Spectroscopy

Mass Spectrometry• These are used to

measure the masses of atoms and molecules with great accuracy.

• They are also capable of detecting very small quantities of a substance (less than 10-6g)

Mass Spectrometry

Mass Spectrometry

• Mass spectrometry can be used to detect different isotopes of elements. The data can then be used to calculate RAMs.

• It can also be used to identify compounds by looking at fragmentation patterns.

Mass Spectrometry (elements)

Mass spectrum for Boron

Mass Spectrometry (fragments)

UV-Visible Spectroscopy• An absorption

spectrum is produced. Certain wavelengths are absorbed better than others. In coloured solutions e.g. transition metal solutions the colours which are less well absorbed give rise to the colour we see.

Ultra-violetViolet

Orange

Infra-Red Spectroscopy

• IR energy excites bonds in compounds making them vibrate more energetically.

• It can be absorbed when the energy matches the difference between the vibrational energy levels belonging to the bonds.

• The y axis indicates % transmission of energy, so when energy is absorbed the spectrum will show a trough.

• The x axis is wavenumber, high wavenumber indicates high energy.

Infra-Red Spectroscopy

http://www.cem.msu.edu/~parrill/AIRS/name_list.html

This band at around 3300cm-1 is due to O-H stretching

This band at around 1150cm-1 is due to C-O stretching

Nuclear Magnetic Resonance (NMR)

• This type of spectroscopy detects hydrogen atoms (in the main).

• Hydrogen atoms have a nucleus that has a net spin and therefore can be detected

• An NMR spectrum can tell us what type of environment a hydrogen atom is in and how many there are.

NMR

There are 5 hydrogen atoms in a similar environment i.e. attached to the ring

There are 3 hydrogen atoms in the CH3 group

A chemical shift of 7.3 is typical for aromatic compounds

A chemical shift of 2.3 corresponds to a CH3 group attached to a benzene ring

X-Ray Diffraction

• X- Rays are diffracted from the layers of atoms or ions in a crystal

• The intensity of the spots on an X-Ray diffraction photograph can be analysed and used to build up an electron density map of an entire molecule

X-Ray Diffraction

X-Ray diffraction photograph

Computer simulated electron density map