free radicals substitution propgation

Question 1

first step

The propagation step refers to the progression (…………..) of the substitution reaction in a chain reaction

Free radicals are very reactive and will ……….

Answer 1

growing

attack the unreactive alkanes

Question 2

When free radicals attack what bond is broken

and what is produced

Answer 2

A C-H bond breaks homolytically (each atom gets an electron from the covalent bond)

An alkyl free radical is produced

Question 3

third step

alkyl free radical is produced

This can attack another ……………… molecule to form the halogenoalkane and regenerate the …………………….

Answer 3

chlorine/bromine

chlorine/bromine free radical

This free radical can then repeat the cycle

Question 4

The second step of the free-radical substitution reaction is the propagation step in which the reaction grows in a chain reaction

This reaction is not very suitable for preparing specific halogenoalkanes as

Answer 4

a mixture of substitution products are formed
If there is enough chlorine/bromine present, all the hydrogens in the alkane will eventually get substituted (eg. ethane will become C2Cl6/C2Br6)