EXPRESS: A Divide-and-conquer Approach that Guides Undergraduate Students in the Interpretation of Organic Infrared Spectra

A divide-and-conquer approach is presented that helps undergraduate students interpret organic infrared-spectra. In this method, DivnConqIR , students deal with the confusion of a complicated spectrum by focusing first on the carbonyl band at ∼1720 cm -1 near the middle of the spectrum. When present, its position and related bands can be analyzed to determine the specific functional group to which the carbonyl belongs; in its absence, students eliminate many functional groups. In either case, students begin spectral interpretation with significant accomplishment. This strategy divides the spectrum again, now at 3000 cm -1 , to define the backbone of the organic molecule and determine the possible presence of alkenes, alcohols, amines, or terminal alkynes. Students divide the spectrum again, now at 1375 cm -1 , to confirm the presence of methyl group(s) with the methyl umbrella band or, if present, isopropyl or tert -butyl doublet bands for further connectivity. Students divide the spectrum again, now at 1000 cm -1 , to search for the presence of one or more C−O stretches and to confirm the presence of alcohols, carboxylic acids, esters, or anhydrides, or to discover ethers. Lastly, students use DivnConqIR to examine unaccounted bands to identify other useful functional groups that may be present. Students interpret IR spectra without confusion and determine functional groups effectively; they integrate functional groups into possible complete structures. Qualitative and quantitative student performance data are offered to suggest the effectiveness of this interpretive approach, and DivnConqIR is compared to other IR interpretation methods to show that it is unique and most comprehensive. Many worked examples are presented, and additional resources are provided.