The alkyl halide `C_4 H_9 Br `(A) reacts with alcoholic KOH and gives an alkene (B) which reacts with bromine to give a dibromide (C). (C) is transformed with sodamide into a gas (D) which forms a precipitate when passed through ammoniacal silver nitrate solution. Give the structural formulae of the compounds (A), (B), (C) and (D) and explain the reactions involved.

Explanation

The compound A is `underset(underset((C_(4)H_(9)Br))("1-bromobutane"))(CH_(3)CH_(2)CH_(2)CH_(2)Br)`
The compound B is `underset("1-Butene")(CH_(3)- CH_(2) underset(())- CH= CH_(2))`
The compound C is `underset(underset( (C ))("1, 2-dibromobutane"))(CH_(3)-CH_(2)-overset(overset(Br)(|))(CH)-CH_(2)Br)`
The compound D is `underset(underset((D)) ("But-1-yne"))(CH_(3)-CH_(2)-C -= CH)`
As compound D forms precipitate with ammoniacal silver nitrate, it must be a terminal alkyne and must contain C-triple bond CH group. D is obtained from C by the action of sodamide (a dehydrohalogenating agent). C must be a 1, 2-dibromo derivative. Compound C is obtained by the action of bromine, on the alkene B. Therefore, B should be a 1-alkene and consequently A should be 1-bromobutane. The suitable reactions are given below:
`underset(underset(underset((A))((C_(4)H_(9)Br)))("1-bromobutane"))(CH_(3)CH_(2)CH_(2)CH_(2)Br) + KOH (alc) rarr underset(underset((B))("But-1-ene"))(CH_(3)-CH_(2)-CH)= CH_(2) + KBr + H_(2)O " " CH_(3)- underset((B))(CH_(2)-CH)= CH_(2) + Br_(2) rarr underset(underset((C ))("1, 2-dibromobutane"))(CH_(3)-CH_(2)- overset(overset(Br)(|))(CH)-CH_(2)Br)`
`CH_(3) - underset(underset(H)(|))overset(overset(H)(|))(C )- underset(underset(H)(|))overset(overset(Br)(|))(C )- underset(underset(Br)(|))overset(overset(H)(|))(C )- H underset(-2HBr)overset(NaNH_(2))rarr underset(underset((D))("But-1-yne"))(CH_(3)-CH_(2)-C-= CH)`
`CH_(3)- CH_(2)-C -= CH + [Ag(NH_(3))_(2)] NO_(3) rarr underset(underset(("White precipitate"))("Silver butynide"))(CH_(3)-CH_(2)-C)-= overset(-)(C ) overset(+)(A)g + NH_(4)NO_(3) + NH_(3)`