Chapter 24, Problem 5Q

Interpretation Introduction

Interpretation:

The fragmentation that leads to a peak at $\text{m/z}$ of 127,125 and 105 should be determined.

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 y-axis and $\text{m/z}$ on x axis. Mass spectrometry works 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 $\left(\text{m/z}\right)$ ratios, gaseous ions are arranged.
• These ions generate electric current at detector and a mass spectrum is formed.

To assign the molecular weights to compounds the rule of thirteen is utilized in mass spectrometry. Thirteen here is obtained by the addition of 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. The ratio of intensities of $\text{M+1}$ and $\text{M+2}$ predict the existence 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.