Write short notes on reactions and stability of free radials.

Question

(a) Write short notes on reactions and stability of free radials.
(b) Write the method for preparation and stability of carbocation.

Answer 1

(a) Free Radicals : Free radicals are chemical species that contain a singly occupied orbital. They are neutral and tend to be highly reactive. These have high tendency to pair with the unpaired electron. They readily combine with each other or with other molecules to pair their electrons. Some reactions of free radicals are given below
(i) Recombination into hydrocarbons

CH₃ + CH₃ → CH₃ - CH₃ 

(ii) Disproportination

CH₃CH₂ + CH₃CH₂ → CH₂ = CH₂ + CH₃CH₃ 

(iii) Reaction with olefins

The alkyl free radicals are unstable and highly reactive. These are of three types—Primary, Secondary and Tertiary alkyl free radicals. The relative order of stability amongst these free radicals is given as below 

Greater the +I effect, greater will be the stability of free radical.

(b) Carbocation : Carbocation are generally formed by means of heterolytic fission. These can be prepared by following methods :
(i) By direct ionization

(ii) By the protonation of unsaturated compounds

Carbocations are highly unstable and reactive species. Alkyl groups directly attached to the positively charged which stabilise the carbocations due to inductive and hyperconjugative effects. The relative order of stability of carbocations is given below