We have already studied the IR spectroscopy of both these functional groups, so we can take a stab at predicting what their spectra might look like. Note that ester groups contain one C=O bond and two C-O bonds. Finally, esters are amongst the flavoring agents in foods and are used as solvents. Fat molecules contain many ester linkages. Polyesters are important materials made into beverage bottles, fabric, and clothing. I observed that the natives were fond of dropping the r's at the end of words, as exemplified in the hackneyed phrase, 'Pahk the cah in Hahvahd Yahd.' Not surprisingly, I heard native New Englanders consistently call this functional group an 'estah.'Įsters are industrially and biochemically important. I am not originally from New England, but I did live there for a number of years. As we will see in the next two columns, IR spectroscopy can easily distinguish saturated from aromatic esters.Ī word on the pronunciation of this functional group is in order. If the alpha carbon is saturated, it gives a saturated ester, whereas if the alpha carbon is aromatic we have an aromatic ester. The carbon to the left of the carbonyl carbon in Figure 1 is called the alpha carbon, and the oxygen to the right is called the ester oxygen. The carbon in the C=O group in esters is called the carbonyl carbon, as has been the case in all the other carbonyl containing functional groups we have studied (1–5). The molecular framework of the ester functional group is shown in Figure 1.įigure 1: The molecular framework of the ester functional group. My high school chemistry teacher (who in large part was responsible for my career choice) helped us remember the name of this reaction by pronouncing it 'ester vacation' and saying it was the time off we got from school around Easter. If an alcohol and a carboxylic acid are reacted a functional group called an ester is synthesized. Acid anhydrides and carboxylates are both made from carboxylic acids. So far in our investigation of the infrared (IR) spectroscopy of the carbonyl functional group we have looked at ketones, aldehydes, carboxylic acids, acid anhydrides, and carboxylates (1–5). The spectra of saturated and aromatic esters will be examined over the next two columns. All esters exhibit three intense peaks and hence follow what I like to call the Rule of Three. Esters are very common and are economically and biologically important. Like acid anhydrides and carboxylates, esters are made via a reaction involving carboxylic acids. The sixth installment in our examination of the infrared spectroscopy of the carbonyl group is focused on esters.

Amide ir spectrum