![]() ![]() Peak B at 904 is the asymmetric C-O-C stretch, and peak C at 831 is the symmetric C-O-C stretch. Note that this falls in the range where C-O stretching peaks traditionally fall. Peak A at 1261 is the symmetric ring breathing vibration. The spectrum of an epoxide is seen in Figure 3. The peak from this vibration is found from 880–750. The third vibration illustrated in Figure 2 is the symmetric C-O-C stretch, where the two C-O bonds stretch while the C-C bond contracts. The peak from the epoxide asymmetric C-O-C stretch appears from 950–810. The vibration illustrated in the center of Figure 2 is called the asymmetric C-O-C stretch, where one C-O bond stretches and the other contracts, similar to the asymmetric C-O-C stretch of ethers (3). The peak for this vibration falls from 1280–1230, in the range where we normally see C-O stretching vibrations. As you can see, all three bonds in the ring stretch and contract in phase with each other, as though the ring were exhaling and inhaling. The left most vibration illustrated in Figure 2 is called the epoxide symmetric ring breathing vibration. The S in Figure 2 means a bond stretches during that vibration, and a C means a bond contracts during a vibration. ![]() Figure 2 shows three stretching vibrations for the epoxide ring. However, epoxies are the first ring systems we have studied that have C-O bonds in them, and they follow our 1300–1000 rule. We have learned previously when we studied the spectra of alcohols and ethers that C-O stretching vibrations have strong peaks from 1300 to 1000 cm -1 (going forward all peak positions will be in cm -1 even if not noted) (2). Epoxides are monomers that react via ring opening reactions to form the sticky stuff we are familiar with.įigure 1 shows that an epoxy ring contains two C-O single bonds. ![]() The bond angles in an epoxy ring are less than optimal, creating what is called ring strain, which means these rings are unstable and undergo ring opening reactions easily. We know that carbon prefers to form single bonds with bond angles of approximately 109.5° (1). The structure of the simplest epoxide, ethylene oxide, is seen in Figure 1. We bandy about this word a lot, but what is an epoxy anyway? An epoxide is a molecule that contains an epoxy ring, which is a three-membered ring containing two carbons and one oxygen atom (1). The Epoxy GroupĮpoxy resins are used so commonly that the word “epoxy” has entered the English language as a word that refers to a large group of glues and adhesives. Probably the most important polymers in this group are epoxies and epoxy resins, which are widely used as adhesives. Here, we begin a series on polymers containing C-O bonds, and after that, we will discuss polymers with C=O bonds.Ĭompared to the polymer families containing C-H and C=O bonds, the family of C-O containing polymers is small for reasons I do not understand. The last four installments were devoted to polymers that contain C-H bonds. Now that we are five columns into our examination of polymer spectra, you may have noticed that these articles are structured similarly. In the first five or so years of this column, there were multiple columns devoted to functional groups containing C-H, C-O, and C=O bonds. The answer to last column’s Infrared Spectral Interpretation workshop will also be given.Īs you probably noticed, the organization of this column series has been divided into sections based on specific chemical bonds. In this column, the spectra of epoxides and the reaction via which they become useful is examined. Epoxy resins are widely used as adhesives, and you may have used them yourself to mend broken household items. As we begin our survey of the infrared (IR) spectra of polymers containing C–O bonds, we discuss epoxies, perhaps the most economically important functional group in this category. ![]()
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