The abscissa of our IR diagrams shows the wavenumbers, and the boundary is at a value of 1500 cm‾¹. So we can also draw the lineat a value of 1500 cm‾¹ when we interpret spectrum. How will you distinguish these regions except the look of the peaks? Since the fingerprint region generally contains many signals and is more difficult to analyze, we can ignore it. It benefits us when we have similar compounds, for example, the same bonds (functional groups) but a different number of them. Such spectra will be the same in the diagnostic region, but in the fingerprint region won’t. Thus this region is called a fingerprint because each compound has a unique pattern of signals in this region, much the way each person has a unique fingerprint. Fingerprint region – contains signals resulting from the vibrational excitation of most single bonds ( stretching and bending).This region contains all signals that arise from all bonds in a molecule. Diagnostic region – generally has fewer peaks and provides the clearest information.IR spectra can be divided into two main regions: When the frequency of IR light matches the frequency of a particular vibrational mode, the IR light is absorbed, and you can tell which frequencies are absorbed by looking at your infrared spectrum. Different kinds of bonds vibrate at different frequencies, so they absorb different frequencies of IR light, so it is possible to determine the functional groups present.Īt first glance, the IR spectra look very complicated, but the only three things you need to know are: We call that a stretchingor bending vibration. These vibrations occur only at specific frequencies, which correspond to the frequency of IR light. Absorbed energy can cause a bond to stretch or bend. If you shine infrared light on a molecule, it is possible that the molecule absorbs energy from light. Infrared (IR) spectroscopy is a very useful method for detecting the characteristic bonds of many functional groups through their absorption of infrared light.
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