1. Lecture 22 Introduction to Mass Spectrometry Lecture Problem 7 Due
This week in lab:
Work on 1st Synthetic
Next week in lab:
Synthetic Experiment #2 PreLab Due
Ch 9 Final Report Due

2. Spectral Analysis 1H NMR: Bond connectivities
Types and kinds of protons
IR:
Functional groups
Now, let’s look at Mass Spectrometry:
Determine the mass of the sample
Look at fragmentation patterns determine “pieces”
of the molecule.

3. Mass Spectrum of Cyclohexamine
Fragments

4. Mass Spectrometry
How to get the mass of the sample or pieces of the sample:
Ionize the sample with a high energy particle to give
a molecular ion, M+ (a.k.a. parent ion).
Note: Ions may fragment which results in pieces of the sample.
When fragmentation occurs, there is always a positive
fragment (ion) and a neutral fragment.
Only positive species are detected by the detector. Thus,
only the mass of the molecular ion and the masses of
positive ion fragments will be read by the detector and appear
on the mass spectrum for the compound. Neutral fragments
are not read by the detector and do not appear on the spectrum.

5. Mass Spectrometry Basic Idea:
To ionize: bash the molecule with a high energy particle in a vacuum:
An electron (known as Electron Ionization) or
A proton (known as Chemical Ionization)
A molecular ion results:
Electron Ionization (EI): M + e-  M+•
Chemical Ionization (CI): M + H+  MH+
Send molecular ion through a magnetic field
Molecular ion travels and reaches a detector. The detector
only detects positively charged species  m/z ratio (mass/
charge).
Obtain mass of molecular ion and fragments. The intensity of the signals
is proportional to the number of ions. The more intense the signal, the
more stable that ion is.

6. A quadrupole mass spectrometer.
The Mass Spectrometer
A quadrupole mass spectrometer.
Ions oscillate as they move through the electric fields on the four rods.
Resonant ions hit the detector.
Nonresonant ions are deflected and don’t hit the detector.

7. Molecular Ions Molecular ions of different compounds have different
stabilities and, therefore, different fates.
Some will reach the detector.
Others will fragment before they reach the detector.
Molecular ions of different compounds will have different
intensities:
Strong in aromatics
Weak in alkanes, alcohols & others

8. Mass Spectrum of Hexane

9. Molecular Ions M+ = 78 Benzene Strong M+ M+ = 86 Hexane Weak M+
Hexanol
M+ not seen

10. Nitrogen Containing Compounds
If odd # of N’s, then odd mass. If even mass, then either zero N’s or even # of N’s.
M+ = 99
Cyclohexamine

11. Molecular Ions
Molecular Ions = sum of atomic weight(s) of all isotopes of all elements in a molecule. If you had 10,000 atoms of each type:
C: C atoms C atoms
H: H atoms 1 2H atoms
O: O atoms, O atoms, O atoms
N: N atoms N atoms
Cl: Cl atoms Cl atoms (3:1 35Cl:37Cl)
Br: Br atoms Br atoms (1:1 79Br:81Br)

12. Mass Spectrum of Hexane87
Hexane with one 13C atom: M + 1