IR radiation is absorbed by the covalent bonds. This makes them stretch or bend.
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Stretch
It is the increasing or decreasing distance between the centres of atoms caused by the absorbance of energy.
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Bend
Vibration causes a change in bond angle.
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Why is this method used?
Bonds between different atoms and bonds in different places absorb different frequencies.
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Do heavier or lighter bonds vibrate quicker?
Heavier atoms vibrate more slowly than lighter atoms.
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Do slower or faster bonds vibrate quicker?
Stronger bonds vibrate faster than slower bonds.
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Why is wavenumber used instead of frequency.
Wavenumber is proportional to frequency. It is used instead as frequencies are very large.
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Why do we use IR spectroscopy?
Helps to identify functional groups meaning organic molecules can be identified.
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Negatives of infrared radiation.
Causes global warming. Water vapour, carbon dioxide and methane absorb the long wavelengths of IR and re-emits them as radiation which increases the temperature of the atmosphere.
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What is the fingerprint region?
The peaks below 1500 cm which contains unique peaks which can be used to identify a particular molecule.
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Uses of infrared spectroscopy
Identifying pollutants by fingerprint region. Breathalysers.
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What happens in a mass spectrometer?
An organic compound is placed in the spectrometer and it loses an electron forming a positive ion.
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Mass to charge ratio
The spectrometer detects the mass to charge ratio which gives the molecular mass of the compound.
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Small peak next to the molecular ion peak
Represents the 1.1% of carbon which exists as the isotope carbon-13.
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What is fragmentation?
In the mass spectrometer some molecular ions break down into smaller pieces called fragments.
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How fragmentation works
Ion --> ion + free radical
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Why are fragments important?
All compounds fragment in different ways. Meaning these can be identified to help recognise a compound.
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To work out the number of carbon atoms
(M+1 peak / M peak) x 100
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Uses of mass spectrometry
Drug testing, looking for toxins.
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What is the molecular ion peak? M+
The molecule which is being analysed with one electron removed from it.
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Other cards in this set
Card 2
Front
Stretch
Back
It is the increasing or decreasing distance between the centres of atoms caused by the absorbance of energy.
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