question_answer 29)

The treatment of alkyl chlorides with aqueous KOH leadsto the formation of alcohols but in the presence of alcoholic KOH, alkenesare major products. Explain. Difference lies in the mode and extent of dissociation of KOH in thepresence of different solvents. is a good nucleophile while  is a strong base.  

Answer:

In the presence of water, KOH dissociates completely into ions. These are strong nucleophiles and produce alcohols from alkyl halides. Hydration of ions also takes place. So they are not able toabstract  from -atom. So alkenes are not formed. In alcoholicmedium, solution also contains , ethoxide ions in addition to ions. Being a stronger base, they abstract  ion from. -C-atom givingrise to alkene. (Dehydrohalogenation).