Question

Consider the following substances

$1.$ $C{H}_{3}C\equiv CC{H}_3$

$2.$ $C{H}_{3}C{H}_{2}C\equiv CH$

$3.$ $C{H}_{3}CH=CHC{H}_3$

$4.$ $C{H}_{3}C{H}_{2}CH=C{H}_2$

Which of the following reagent can be used to distinguish the compound (2) from the rest of the compounds?

• A. Bromine/ $CC{l}_4$
• B. Bromine/ $C{H}_{3}COOH$
• C. Alk. $KMn{O}_4$
• D. Ammonical $AgN{O}_3$ or ammoniacal cuprous chloride

Answer 1

Answer: (D)

Compound (2) has acidic hydrogen (acetylinic hydrogen), which can be replaced.

$C{H}_3-C{H}_2-C\equiv CH+{\left(\left[Ag{\left(N{H}_3\right)}_2\right]\right)}^{+}O{H}^{-}\to \underset{\left(\text{White ppt}\right)}{C{H}_3-C{H}_{2}C\equiv CAg}+H_{2}O+2N{H}_3$

$C{H}_{3}C{H}_{2}C\equiv CH+{\left(\left[Cu{\left(N{H}_3\right)}_2\right]\right)}^{+}O{H}^{-}\to \underset{\left(\text{Red ppt.}\right)}{C{H}_{3}C{H}_{2}C\equiv CCu}+H_{2}O+2N{H}_3$

Compounds 1, 3 and 4 have no acidic hydrogen. Therefore, they do not react with reagent option D.