Combining spectroscopic techniques (6.3.2)

Different analytical techniques can provide different details about the structure of a molecule. By combining the different strands of evidence from different techniques a more complete description of the molecule can be obtained.

• The NMR spectra gives information about the molecular structure and arrangement of atoms, especially hydrogen () and carbon () atoms.
• The IR spectra helps identify functional groups within a molecule based on their characteristic bond vibrations.
• The mass spectra provides the molecular weight and details on sections of the molecule through the fragmentation pattern.
• Chemical tests involve observed changes and behaviour when molecules undergo chemical reactions. This can often involve colour changes and other observations that are characteristic of different functional groups or component ions.

Analytical results can be interpreted individually, then pieced together.

First try and establish the and molecular formula, which usually come from elemental analysis and mass spectroscopy.

Then identify functional groups, usually via qualitative analysis and IR spectroscopy.

NMR is then useful for identifying the relative positions of the molecular components identified. Structural arrangement of isomers comes through analysis on NMR spectrum.