Chapter 24, Problem 4Q

Interpretation Introduction

Interpretation:

Structures corresponding to the peaks should be explained.

Concept introduction:

Mass spectrometry is an important spectroscopic method to determine the molecular weights and molecular formulas of the compounds. It also can help in the identification of compound or determination of its structure.

A mass spectrograph is plotted between the intensity of ions on the y-axis and $\text{m/z}$ on the x-axis.

Mass spectrometry is performed as follows:

• A sample is converted into a gaseous ion by an ionization technique in the mass spectrometer.
• Then on the basis of mass-to-charge $\text{m/z}$ ratios, gaseous ions are arranged.
• And these ions when generate electricity a mass spectrum is formed.

To assign the molecular weights to compounds the rule of thirteen is used in mass spectrometry. Thirteen here is obtained by adding the mass of carbon and hydrogen.

If the molecular ion peak is intense then $\text{M+1}$ and $\text{M+2}$ the peak will also be observed. And the ratio of intensities of $\text{M+1}$ and $\text{M+2}$ predict the presence of halogen isotopes.

If the ratio of $\text{M+1}$ and $\text{M+2}$ peak is 1:1 then bromine isotopes are present in the mixture and if 1:3 is the intensity ratio then the presence of chloride isotope is confirmed.

The peak intensity ratio depends on the abundance of isotopes in nature.