Infra-red spectroscopy and mass specrometry

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Infra-red Spectroscopy

Bonds vibrate in 2 different ways:

stretching

bending

Mass Spectrometry

We use wave numbers because frequencies in Hz are often VERY LARGE. If the TRANSMITTANCE is 100%, then no radiation is absorbed. You can identify the FUNCTIONAL GROUP by reading the wave number @ a peak.

wave number= no' of waves in 1 cm (units: cm^-1)

Used to:

IDENTIFY unknown compounds

determine the ABUNDANCE of isotopes in an element

gain info. on the STRUCTURE of molecules

detect POLLUTANTS and toxic chemicals

detect drugs

How it works:

Ionisation- molecules become +ve ions when electron is knocked off

Acceleration- molecular ions speed up

Deflection- ions deflected round a bend by magnetic field. Field strength required links directly to ion's mass

Detection- ions detected and info. fed to computor

m/z= mass:charge ratio

(charge always 1)

Molecular ion peak: furthest peak to the right of the graph

m/z value= Molecular mass

Fragmentation:

excess energy causes bonds to weaken

molecules split into 1 +ve ion and one neutral species

ions detected

neutral species aren't

Isomers have the same Mr but different fragmentation patterns