Analysing IR spectrum.

IR looks at how infrared light interacts with a molecule, measuring the vibration of atoms. Bonds are continuously vibrating and moving around, much like two balls connected by a spring. This spring system is described by Hookes Law, frequency is proportional to the force constant (the stiffness of the spring). Therefore, an increase in bond strength an increase in frequency required to vibrate the bond. An IR spectrum usually consists of the fingerprint region - typically made up of the weaker bonds C-C, C-O etc. Double bonds are stronger due to a greater overlap of orbitals and therefore appear higher on the spectrum, similarly triple bonds are even stronger. Hydrogen bonds are very strong and therefore appear at a high frequency, however in a liquid each hydrogen bond is in a slightly different environment, therefore each have a very slightly different frequency - this (normally) gives the distinctive broad peak.