Module 4: Analysis
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Mass spectrometry What happens in the mass spectrometry
High energy electron bombards a molecules in a mass spectrometer which results in the molecule losing an electron
Mass spectrometry What is the resulting species when a molecule is bombarded by the higher energy electron
Molecular ion
Mass spectrometry Equation for formation of molecular ion
Molecule —-> Molecule+. + e-
Mass spectrometry Notation for molecular ion
M+
Mass spectrometry What is the definition of a molecular ion
Positive ion formed when molecule loses an electron
Mass spectrometry What is on the axis of a spectra
X- m/z -mass to charge ratio Y- %abundance
Mass spectrometry Where is the M+ ion on a spectra
Last peak on the right
Mass spectrometry What is fragmentation
Process in mass spec that causes positive ion (M+) to split into pieces of a positive ion (which produces a peak) and a radical
Mass spectrometry What is the M+1 peak
Smallll peak just after M+
Mass spectrometry Why is the M+1 peak there
Due to C-13 present
Mass spectrometry How is it used for isotopes
Positions of peaks show different isotopes prescence and is used to find relative atomic mass with abundance
Mass spectrometry How can organic molecules be identified from eac other
Each have different peaks from fragments
Mass spectrometry How does fragmentation occur and how does it show on spectra
One bond broken in the M+ to form a positive ion and radical Peak at the positive ion formed with its m/z value (mr)
Mass spectrometry Where is the Mr of the whole product found
At the M+ ion
Mass spectrometry For analysis questions what is the typical way to find the molecular formula
Find the empirical formula and find mr Find mr of whole product at the M+ peak mr of whole product / Mr of empirical Scale up the ration of the empirical formula
Mass spectrometry What are fragmentation patterns of functional groups
Specific positions of peaks and differences between major peaks which makes it possible to identify the type of compound
Mass spectrometry What is the peak due to at m/z 15
CH3+
Mass spectrometry What is the peak due to at m/z 29
C2H5+
Mass spectrometry What os the peak due to at m/z 43
C3H7+
Mass spectrometry For alkanes what affects the abundance of a peak
The stability of the carbo cation
Mass spectrometry For alkanes as the stability of the carbocation increases what happens to the peak
Larger abundance
Mass spectrometry For haloalkanes why is there often multiple peaks in the molecular ion region
Due to the different isotopes of the halogen
Mass spectrometry For ketones and aldehydes what is the characteristic fragmentation
Cleavage of bonds next to carbonyl (C=O)
Mass spectrometry Where do carbonyl compound fragments
Ether side of the carbonyl group