Predict the number of peaks in the infrared spectrum of a molecule by observing how many vibration modes change the molecule’s dipole moment. If a vibration mode changes the dipole moment, that mode will be responsible for a peak in the infrared spectrum. For advanced classes, character tables can be used to verify predictions about infrared activity. Infrared active vibrations have the same symmetry as the Cartesian coordinates x, y, and z.
Some good molecules to consider are those structures that were determined using electron diffraction.