question_answer 87)

  Classify the following compounds as primary, secondary and tertiary halides. (i) l-Bromobut-2-ene      (ii) 4-Bromopent-2-ene           (iii) 2-Bromo-2-methylpropane

Answer:

                  (i) Since the rate of reaction of compound 'A'  with aq. KOH depends upon the concentration of compound 'A' only, therefore, the reaction occurs by mechanism and the compound 'A' 2-bromo-2- methylpropane or tert-butyl bromide. (ii) Since compound 'B' is optically active and is an isomer of compound 'A' with MF C4HgBr, therefore, compound 'B' must be 2-bromobutane. Further, since the rate of reaction of compound 'B' with aq. KOH depends both' upon the concentration of compound 'B' and KOH, therefore, the reaction occurs by mechanism. Since in  reactions, nucleophile attacks from the back side, therefore, the product of hydrolysis (i.e. 2-butanol) will have inverted configuration w.r.t. to 2-bromobutane.