Topic 7 - Modern Analytical Chemistry

• The infared spec is between 800-10000nm
• Bonds are constantly vibrating, the absorption of IR radiation causes them to become excited
• Bonds can shift in different ways, causing there to be a range in absorption
• Only vibrations that produce or change dipoles can be observed
• Wavenumber is proportional to the energy of the vibration
• The fingerprint region is a complicated region with lots of small peaks
• Each molecule has a different fingerprint region and this can be used to identify it against other molecules with the same functional groups
• The IR spec is good for identifying impurities
• When organic compounds are ionised for mass spec they can split into smaller organic compounds
• If a molecule is put through a mas spectrometer it will fragment into smaller molecules
• The largest m/z peak is the molecular ion peak
• C-C bonds are the most common to fragment as carbocations are relatively stable
• The fingerprint region is a very complicated region unique to each different type of molecule
• Using an infared spec, you can identify bonds in molecules
• Only molecule that can change their polarity are picked up on the infared spec
• Diatomic molecule do not get picked up by infa red spec as the bonds do not change polarity when vibrating