Infrared spectoscopy
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Transcript of Infrared spectoscopy
![Page 1: Infrared spectoscopy](https://reader035.fdocuments.net/reader035/viewer/2022062820/58ac117a1a28ab33178b5a97/html5/thumbnails/1.jpg)
Infrared spectoscopyMonday 1 May 2023
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Irradiation with IR causes molecules to absorb the radiation as the bonds stretch or bend.
The energy needed to stretch or bend a bond depends on – the bond strength
- the bond length - the mass of the atoms in the
bond The frequencies absorbed are called ‘peaks’
although they are really troughs on the graphic printout.
Origin of IR spectra
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The parts of a IR spectrometer.
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An infrared spectrometer
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Only molecules that change their polarity when they vibrate absorb IR.
So molecules such as H2 or Cl2 do not absorb IR but HCl does.
Which molecules absorb IR.
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Stronger bonds require more energy to make them stretch of bend so their peaks occur at higher wavenumber (cm-1) values.
Hydrogen bonding results in a major widening of the O-H peak.
Position of the peaks
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Molecules having more than two atoms can vibrate in different ways – this results in a variety of peaks being produced.
More complex shapes
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Main regions of absorbtions
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Main regions of absorbtions
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IR spectrum of ethanol
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IR spectrum of propanoic acid
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IR spectrum of ethanal
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IR spectrum of ethanoic acid
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