Spectroscopic Identification of Organic Compounds

Basic Principles

Spectroscopy is a technique used to detect and identify the atoms and molecules in a substance.
Organic compounds can be identified spectroscopically by their unique interaction with electromagnetic radiation. This interaction depends on the chemical structure of the compound.
Different types of spectroscopy are used to identify different features of organic compounds, such as their functional groups, structure and molecular geometry.

NMR spectroscopy reveals the hydrogen and carbon structure of an organic molecule.
It involves aligning the magnetic moments of certain atoms in a magnetic field and detecting the response to absorption of radio frequency radiation.

IR spectroscopy measures the absorption of infrared radiation, which causes molecular vibrations.
It is extremely useful in identifying functional groups present in an organic molecule.

Mass spectroscopy reveals the mass-to-charge ratio of ions, helping in determining molecular mass.
It can also provide detailed information about the molecular structure of an organic compound.

In NMR spectroscopy, different hydrogen environments within an organic compound appear at different positions on the spectrum. The area under each peak is proportional to the number of hydrogens in that environment.
In IR spectroscopy, different functional groups absorb IR radiation at specific wave numbers. By matching these values to reference tables, the functional groups present can be determined.
In mass spectroscopy, the spectrum shows the mass-to-charge ratio of detected ions. The most intense peak (the base peak) often comes from the most stable ion.

Spectroscopy requires clean samples and careful preparation to minimise potential sources of error.
It is a destructive technique, which might not be suitable when sample size is limited.
Complex mixtures may produce complicated and overlapped spectra, making interpretation challenging.
It’s imperative to use multiple methods of spectroscopy for a more reliable identification.

Spectroscopy complements other techniques in organic chemistry by providing a physically based set of data.
This data, combined with chemical reactivity and other tests, gives a more complete understanding of the structure and properties of organic compounds.