Amide ir spectrum1/4/2024 There is some orbital overlap here, as illustrated in Figure 3, which leads to conjugation. This orbital happens to point in space towards the pi-electron cloud of the carbonyl group. The nitrogen atom in amides contains a p-orbital with a lone pair of electrons in it. Spectroscopically, this is expressed as a ~30 cm -1 lowering of the position of the C=O stretch compared to a non-conjugated carbonyl (3), and we spoke of saturated and aromatic versions of carbonyl containing functional groups (3).Īmides also engage in conjugation as seen in Figure 3. Briefly, the pi orbital on the carbonyl group overlaps slightly with the pi electron cloud orbital on the aromatic ring, causing a small amount of electron density to be withdrawn from the carbonyl bond lowering its force constant. In previous columns when we studied carbonyl groups attached to benzene rings, we encountered the phenomenon of conjugation (3). Therefore, when looking at the structures of amides, amines, and other nitrogen containing functional groups, a primary nitrogen will have one C-N and two N-Hs, a secondary nitrogen will have two C-N bonds and one N-H, and a tertiary nitrogen will have three C-Ns and no N-H bonds. Given that this primary/secondary/tertiary terminology applies to both amines and amides, we can speak more generally of primary, secondary, and tertiary nitrogens. Thus, a primary amide has one C-N bond and two N-H’s, a secondary amide has two C-N bonds and one N-H, and a tertiary amide has three C-N bonds and no N-H bonds. Note that, as in amines, we are counting the number of C-N bonds. The skeletal frameworks of primary, secondary, and tertiary amides are seen in Figure 2. Similarly we speak of primary, secondary, and tertiary amides, and again the difference between them is the number of carbons attached to the nitrogen. When we first started studying organic nitrogen compounds and were introduced to amines, we found that they came in three varieties, called primary, secondary, and tertiary, depending upon the number of carbons attached to the nitrogen atom (2). This nitrogen is called the “amide nitrogen”, and can have carbons or nitrogens attached to it. The amide functional group consists of a central carbonyl group with a nitrogen atom single bonded to the carbonyl carbon. My preferred pronunciation is “Ay-mides”, which I will use throughout the rest of this column. The first thing we have to decide is how to pronounce the word “amide.” Depending upon who I am talking to and where they are from, I have heard about nine different pronunciations for this word that, when spelled out phonetically, are: Ay-mids, Ay-mides, Ay-muds, Uh-mids, Uh-mides, Uh-muds, Am-mids, Am-mides, and Am-muds.
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