Chapter 14, Problem 62P

Interpretation Introduction

Interpretation:

The structure should be drawn given the molecular ion $m/z$ value of carboxylic acid.

Concept introduction:

Fundamental of Mass spectrometer: It is one of powerful tool in organic chemistry, used to quantity known materials, to identify unknown compounds within a sample and to elucidate the structure and chemical properties of different molecules.

Basic principle: It generates multiple ions from the sample under investigation, it than separates them according to their specific mass to charge ration (m/z) and records the relative abundance (RA) of each ion types.

$\begin{array}{l}\text{M}\stackrel{\begin{array}{l}electron\\ beam\end{array}}{\to }{\text{M}}^{\begin{array}{l}+\\ .\end{array}}+e^{-}\\ \text{[Molecule]}\text{molecular ion}electron\\ [\text{Radical}\text{cation}]\end{array}$

The molecular ion and fragment ions produced in a mass spectrometer and recorded by it are unique for each compound. A mass spectrum, therefore, like a fingerprint of the compound.

Interpreting a mass spectrum:

1. 1. The each m/z values is the m/z value of one the fragments to the nearest whole number.
2. 2. The peak with the highest m/z value in the molecular ions (M⁺), the fragment that results when the molecules lose an electrons as result of being bombarding by the electron beam.
3. 3. The m/z value of the molecular ion gives the molecular mass of the compound.
4. 4. Peaks with smaller m/z values, fragment ion peak represent positively charged fragments of the molecular ion.