FTIR+spectroscopy

The acronym FT-IR refers to Fourier Transform Infrared Spectroscopy.

Infrared spectroscopy is used in the identification of functional groups within an organic compound, which can help in the identification and structural elucidation of that compound.

A molecule's covalent bonds are not rigid. They flex, vibrate, oscillate, and twist. All of these motions happen at certain frequencies, just like the sound waves from strings of a guitar, piano, or tuning fork. These motions are referred to as vibrational modes.

The frequencies at which these modes resonate lie within the infrared portion of the electromagnetic spectrum. When IR radiation is passed through a sample (usually embedded in a potassium bromide crystal), absorption of this radiation occcurs at specific frequencies that relate to certain covalent bond vibrational modes. These frequencies are then referred to a list of known values for functional groups, and can help identify the presence of functional groups and bonds in a molecule.

Here is a chart depicting the vibrational mode frequencies for some organic functional groups.

Take a look at some sample FT-IR outputs. The first is of vanillin, an organic compound found in vanilla extract.

There are plenty of peaks, so finding the important ones is a skill that takes some experience. Note these peaks, from left to right:
 * 3500 cm-1: due to the hydroxyl functional group (part of the phenol group)
 * 1700 cm-1: due to the C=O bond in the aldehyde fg
 * 1600 and 1500 cm-1: C=C bonds in the aryl fg
 * 1000-1300 cm-1: C-O bonds in the ether fg

Here is the IR spectrum for butanal, with the key functional group peaks labeled.

Note the region called the "Fingerprint" region - this is an area of most spectra where the peaks tend to blend and not provide clear, identifiable peaks.

Here are a few more to take a look at for fun.