CHEM1112 Lecture Notes - Lecture 6: Mass Spectrum, Molecular Mass, Electric Field
19 May 2018
School
Department
Course
Professor
Identify the molecular ion, base peak and daughter
ions in a mass spectrum
Molecular masses and molecular formulae different
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To determine molecular formula, need molecular mass
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Mass spec -> molecular mass
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Screen clipping taken: 21/08/2017 9:56 PM
Daughter ions - smaller ions formed from when some ions
fragment (fragmentation), which can help determine
STRUCTURE of the molecule
▪
Molecules ionised by impact with electrons in a vacuum, ie.
Turned into charged species (ions)
1.
Ions accelerated through an electric field
2.
Beams of ions directed into magnetic field, causing ions to
bend
▪
Ions trace out circular paths, whose radii dependant on m
and z (but charge z is almost always 1)
▪
Detector measures how far ions have bent -> can calculate
m
▪
Ions separated according to mass/charge or m/z
3.
Results from loss of one electron from the parent molecule
▪
Electron is so light that mass of the molecular ion is the
same as the parent molecule
▪
Molecular ion - heaviest possible ion
4.
Measures mass of molecules
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Typical mass spectrum has 1 molecular ion and many daughter ions
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Screen clipping taken: 21/08/2017 10:34 PM
6.1
Monday, 21 August 2017
9:46 PM
6. Structural determination Page 1
Screen clipping taken: 21/08/2017 10:34 PM
Base peak - most intense signal, intensity is set to 100%
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6. Structural determination Page 2
Recognise that a fragmentation pattern in a mass spectrum can lead
to structural information
Fragmentation -> daughter ions -> help determine structure of molecule
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6.2
Monday, 21 August 2017
9:47 PM
6. Structural determination Page 3
Document Summary
Identify the molecular ion, base peak and daughter ions in a mass spectrum. Molecules ionised by impact with electrons in a vacuum, ie. turned into charged species (ions) Daughter ions - smaller ions formed from when some ions fragment (fragmentation), which can help determine. Beams of ions directed into magnetic field, causing ions to bend. Ions trace out circular paths, whose radii dependant on m and z (but charge z is almost always 1) Detector measures how far ions have bent -> can calculate m. Results from loss of one electron from the parent molecule. Electron is so light that mass of the molecular ion is the same as the parent molecule. Typical mass spectrum has 1 molecular ion and many daughter ions. Screen clipping taken: 21/08/2017 10:34 pm: structural determination page 1. Base peak - most intense signal, intensity is set to 100: structural determination page 2.
