Question:

Which of the following will not form a yellow precipitate on heating with an alkaline solution of iodine?

Updated On: Jul 12, 2022
  • $CH_3CH(OH)CH_3$
  • $CH_3 CH_2 CH(OH)CH_3$
  • $CH_3 OH$
  • $CH_3 CH_2 OH$
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The Correct Option is C

Solution and Explanation

An organic compound form yellow precipitate of iodoform with ${{I}_{2}}$ in presence of alkali, if it has$\text{C}{{\text{H}}_{\text{3}}}\text{CO}$ group directly or it has $C{{H}_{3}}-\underset{\begin{smallmatrix} | \\ OH \end{smallmatrix}}{\overset{\begin{smallmatrix} H \\ | \end{smallmatrix}}{\mathop{C}}}\,$ group $\text{C}{{\text{H}}_{\text{3}}}\text{CH}\left( \text{OH} \right)\text{C}{{\text{H}}_{\text{3}}}+{{\text{l}}_{\text{2}}}\text{ }\xrightarrow{\text{NaoH}}\text{ C}{{\text{H}}_{\text{3}}}\text{COC}{{\text{H}}_{\text{3}}}$ $\begin{align} & \,\,\,\,\,\,\,\,\,\,+\text{ }2HI+3NaI+C{{H}_{3}}COONa+\underset{{}}{\mathop{3{{H}_{2}}O}}\, \\ & C{{H}_{3}}COC{{H}_{3}}+3{{I}_{2}}+4NaOH\xrightarrow{{}}\underset{\begin{smallmatrix} \text{yellow} \\ \text{ppt}\text{.} \end{smallmatrix}}{\mathop{CH{{I}_{3}}}}\,\downarrow \\ \end{align}$ $+\text{ }3NaI+C{{H}_{3}}COONa+3{{H}_{2}}O$ $C{{H}_{3}}C{{H}_{2}}CH\left( OH \right)\text{ }C{{H}_{3}}+{{I}_{2}}\xrightarrow[{}]{{}}$ $\underset{Ethyl\,methyl\,ketone}{\mathop{C{{H}_{3}}C{{H}_{2}}\underset{\underset{O}{\mathop{||}}\,}{\mathop{C}}\,C{{H}_{3}}+2HI}}\,$ It gives iodoform test. $\text{C}{{\text{H}}_{\text{3}}}\text{C}{{\text{H}}_{\text{2}}}\underset{\underset{\text{O}}{\mathop{||}}\,}{\mathop{\text{C}}}\,\text{C}{{\text{H}}_{\text{3}}}+\text{3}{{\text{l}}_{\text{2}}}+\text{4NaOH }\to $ $\underset{\text{Yellow}\,\text{ppt}\text{.}}{\mathop{\text{CH}{{\text{I}}_{\text{3}}}}}\,\downarrow +\text{3NaI+C}{{\text{H}}_{\text{3}}}\text{C}{{\text{H}}_{\text{2}}}\text{COONa+3}{{\text{H}}_{\text{2}}}\text{O}$ $\text{C}{{\text{H}}_{\text{3}}}\text{OH}+{{\text{1}}_{\text{2}}}\text{ }\xrightarrow{{}}\text{ HCHO}+\text{2HI}$ It does not have methyl ketonic group, so it does not give yellow ppt. with ${{\text{I}}_{\text{2}}}$ in presence of alkali. $\text{C}{{\text{H}}_{\text{3}}}\text{C}{{\text{H}}_{\text{2}}}\text{OH}+{{\text{1}}_{\text{2}}}\xrightarrow{\text{ }}\text{ C}{{\text{H}}_{\text{3}}}\underset{\underset{\text{O}}{\mathop{||}}\,}{\mathop{\text{C}}}\,\text{H}+\text{2HI}$ It gives iodoform test. $\text{C}{{\text{H}}_{\text{3}}}\underset{\underset{\text{O}}{\mathop{||}}\,}{\mathop{\text{C}}}\,\text{H}+\text{3}{{\text{I}}_{\text{2}}}+\text{4NaOH }\xrightarrow{{}}\underset{\text{Yellow}\,\text{ppt}\text{.}}{\mathop{\text{CH}{{\text{l}}_{\text{3}}}}}\,$ $+HCOONa+3NaI+2{{H}_{2}}O$
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Concepts Used:

Alcohols, Phenols, and Ethers

Alcohol is formed when a saturated carbon atom bonds to a hydroxyl (-OH) group. It is an organic compound that contains a hydroxyl functional group attached to a carbon atom.

Phenol is formed when the -OH group replaces the hydrogen atom in benzene. It is an organic compound in which a hydroxyl group directly attaches to an aromatic hydrocarbon.

Ether is formed when oxygen atom bonds to two alkyl or aryl groups. It is an organic compound that has an oxygen atom that is connected to two aryl and alkyl groups.

Read More: Alcohol, Phenol, and Ethers