In: Chemistry
IR means infrared spectroscopy.
Spectroscopy is the study of interactions of radiations with matter.
IR uses the infrared region of electromagnetic radiations to study it's interactions with chemical Substance. Apparently IR is used to identify the functional groups present in the unknown compound.
It is based on principle that molecule absorb frequencies of light that are characterstics of their structure. These absorption frequencies occur at frequency which matches vibrational frequency.
IR frequency is measured in cm-1.
Different modes of vibrations are there.
A spectrograph is prepared by drawing absorbance or transmittance on vertical axis and frequency along horizontal axis.
Two regions for IR are
Functional group region 4000, to 1500 cm-1
Fingerprint region less than 1500 cm-1
Example
O-H have stretching mode of vibration in functional group region at around3600- 3400 cm-1, if spectrum has peak in this range means OH present in compound