3.3.4.2 Addition reactions of alkenes

Question 1

What type of molecules make good electrophiles?

Answer 1

Polar molecules e.g. H-Br.
The delta+ on the H is electron deficient, so attracted to the high electron density double bond.
Neutral molecules can be induced to have a dipole, so can also act as electrophiles.

Question 2

What are the types of electrophiles for alkenes? (that are covered in AS)

Answer 2

Hydrogen halides
Asymmetrical addition
Concentrated sulfuric acid
Neutral electrophiles (Br2)

Question 3

What is the product formed when alkenes undergo electrophilic addition with hydrogen halides?

Answer 3

Halogenoalkanes

Question 4

What are the three types of carbocations?

Answer 4

Primary
Secondary
Tertiary

Question 5

Describe the positive inductive effect

Answer 5

Alkyl groups are electron donating compared to hydrogen atoms.
Electrons from alkyl groups are ‘released’ towards carbocation, so size of the carbocation decreases it leads to the stabilisation of the carbocation intermediate.
So the more alkyl groups, the more stable it is

Question 6

What is the product formed when undergoing electrophilic addition with concentrated sulfuric acid?

Answer 6

Sulfuric acid is a polar electrophile
Alkyl hydrogen sulfate

Question 7

What is the product formed when undergoing electrophilic addition with neutral electrophiles?

Answer 7

Dihalogenoalkane