50E - Organic Chemistry (Mcmurry)

Question

One way to determine the number of acidic hydrogens in a molecule is to treat the compound with NaOD in D₂O, isolate the product, and determine its molecular weight by mass spectrometry. For example, if cyclohexanone is treated with NaOD in D₂O, the product has MW =102. Explain how this method works.

Step-by-Step Solution

Answer

The molecular weight of the product is determined by addition of the molar mass of the elements.

Step 1: Reaction

The given compound Cyclohexanone reacts with NaOD in D₂O. The reaction is as follows,

                           Chemical reaction of ketone with NaOD and D₂O

Step 2: Determination of molecular mass

The molecular weight of the product formed is,

$\begin{array}{c}\mathbf{Six}\mathbf{Carbons}\mathbf{=}\mathbf{6}\mathbf{\times }\mathbf{12}\mathbf{=}\mathbf{72}\\ \mathbf{Four}\mathbf{Deutrium}\mathbf{=}\mathbf{4}\mathbf{\times }\mathbf{2}\mathbf{=}\mathbf{8}\\ \mathbf{SIx}\mathbf{hydrogens}\mathbf{=}\mathbf{6}\mathbf{\times }\mathbf{1}\mathbf{=}\mathbf{6}\\ \mathbf{One}\mathbf{oxygen}\mathbf{=}\mathbf{1}\mathbf{\times }\mathbf{16}\mathbf{=}\mathbf{16}\\ \mathrm{Total}=102\end{array}$