Question

Write a test to detect the presence of double bond in a molecule.

Answer 1

The Presence of a double bond in a molecule can be detected by bromine water test and Baeyer’s test. The molecules with a double bond decolourise bromine water and aqueous \[\ce{KMnO4}\].

\[\begin{array}{cc}
\phantom{}\ce{> C = C < + \underset{Brown}{Br2} -> > C - C <}\phantom{}\\
\phantom{.........................}|\phantom{.....}|\phantom{}\\
\phantom{...........................}\ce{\underset{Colourless}{\phantom{.}Br\phantom{...}Br}}\phantom{..}
\end{array}\]

\[\begin{array}{cc}
\phantom{...}\ce{> C = C <  ->[aq. KMnO4][(Purple)] > C - C <}\phantom{}\\
\phantom{..........................}|\phantom{....}|\phantom{}\\
\phantom{..............................}\ce{\underset{Colourless}{\phantom{.}OH\phantom{.}OH}}\phantom{...}
\end{array}\]