Ryan Mulcahy
Interpretation of Spectra
Infrared Spectroscopy
Infrared spectroscopy is the most frequently used scientific technique by scientists.
This is due to spectroscopy being able to identify a great variety of different
compounds and structures. Scientists can identify different functional groups as the
spectroscopy allows them to see multiple compounds and different chemical
properties. Functional groups intake different frequencies of energy in two different
ways, this is known as bending or stretching; this types of frequencies are in
functional groups to allow the knowledge of a molecule. Infrared spectrometry is
used to examine how pure a certain sample is, the spectra of a pure sample, spectra
of other samples of the same compound can be compared to the original sample;
impurities cause extra peaks across the spectra, they can be compared to existing
logs. If there is more than one peak, this can indicate that there is more than one
compound that is in the sample. The absorbance is different for each separate bond.
C=O is different to C-O.
C Nuclear Magnetic Resonance
C Nuclear Magnetic Resonance is dependent on the magnetic properties of C 13 as
this has magnetic properties; this provides direct information about the carbon
skeleton of a molecule as it can be used to determine the number of carbon atoms in
a molecules and the different types of carbons atoms present. If the carbon atoms in
a molecule are bonded to different functional groups or have different bonds, they
have different environments and therefore are seen as different peaks in C NMR
spectrum. If 2 or more carbon atoms have the exact same environment as they may
be bonded to the same carbon, then they will only be seen as one large peak.
Despite only 1% of all carbon atoms being C , the C NMR that relies on the
13
presence of C still works as a solution and unknown mixture will contain large
13
numbers of the same molecule and therefore there is a chance that that each of the
carbon environments contains a C in at least 1 molecule. In order for the carbon to
13
be detected it can be in any molecule, it is not necessary for both of the C to be in
13
the same molecule. In a carbon NMR multiple individual scans are accumulated to
form a spectrum. The atoms that neighbour a carbon atom all have different
electronegative properties and different functional groups also behave differently in
electron donating and withdrawing. These different characteristics allow different
carbon environments to be identified as previously known compounds are scanned
and the chemical shift patterns of the bonds and functional groups are logged which
allows for comparison. Unlike H NMR there is no splitting or coupling in peaks in a C
NMR as it is very unlikely for there to be more than 1 C atom present in a molecule.
13
Mass Spectrometer
Mass spectrometer measures the molecular mass of any unknown substance. On a
mass spectrum the peak with the highest m/z value (to the furthest right) is the
relative molecular mass of the unknown substance. Inside a mass spectrometer the
sample is ionised using an electron gun which causes it to lose an electron. These
ions are accelerated using a magnetic field and then detected. The sample needs to
be ionised in order for the atoms to be accelerated and then detected. The different
atoms with different masses separate during acceleration, as ions with a low mass
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Interpretation of Spectra
Infrared Spectroscopy
Infrared spectroscopy is the most frequently used scientific technique by scientists.
This is due to spectroscopy being able to identify a great variety of different
compounds and structures. Scientists can identify different functional groups as the
spectroscopy allows them to see multiple compounds and different chemical
properties. Functional groups intake different frequencies of energy in two different
ways, this is known as bending or stretching; this types of frequencies are in
functional groups to allow the knowledge of a molecule. Infrared spectrometry is
used to examine how pure a certain sample is, the spectra of a pure sample, spectra
of other samples of the same compound can be compared to the original sample;
impurities cause extra peaks across the spectra, they can be compared to existing
logs. If there is more than one peak, this can indicate that there is more than one
compound that is in the sample. The absorbance is different for each separate bond.
C=O is different to C-O.
C Nuclear Magnetic Resonance
C Nuclear Magnetic Resonance is dependent on the magnetic properties of C 13 as
this has magnetic properties; this provides direct information about the carbon
skeleton of a molecule as it can be used to determine the number of carbon atoms in
a molecules and the different types of carbons atoms present. If the carbon atoms in
a molecule are bonded to different functional groups or have different bonds, they
have different environments and therefore are seen as different peaks in C NMR
spectrum. If 2 or more carbon atoms have the exact same environment as they may
be bonded to the same carbon, then they will only be seen as one large peak.
Despite only 1% of all carbon atoms being C , the C NMR that relies on the
13
presence of C still works as a solution and unknown mixture will contain large
13
numbers of the same molecule and therefore there is a chance that that each of the
carbon environments contains a C in at least 1 molecule. In order for the carbon to
13
be detected it can be in any molecule, it is not necessary for both of the C to be in
13
the same molecule. In a carbon NMR multiple individual scans are accumulated to
form a spectrum. The atoms that neighbour a carbon atom all have different
electronegative properties and different functional groups also behave differently in
electron donating and withdrawing. These different characteristics allow different
carbon environments to be identified as previously known compounds are scanned
and the chemical shift patterns of the bonds and functional groups are logged which
allows for comparison. Unlike H NMR there is no splitting or coupling in peaks in a C
NMR as it is very unlikely for there to be more than 1 C atom present in a molecule.
13
Mass Spectrometer
Mass spectrometer measures the molecular mass of any unknown substance. On a
mass spectrum the peak with the highest m/z value (to the furthest right) is the
relative molecular mass of the unknown substance. Inside a mass spectrometer the
sample is ionised using an electron gun which causes it to lose an electron. These
ions are accelerated using a magnetic field and then detected. The sample needs to
be ionised in order for the atoms to be accelerated and then detected. The different
atoms with different masses separate during acceleration, as ions with a low mass
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