IR (Infrared) Spectroscopy is used for determining the presence or absence of a wide variety of functional groups in a molecule. One way to begin analysing an IR spectrum is to start at the high wavenumber end of the spectrum (typically 4000 cm-1) and look for the presence and absence of characteristic absorptions as you move toward lower wavenumber.
There are two regions of IR spectrum, one is called functional group region (range : 4000 - 1600 cm-1), another is finger print region (1600 - 400 cm-1)…In functional group region we can find individual peak at specific wavenumber, and can match this data with reference list (find on google )
The absorption wavenumber for a stretching vibration is related to both the force constant between the two atoms (k) and the mass of the two atoms (m1 and m2) by the Hooke's Law equation:

From this relationship, two important trends in the wavenumber for stretching vibrations can be deduced.
1. As the bond strength increases, the wavenumber increases.
2. As the mass of one of the two atoms in the bond increases, the wavenumber decreases.
* Wavenumber also depends on conjugation : More conjugation = less wavenumber
Intensity of Absorption
The intensity of an absorption in the IR spectrum is related to the change in dipole that occurs during the vibration. Consequently, vibrations that produce a large change in dipole (e.g. C=O stretch) result in a more intense absorption than those that result in a relatively modest change in dipole (e.g. C=C). Vibrations that do not result in a change in dipole moment (e.g., a symmetrical alkyne C triple bond C stretch) will show little or no absorption for this vibration.
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29 янв 2019
