Synthesis 6

Question 1

Describe Electrophilic addition mechanism ( in this example halogen halide - HBr)

Answer 1

1. C~C double bond breaks and the pair of electrons attaches to slight positive H
   H~Br breaks so Br takes both electrons
   A carbocation is formed
2. The Br becomes a nucleophile and attacks carbocation

Question 2

How can Br act as a electrophile

Answer 2

The electrons in the alkenes double bond repels the electron pair so can shift them closer to one Br molecule = inducing a dipole

Question 3

According to markovnikov how can carbocation stability increase

Answer 3

By increasing substitution by carbon

Tertiary > secondary > primary > methyl

Question 4

In the addition to unsymmetrical alkenes 2 products can be formed, how do you know which will be favoured

Answer 4

The pathway that forms the most stable carbocation tertiary > secondary
remember markovnikovs

Question 5

Describe the mechanism of the hydrogenation of alkenes

Answer 5

Use of Nickel or platinum catalyst
Hydrogen is absorbed onto catalyst is breaking H2 into 2x H
The pi - bonds from alkene bond to catalyst surface
The hydrogen atoms then bond to alkene
With no pi- bond new alkane leaves catalyst

Question 6

Acid catalysed hydration mechanism

Answer 6

1. The H+ ion of the acid catalyst acts as electrophile and attacks double bond
2. Carbocation intermediate immediately undergoes nucleophilic attack by water
3. Protanated alcohol is a strong acid and easily loses a proton to form final alcohol