spectroscopy Flashcards
what is infrared spectroscopy used for?
IR spectroscopy is usually used to identify the funtional groups in organic compounds
how does IR spectroscopy work?
different bonds absorb IR with slightly different wavenumbers
by examining the wavenumbers of the radiation that have been absorbed by a compound we can work out which bonds must have been present
concentrate on the stron peaks where transmission falls bellow 70%
what is the fingerprint region?
the section between 400 cm^-1 and 1500cm^-1
it is different for every compound and as a result if the fingerprint region is found to be the same as the fingerprint region of a known compound the unknown sample can be identified.
Nuclear magnetic resonance spectroscopy
NMR is a powerful technique which gives info about the position of H1 or C13 atoms in a molecule
it is the same technology that is used in magnetic resonance imaging (MRI)
MRI scans are a non invasive way of diagnosing patients. they allow medical staff to gain knowlege of whats happening iside a patients body without the possible complications associated with operating on the patient.
MRI scans are very useful but due to the stron magnetic fields used they are unsuitable for patients with heart pacemakers
the chemical shift
if atoms have an odd mass number then their nuclei will have spin, this spin can be detected using radio frequencies
depending on their molecular environment around the H1 or C13, their precise resonance frequency will vary slightly
this slight variation can give info about the structure of the compound
to allow chemists to compare the spectra produced on different machines, a reference compound is added to the sample
the differences between the resonance frequencies of the H1 or C13 atoms in the sample and in the reference are measured. these are know as the shifts
chemical shift is measured in parts per million (ppm)
why is TMS used as the reference standard for NMR?
it is fairly cheap
it does not react with the sample being analysed
all the carbon atoms are equivalent so it only produces one strong peak, which is usually upfield from the peaks produced by the other H1 or C13 nuclei
