Synthesis 3

Question 1

What are the 2 mechanisms of nucleophilic substitution

Answer 1

SN1 and SN2

Question 2

Why is it called sn1

Answer 2

As it only has 1 species in the RDS and therefore is first order

Question 3

Why is it called sn2

Answer 3

As it has 2species in the RDS and therefore is second order

Question 4

Describe sn1 mechanism (for this example on haloalkanes)

Answer 4

1. Heterolytic bond fission occurs where the halogen takes both the electrons leaving a carbocation (positively charged carbon) - slow
2. Nucleophile attracted to positive carbocation and donates both electrons to from a bond - fast

Question 5

Describe sn2 mechanism (for this example on haloalkanes)

Answer 5

Five cantered transition state formed where both nucleophile and halogen have a half bond with the carbon. This state has an overall negative charge. This can continue to progress to form new molecule or reverse

Question 6

What is the inductive effect

Answer 6

The increased stability of carbocations due to bulky alkyl groups

Question 7

What is the steric effect

Answer 7

Effect of bulky alkyl groups on nucleophile ( slowing down of reaction as alkyl groups blocks carbon which nucleophile attacks

Question 8

SN1 or SN2 reactions

Answer 8

SN1 - tend to be tertiary and some secondary as they can form stable carbocations
SN2 - tend to be primary and some secondary as they can’t form stable carbocations (SN1=favoured pathway)