of carbocations?

A

sp2

45
Q

What is the order of speed of reaction of stepwise process by the order of the alkyl substrate?

A

Tertiary>Secondary>Primary

46
Q

Does the concentatrion of the nucleophile affect the rate of reaction in a stepwise process?

A

No

47
Q

What is the rate of reaction in a stepwise process dependent on?

A

Only the concentration of the substrate.

48
Q

What are stepwise substitution reactions also called?

A

SN1

49
Q

Why does a good leaving group make a stepwise mechanism faster?

A

Because the substrate (which has the leaving group) is a part of the rate determining step.

50
Q

What do polar protic substances do to the reaction rate of SN1 reactions?

A

Speed up the rate of SN1

51
Q

How many alkyl substituents does a methyl carbocation have?

A

None

Chemistry 101 COPY (32 decks)

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