Chapter 9.2: Mechanisms of Nucleophilic Aliphatic Substitution

Question 1

Define bimolecular reaction

Answer 1

a reaction in which two species are involved in the rate-determining step

Question 2

What is the stereochemistry of the Sn1 reaction?

Answer 2

o Stereochemistry: stereochemistry is scrambled (not 1:1 exactly)

Question 3

What is a reaction in which only one species is involved in the rate-determining step?

Answer 3

unimolecular reaction

Question 4

Why is the Sn1 reaction unimolecular?

Answer 4

 Only the haloalkane is involved in the rate-determining step

Question 5

When is the Sn2 mechanism preferred? (steric hindrance and carbocation stability)

Answer 5

o Favored when steric hinderance is low or carbocation stability is low

Question 6

What is a nucleophilic substitution in which the solvent is also the nucleophile?

Answer 6

solvolysis

Question 7

What is a reaction in which two species are involved in the rate-determining step?

Answer 7

bimolecular reaction

Question 8

Define solvolysis

Answer 8

a nucleophilic substitution in which the solvent is also the nucleophile

Question 9

Define Sn2 reaction

Answer 9

a bimolecular nucleophilic substitution reaction

Question 10

What is a unimolecular nucleophilic substitution reaction?

Answer 10

Sn1 reaction

Question 11

Define unimolecular reaction

Answer 11

a reaction in which only one species is involved in the rate-determining step

Question 12

What is the stereochemistry of the Sn2 mechanism?

Answer 12

o Stereochemistry: inversion at site of reaction

Question 13

Describe the Sn1 mechanism

Answer 13

 Step 1: Break a bond to give stable molecules or ions
• Formation of a carbocation intermediate. Because no nucleophile is assisting the departure of the halide anion, this is the relatively slow, rate-determining step of the reaction.
 Step 2: Make a new bond between a nucleophile and an electrophile
 Step 3: Take a proton away

Question 14

What is a bimolecular nucleophilic substitution reaction?

Answer 14

Sn2 reaction

Question 15

Define Sn1 reaction

Answer 15

a unimolecular nucleophilic substitution reaction

Question 16

Describe the Sn2 mechanism

Answer 16

 Make a new bond between a nucleophile and an electrophile and simultaneously break a bond to give stable molecules or ions
• The nucleophile attacks the reactive center from the side opposite the leaving group; involves backside attack of the nucleophile

Question 17

Why is the Sn2 mechanism bimolecular?

Answer 17

• Both the haloalkane and nucleophile are involved in the rate-determining step

Question 18

When is the Sn1 mechanism preferred? (steric hindrance and carbocation stability)

Answer 18

o Favored when steric hindrance is high or carbocation stability is high