Q 47 E - Organic Chemistry (Mcmurry)

Question

Question: Nitriles,$\mathbf{R}\mathbf{-}\mathbf{C}\mathbf{\equiv }\mathbf{N}$ , undergo a hydrolysis reaction when heated with aqueous acid. What is the structure of the compound produced by hydrolysis of propanenitrile, ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{C}\mathbf{\equiv }\mathbf{N}$ , if it has IR absorptions from $\mathbf{2500}\mathbf{-}\mathbf{3100}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ and at $\mathbf{1710}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ , and has  ${\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{74}$?

Step-by-Step Solution

Answer

Step 1: IR spectroscopy

The N-H functional group of amine can be easily detected using the IR spectroscopy. It shows a characteristic absorption in the range 3300 to $\mathbf{3500}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ . An N-H absorption band is less intense in comparison to the O-H absorption band.

Step 2: Structure of the compound from the given data

The m/z value of the product is 74. The IR spectrum shows that the compound has IR absorptions at the values $2500-3100 {\mathrm{cm}}^{-1}$ and at $1710 {\mathrm{cm}}^{-1}$ .

When the nitrile undergoes hydrolysis forms carboxylic acid. The given propane nitrile,  ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{C}\equiv \mathrm{N}$ undergoes hydrolysis to give propionic acid.

IR absorptions at the values from $2500-3100 {\mathrm{cm}}^{-1}$ indicates the hydroxyl group at the carboxylic acid. The value at $1710 {\mathrm{cm}}^{-1}$ indicates the carbonyl group of the carboxylic acid functional group.

The molecular weight of the compound matches with the expected compound. The structure of the compound can be given as: