One of the tools available to organic chemists to determine whether a reaction has occurred, or to determine the structure of unknown compounds is infrared spectroscopy (IR). In an IR spectrum the absorbance of energy at characteristic frequencies and with characteristic intensity can be used to determine the presence of functional groups that absorb energy at that frequency. Since this is a low energy radiation source, the molecule is not changed structurally; the energy absorbed causes bond vibrations and bond bending. Since the absorbance of energy that causes the bonds to bend and vibrate changes with the type of bond, this is a useful method for determining the presence of functional groups within a molecule. The IR below is shown as the amount of light transmitted by a sample as a function of frequency of the incident IR radiation. Using the table of IR absorbance frequencies in your text book evaluate the IR spectra below and choose which structure best fits the data.
