Chapter 13.4 - Electrophilic addition in alkenes

Question 1

What is an electrophile?

Answer 1

An atom or group of atoms that is attracted to an electron rich centre and accepts an electron pair

Question 2

Show the reaction mechanism of the reaction between but-2-ene and hydrogen bromide

Answer 2

:)
- Dipoles
- Carbocation intermediate + halide electrons and charge
- End product(s)

Question 3

Show the reaction mechanism of the reaction between propene and bromine

Answer 3

:)
- Dipoles
- Carbocation intermediate + halide electrons and charge
- End product(s)

Question 4

Why is bromine polar?

Answer 4

• The bonding pair of electrons are distributed equally between the two atoms
• As bromine approached the pi bond, the electron density caused the electrons in the bromine to be repelled
• Polarity has been induced

Question 5

What is the difference between primary, secondary, and tertiary carbocations?

Answer 5

Primary - One alkyl group, two hydrogens
Secondary - Two alkyl groups, one hydrogen
Tertiary - Three alkyl groups, no hydrogens

Question 6

Describe the pattern of carbocation stability

Answer 6

• Stability increases with the more alkyl groups in carbocations
• This is because the positive charge is spread over the alkyl groups
• The more alkyl groups, the greater spread of charge, making the ion more stable (inductive effect)
• So the carbocation with the more alkyl groups will be the major product
• tertiary>secondary>primary (stability)