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Question
Give a simple chemical test to distinguish between the following pair of compounds:
Pentan-2-one and Pentan-3-one
Solution
Pentan-2-one and pentan-3-one can be distinguished by the iodoform test.
Iodoform test: Pentan-2-one is a methyl ketone, so it responds to the iodoform test. However, pentan-3-one is not a methyl ketone and does not respond to this test.
\[\begin{array}{cc}
\ce{O}\phantom{.................................................}\\
||\phantom{.................................................}\\
\ce{\underset{Pentan-2-one}{CH3CH2CH2 - C - CH3} + 3NaOI ->\underset{Sodium butanoate}{CH3CH2CH2COONa} + \underset{(yellow ppt)}{\underset{Iodoform}{CHI3\downarrow}} + 2NaOH}\
\end{array}\]
\[\begin{array}{cc}
\ce{O}\phantom{.......................................}\\
||\phantom{.......................................}\\
\ce{\underset{Pentan-3-one}{CH3CH2 - C - CH2CH3} + NaOI -> No yellow ppt of iodoform}\
\end{array}\]
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