Mechanism 1: Radical substitution

Question 1

alkane + halogens —>

Answer 1

haloalkanes

Question 2

what must be present for alkanes and halogens to react?

Answer 2

UV light

Question 3

how are free radicals shown?

Answer 3

single dot

Question 4

what does the UV light do?

Answer 4

the UV breaks down the halogen bonds (homolytic fission), producing free radicals, these then attack the alkanes

Question 5

what are the three steps of radical susbtitution?

Answer 5

initiation, propagation and termination

Question 6

what happens in the initiation step? use Cl2

Answer 6

the halogen halogen bond is broken to form 2 free radicals

 UV Cl2---> 2Cl*

Question 7

what happens in the propagation step? use Cl2 and CH4

Answer 7

molecule + radical—> diff molecule and diff radical
CH4 + Cl*—> *CH3 + HCl
CH3+ Cl2 —> CH3Cl + Cl

Question 8

what happens in the termination step?

Answer 8

two free radicals react to form a stable product
when two become one
*CH3 + *CH3—> C2H6

Question 9

which step continues multiple times?

Answer 9

the propagation step continues numerous times to result in multiple substitutions
—– IT IS A CHAIN REACTION

Question 10

why is the use of this mechanism limited in organic synthesis?

Answer 10

the nature of the reaction creates multiple products (it can terminate at different positions in the carbon chain)