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CHEM333 (RBL) > 3. SN1/ SN2 Revision > Flashcards

3. SN1/ SN2 Revision Flashcards

1
Q

What is the rate equation for SN2 reactions?

A

rate = k[Nu][RX]

SN2 reactions involve a bimolecular mechanism where the rate depends on both the nucleophile and the substrate.

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2
Q

What types of substrates are favored in SN2 reactions?

A

1°, 2°

SN2 reactions are most effective with primary and secondary substrates due to steric hindrance.

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3
Q

What is the impact of steric hindrance on SN2 reactions?

A

Hindered slow

Steric hindrance can slow down SN2 reactions, making them less favorable.

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4
Q

What is the nucleophilicity order in polar protic solvents like MeOH?

A

PhS’ > HO- > FEN > CN > NH,OH > NH > RO* > NH, N > PhO > Br > PHSH > PhNH > pyridine > Cl > ACO- > F- > SO- > NO, ROH

The nucleophilicity order indicates the relative strength of nucleophiles in a polar protic environment.

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5
Q

What is the rate equation for SN1 reactions?

A

rate = K[RX]

SN1 reactions follow a unimolecular mechanism, where the rate depends solely on the substrate.

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6
Q

What types of substrates are favored in SN1 reactions?

A

2°, 3°

SN1 reactions are favored by secondary and tertiary substrates due to the stability of the carbocation intermediate.

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7
Q

What factor does not affect the rate of SN1 reactions?

A

Doesn’t matter

The nucleophile’s strength does not influence the rate of SN1 reactions.

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8
Q

What is the significance of leaving groups in both SN1 and SN2 reactions?

A

Need reasonable, need good

The ability of a leaving group to depart is crucial for the success of both SN1 and SN2 mechanisms.

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9
Q

Fill in the blank: The nucleophile in an SN2 reaction must have a _______ charge for effective reaction.

A

reasonable

A reasonable charge on the nucleophile enhances its reactivity in SN2 reactions.

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10
Q

What is the role of charge distribution in SN1 reactions?

A

Charge spread over benzene ring

In SN1 reactions, the charge can be stabilized through resonance in aromatic systems.

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11
Q

True or False: A larger nucleophile generally has better leaving group ability.

A

False

Larger nucleophiles may not have better leaving group ability; the quality of leaving groups varies independently.

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12
Q

What is the definition of E1cb?

A

E1cb mechanism

E1cb refers to a mechanism where a leaving group is expelled after proton abstraction, leading to an elimination reaction.

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13
Q

What does SN2 stand for?

A

Substitution Nucleophilic Bimolecular

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14
Q

What is the main characteristic of SN2 reactions?

A

Bimolecular mechanism involving two reactants

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15
Q

In SN2 reactions, how does the solvent affect the reaction rate?

A

Polar aprotic solvents increase reactivity

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16
Q

Fill in the blank: In polar protic solvents, _______ are solvated.

A

anions

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17
Q

List the halide reactivity in SN2 reactions from most to least reactive.

A
  • F
  • Br
  • Cl
18
Q

What is the role of KReL in hydrolysis?

A

Catalyst in nucleophilic substitution reactions

19
Q

What type of solvent is best for SN1 reactions?

A

Polar protic solvents

20
Q

True or False: SN1 reactions are unimolecular.

A

True

21
Q

What is the effect of a polar aprotic solvent on anions in SN2 reactions?

A

Anions are still solvated but more reactive

22
Q

What does the ‘Br’ symbol refer to in the context of nucleophilic substitution?

A

Bromide ion

23
Q

What is the significance of DMSO and DMF in SN2 reactions?

A

They are polar aprotic solvents that enhance nucleophilicity

24
Q

Fill in the blank: The formula for a common polar protic solvent is _______.

A

H2O

25
Q

In the context of nucleophilic substitution, what does ‘Me’ refer to?

A

Methyl group

26
Q

What is the general trend in reactivity for halides in SN2 reactions?

A

Reactivity decreases from F to Cl

27
Q

What does ‘H-OR’ represent in the context of solvents?

A

Alcohols used as polar protic solvents

28
Q

What is the primary difference between SN1 and SN2 mechanisms?

A

SN1 is unimolecular; SN2 is bimolecular

29
Q

True or False: SN2 reactions typically involve a transition state.

A

True

30
Q

What type of reaction mechanism does the ‘106’ refer to?

A

Rate constant for a specific reaction

31
Q

What is the mechanism of the SN2 reaction?

A

A bimolecular nucleophilic substitution reaction where the nucleophile attacks the substrate simultaneously as the leaving group departs

This results in inversion of configuration at the carbon center.

32
Q

What is the primary characteristic of the SN1 reaction?

A

A unimolecular nucleophilic substitution reaction that proceeds through a carbocation intermediate

The reaction occurs in two steps: formation of the carbocation and then nucleophilic attack.

33
Q

What does ‘contact ion pair’ refer to?

A

A pair of ions that are in close proximity but not fully separated in solution

This occurs in the context of SN1 reactions.

34
Q

Define ‘solvent separated ion pair’.

A

An ion pair that is separated by solvent molecules, allowing for greater mobility of the ions

This is relevant in the context of SN1 mechanisms.

35
Q

What is a ‘free ion pair’?

A

An ion pair where the ions are fully separated and free to move in solution

This can influence the reactivity in nucleophilic substitutions.

36
Q

What is the outcome of an SN2 reaction in terms of stereochemistry?

A

Mainly inversion of configuration at the carbon center

This is due to the backside attack mechanism of the nucleophile.

37
Q

What is the stereochemical outcome of an SN1 reaction?

A

50% inversion and 50% retention of configuration

This can lead to racemization if the substrate is chiral.

38
Q

In which type of reaction is racemization most likely to occur?

A

SN1 reaction

Racemization occurs if the substrate is chiral and allows both enantiomers to form.

39
Q

In the context of SN2 reactions, what does ‘Nu’ represent?

A

Nucleophile

The nucleophile is the species that donates an electron pair in the reaction.

40
Q

What does the notation ‘R1, R2, R3’ typically indicate?

A

Different substituents on the carbon atom involved in the nucleophilic substitution

These represent varying groups attached to the substrate.

41
Q

Fill in the blank: In an SN1 reaction, the nucleophile attacks after the formation of a _______.

A

carbocation

CHEM333 (RBL) (7 decks)

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