![]() ![]() Since all ethers contain a C-O-C linkage, the vibration that we would usually refer to as a “C-O” stretch actually involves the asymmetric stretch of the C-O-C moiety as shown in the left side of Figure 2. If both ether carbons are saturated then we have a saturated ether, if both ether carbons are aromatic that gives an aromatic ether, and if one ether carbon is saturated and one is aromatic it is a mixed ether. Here we discuss three different types of ether, which are characterized by the type of carbons attached to the central oxygen. In fact, the only useful group wavenumbers for ethers are their C-O stretching peaks as discussed below. Because ethers do not contain an -OH bond there is no significant hydrogen bonding and there are no -OH stretching or bending peaks. The carbons in these bonds are referred to as ether carbons as shown in the figure. Note that unlike alcohols ethers contain not one but two C-O bonds. Ethers are characterized by a central oxygen atom with two carbons attached, as shown in Figure 1. Now that we are finished with these molecules the next functional group to study that contains the C-O bond is ethers. Also note the carbon-carbon stretches in the aromatic ring (1614, 1506, 1465), the in-plane CH bending (1086, 1035), and the CH oop (738).We discuss three different types of ether, which are characterized by the type of carbons attached to the central oxygen.Ī few issues ago we started our survey of the infrared (IR) spectroscopy of the C-O bond (1), and proceeded to study the spectra of alcohols and phenols (1,2). The characteristic overtones are seen from about 2000-1665. Note the =CH stretches of aromatics (3099, 3068, 3032) and the ≬H stretches of the alkyl (methyl) group (2925 is the only one marked). If you are presented with two spectra and told that one is aromatic and one is not, a quick glance at the sheer multitude of bands in one of the spectra can tell you that it is the aromatic compound. In some instances, it is useful to remember that aromatics in general show a lot more bands than compounds that do not contain an aromatic ring. 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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