Question

How can I explain the monochlorination of alkanes?

Answer 1

Alkanes are saturated hydrocarbons in which all the valency of a carbon atom is satisfied with the other atom therefore alkanes mainly gives substitution reaction. Alkenes and alkynes are unsaturated hydrocarbons in which one or two valencies of carbon atom are not satisfied with other atoms therefore it can give additional reactions.

Complete step by step answer:
Organic chemistry is the branch of chemistry in which carbon and its compounds are studied on a large scale. In organic chemistry, mainly carbon and hydrogen related compounds are present which are known as hydrocarbon.
Hydrocarbons are the compounds in which carbon and hydrogen are present and it is mainly classified in saturated and unsaturated hydrocarbons. In saturated hydrocarbons all the valencies of carbon atoms are satisfied with carbon or other atoms and they are also known as alkane.
In unsaturated hydrocarbons, one or two valencies of carbon atom are not satisfied with carbon or other atoms therefore carbon forms double or triple bonds with another carbon atom and they are also known as alkene and alkyne respectively.
Alkanes are saturated hydrocarbons in which all four valencies of carbon atom are satisfied therefore it does not give additional reactions. Alkanes mainly give substitution reactions in which one of the hydrogen atoms of alkane is replaced with another atom.
In mono halogenation of alkane, one of the H-atoms of alkane is replaced by halogen atom X $(X=F,Cl,Br,l)$ and it forms mono halogenated alkane as a product. The mono halogenations reaction takes place through free radical mechanism, in which formation of free radical takes place in presence of sunlight or in presence of peroxide.
The rate of halogenation of halogen is as follows $F>Cl>\operatorname{Br}>\operatorname{l}$
The rate of halogenation of alkane is as follows ${{1}^{{}^\circ }}alkane<{{2}^{{}^\circ }}alkane<{{3}^{{}^\circ }}alkane$
Final answer:
The mono halogenation of alkane takes place through free radical mechanism and it contains three steps:-
1. Initiation step- formation of halogen free radical in presence of sunlight or peroxide.
2. Propagation step- formation of carbon free radical through halogen free radical.
3. Termination step- The step in which all the free radicals terminate.

Note:
Mono fluorination of alkane is an explosive step so it must take place with precaution while mono iodination of alkane is a very slow step which mainly takes place in presence of some oxidizing agent.