al., and the Aldrich Library of IR Spectra). Details of the correlation between IR patterns in these two regions and ring substitution are available in the literature references linked in the left frame (especially the books by Shriner and Fuson, Silverstein et. The pattern of the oop CH bending bands in the region 900-675 cm -1 are also characteristic of the aromatic substitution pattern. The pattern of overtone bands in the region 2000-1665 cm -1 reflect the substitution pattern on the ring. Not only do these bands distinguish aromatics, but they can be useful if you want to determine the number and positions of substituents on the aromatic ring. 2000-1665 cm -1 (weak bands known as "overtones").Compounds that do not have a C=C bond show CH stretches only below 3000 cm -1.Īromatic hydrocarbons show absorptions in the regions 1600-1585 cm -1400 cm -1 due to carbon-carbon stretching vibrations in the aromatic ring.īands in the region 1250-1000 cm -1 are due to CH in-plane bending, although these bands are too weak to be observed in most aromatic compounds.īesides the CH stretch above 3000 cm -1, two other regions of the infrared spectra of aromatics distinguish aromatics from organic compounds that do not have an aromatic ring: This is a very useful tool for interpreting IR spectra: Only alkenes and aromatics show a CH stretch slightly higher than 3000 cm -1. Note that this is at slightly higher frequency than is the CH stretch in alkanes. The = CH stretch in aromatics is observed at 3100-3000 cm -1. IR: aromatics IR Spectroscopy Tutorial: Aromatics
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