CH 2-4 Example: Using Infra-Red (IR) Spectroscopy to ID an Unknown Compound IR is an instrumental method used to identify some of the functional groups present in an organic compound. The x-axis scale represents frequency in wavenumbers, and runs from 4000 - 600 cm-1

The absorption bands of different functional groups absorb at different frequencies and intensities. (~3300 if terminal) Keep it simple! Do not memorize the absorption frequencies, and do not “over-interpret” the IR spectrum. Focus on these four specific functional group(s).

Example #3: Unknown Structure Identification Formula: C5H10O Additional Info: Three, 1o carbons One, 3o carbon Calculate Hydrogen Deficiency Evaluate IR spectrum Suggest possible structures

Example #3: Unknown Structure Identification Formula: C5H10O Additional Info: 3x1o carbons; 1x3o carbon HD = 2 IR = carbonyl: C=O