IR spectroscopy

infrared spectroscopy is used to

identify unknown chemicals by using infrared radiation to determine functional groups present in organic compounds

IR spectroscopy is used in conjunction with

nuclear magnetic resonance spectroscopy and mass spectroscopy to identify organic molecules

IR spectroscopy works as

covalent bonds have different strengths due to the masses of different atoms at either end of the bond, as a result the bonds vibrate at different frequencies and the frequency of the vibration can be found by detecting and recording when and how much the molecules absorbs EM radiation

from the absorbance measurements a

spectrum is produced which has characteristic curves for the different functional groups

the position of a peak depends on

bond strength and the masses of atoms joined by the bond, strong bonds and light atoms absorb at longer wave numbers, weak bond and heavy atoms absorb at high wave numbers

infra-red spectra are complex due to

the many types of vibration in a molecule

the fingerprint region is

on the right hand side from 500-1500 and it is unique for each species, containing tiny differences meaning its acts as the molecules fingerprint allowing it to be identified

the fingerprint regions is widely used in the analysis of the structure of

organic compounds as they tend to have a lot of C-C, C-H bonds which will be seen in the fingerprint region

the purity of a substance can be analysed using ir spectroscopy because

the presence of a strong absorption due to a C=O bond can tell if an alcohol has been oxidised to the equivalent carbonyl compound

on the IR spectrum graph

the x axis has frequency wavenumbers or wavelength, on the vertical axis there is absorbance

to use IR spectroscopy to identify compounds

compare the compounds IR spectrum with one on a computers database, the presence of certain absorptions can be used to identify functional groups

the functional groups IR spectroscopy can be used to identify are

O-H of an alcohol and carboxylic acid, the C=O of an aldehyde/ketone or carboxylic acid, C=C on unsaturated group

the O-H absorption for alcohols is

very broad absorbance with a range from 3200-3550

the O-H absorbance for carboxylic acids is

very broad, with a range from 2500-3300, it often has a tooth sticking out the right side

theC=C absorbance is

in the range 1629-1680

the C=O absorbance for aldehydes, ketones and acids is

strong and sharp with a range from 1640-1750

picture of infrared easier to identify

types of vibrations of bonds are

stretching (symmetric and asymmetric), bending

the greenhouse effect of a given gas depends on its

atmospheric concentration and its ability to absorb infrared radiation

the absorption of infra red radiation by atmospheric gases which

contribute to global warming