39E - Organic Chemistry (Mcmurry)

Question

Carvone is an unsaturated ketone responsible for the odour of spearmint. If carvone has  in its mass spectrum and contains three double bonds and one ring, what is its molecular formula?

Step-by-Step Solution

Answer

The molecular formula of carvone is ${\mathrm{C}}_{10}{\mathrm{H}}_{14}\mathrm{O}$.

Definition of Mass spectrum

The mass spectrum is a plot that shows the molecular weight of the unknown compound in terms of peaks. These peaks define the molecular weight of the compound.

Mass spectrum of carvone

From the mass spectrum, carvone has ${\text{M}}^{\text{+}}\text{=150}$. It contains one oxygen atom so 150-16=34. It can be divided by 12 to get the number of carbon and hydrogen atoms, i.e. $\frac{\text{134}}{\text{12}}\text{=11}\left(\text{remainder\hspace{0.17em}2}\right)$ .

Molecular formula

So, the molecular formula may be ${\mathrm{C}}_{11}{\mathrm{H}}_2\mathrm{O}$ replacing one carbon atom with 12 hydrogen atoms will give the molecular formula  ${\mathrm{C}}_{10}{\mathrm{H}}_{14}\mathrm{O}$. Thus, the molecular formula of carvone is  ${\mathrm{C}}_{10}{\mathrm{H}}_{14}\mathrm{O}$.