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➢ IR spectrum
The IR spectrum is a graph where the x-axis is frequency and is labelled as wavenumber (cm ).
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The y-axis is the amount of light transmitted and labelled as transmittance (%). This is measuring
how much light has been transmitted at a particular frequency. In other words, if all of the light is
detected, then the molecule has absorbed no light at that frequency.
➢ Nature (intensity & shape) of spectral bands:
• IR bands can be classified as strong (s), medium (m), or weak (w), depending on their
relative intensities in the infrared spectrum.
• A strong band covers most of the y-axis. A medium band falls to about half of the y-axis,
and a weak band falls to about one third or less of the y-axis.
• According to shape, IR bands can be classified into broad and narrow (or sharp).
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