Q 46 E - Organic Chemistry (Mcmurry)

Question

Question: Ketones undergo a reduction when treated with sodium borohydride, ${\mathbf{NaBH}}_{\mathbf{4}}$ .What is the structure of the compound produced by reaction of 2-butanone with ${\mathbf{NaBH}}_{\mathbf{4}}$  if it has an IR absorption at $\mathbf{3400}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ and ${\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{74}$ in the mass spectrum?

Step-by-Step Solution

Answer

Step 1: Reaction of ketone with sodium borohydride

Sodium borohydrides are selective reducing agents. Aldehydes and ketones get converted to alcohols when sodium borohydride functions as the reagent. Aldehydes yield primary alcohols and ketones yield secondary alcohols.

Step 2: Structure of the compound produced by reaction of 2-butanone with NaBH 4

The m/z value of the product is 74. The IR spectrum shows that the compound has an IR absorption of  $3400 {\mathrm{cm}}^{-1}$.

The ketone undergoes reduction with ${\mathrm{NaBH}}_4$ forming an alcohol. The given compound 2-butanone undergoes reduction with  ${\mathrm{NaBH}}_4$ to form 2-butanol. 

The IR absorption value at $3400 {\mathrm{cm}}^{-1}$ indicates the hydroxyl group in 2-btanol.

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