Question

Draw the structures of major monohalo products in each of the following reactions: 


(b) Give reasons for the following:
(i) Grignard reagent should be prepared under anhydrous conditions.
(ii) Alkyl halides give alcohol with aqueous KOH whereas in the presence of alcoholic KOH, alkenes are formed

Hint:

Grignard reagents require dry conditions to avoid unwanted reactions with moisture. Aqueous KOH favors substitution, and alcoholic KOH promotes elimination to form alkenes.

Answer 1

(a) (i) The major product of the reaction between ethene and HBr is 1-bromoethane (CH₃CH₂Br). 

(ii) The product of the reaction between benzene and Br₂ in UV light is bromobenzene (C₆H₅Br).

(b) (i) Grignard reagents are highly reactive and react with water to form hydrocarbons, so they should be prepared under anhydrous conditions to prevent hydrolysis.

(ii) Aqueous KOH leads to nucleophilic substitution, forming alcohols, while alcoholic KOH leads to elimination reactions, producing alkenes.