Chapter 17
17.1 MASS SPECTROMETRY
Molecular ion The positive ion formed in mass spectrometry
when a molecule loses an electron
How do you find the molecular mass from a Located the molecular ion peak (M+). This is the
mass spectrum? clear peak at the highest m/z value on the right-
hand side of the mass spectrum.
What is the M + 1 peak? It is a very small peak one unit after the M+ peak
and exists because 1.1% of carbon is present as
the carbon-13 isotope.
Fragmentation The process in mass spectrometry that causes a
positive ion to split into smaller pieces, one of
which is a positive fragment ion.
Fragment ions Ions formed from the breakdown of the molecular
ion in a mass spectrometer
Give the fragment ions for a peak at m/z=
15 CH3+
29 CH3CH2+
31 CH2OH+
45 CH3CH2O+
43 C3H7+
57 C4H9+
17.2 INFRARED SPECTROSCOPY
Mass spectrum Use of the molecular ion peak from a mass
spectrum to determine the molecular mass. Use
of fragment ions to identify sections of a molecule
Infrared spectroscopy Use of absorption peaks from a spectrum to
identify bonds and functional groups present in
the molecule.
Explain the principles infrared spectroscopy is Atoms in molecules have covalent bonds which
based on possess energy and vibrate naturally about a
central point. The bonds can absorb IR radiation
which makes them bend or stretch more. A
vibration called a bend results in a change in
bond angle. Any particular bond can only absorb
radiation that has the same frequency as the
natural frequency of the bond.
The amount that a bond stretches or bends The mass of the atoms in the bond- heavier atoms
depends on: vibrate more slowly than lighter atoms
The strength of the bond- stronger bonds vibrate
17.1 MASS SPECTROMETRY
Molecular ion The positive ion formed in mass spectrometry
when a molecule loses an electron
How do you find the molecular mass from a Located the molecular ion peak (M+). This is the
mass spectrum? clear peak at the highest m/z value on the right-
hand side of the mass spectrum.
What is the M + 1 peak? It is a very small peak one unit after the M+ peak
and exists because 1.1% of carbon is present as
the carbon-13 isotope.
Fragmentation The process in mass spectrometry that causes a
positive ion to split into smaller pieces, one of
which is a positive fragment ion.
Fragment ions Ions formed from the breakdown of the molecular
ion in a mass spectrometer
Give the fragment ions for a peak at m/z=
15 CH3+
29 CH3CH2+
31 CH2OH+
45 CH3CH2O+
43 C3H7+
57 C4H9+
17.2 INFRARED SPECTROSCOPY
Mass spectrum Use of the molecular ion peak from a mass
spectrum to determine the molecular mass. Use
of fragment ions to identify sections of a molecule
Infrared spectroscopy Use of absorption peaks from a spectrum to
identify bonds and functional groups present in
the molecule.
Explain the principles infrared spectroscopy is Atoms in molecules have covalent bonds which
based on possess energy and vibrate naturally about a
central point. The bonds can absorb IR radiation
which makes them bend or stretch more. A
vibration called a bend results in a change in
bond angle. Any particular bond can only absorb
radiation that has the same frequency as the
natural frequency of the bond.
The amount that a bond stretches or bends The mass of the atoms in the bond- heavier atoms
depends on: vibrate more slowly than lighter atoms
The strength of the bond- stronger bonds vibrate
