Organic Chem

Why liquid NH3 USED for prparation of alkene from alkane has deep blue colour electrons?

Reaction is given as-

CH=CH + NH3 --- CH2=CH2

Sodium or lithium in liquid ammonia with alcohol is used for reduction. This reduction is known as Birch reduction. Only liquid ammonia is not used for reduction. As we know solution of alkali metals (like sodium, lithium) in liquid ammonia is blue in colour due to the presence of the ammoniated electrons. These electrons participate in Birch reduction. The solvated electrons add to unsaturated system, consider acetylene and form radical anion I. Radical anion I abstract electron from ammonia to give a vinyl radical II. Further transfer of electrons to vinyl radical II lead to the formation of vinyl anion III. Vinyl anion III accept proton and produce an alkene, IV.