Modern analytical techniques

Mass spectroscopy

Can be used to measure the molecular mass of molecules and the abundance of isotopes

Time of flight mass spec

  1. Vaporisation of atoms/molecules
  1. Ionisation of atoms/molecules
  1. Acceleration of ions
  1. Detection of ions

Peaks on a mass spectrum are caused by fragments of ions - this is because the atoms are bombarded by a stream of high-energy electrons, which knock an electron off the molecule

This forms a M+ ion (parent ion), which is unstable and breaks up into fragments, producing fragment ions and neutral fragments:
M+ (g) ----> F+ (g) + N(g)

The same molecules always fragment in the same way, allowing us to analyse them (fragmentation patterns help us identify molecules and their structure)

The M+1 peak is caused by the
presence of Carbon-13 in the molecule

It is usally found to the right of the M+ peak

The M+ ion peak is usually the heaviest mass/charge ratio (molecular mass of compound)

Infrared spectroscopy

Used to identify functional groups in a molecule

When molecules absorb IR radiation, their bonds vibrate and stretch (bonds vibrate at different frequencies depending on their strength and the mass of the atoms)

This stretching/bending results in a series of peaks

wavenumber = 1 / wavelength

speed of light (3.00 x 10*-8) = wavelength x frequency

Fingerprint region = 1500 - 500 cm-1
Can be used to identify 2 similar spectrums to see if they belong to the same compound