9.1 Introduction
The determination of structure of an organic compound requires specialized techniques. In the past, such techniques were laboriously time consuming and sometimes unreliable too. Modern technology has sorted out this difficulty with the advent of spectroscopic methods for determination of structure.
Spectroscopy is the study of interaction of electromagnetic radiation with matter. As the electromagnetic spectrum consists of radiations of different wavelengths, the responses of the molecules to these wavelengths differ. Thus, X-rays are scattered by the molecules, infrared radiation cause bonds in molecules to vibrate and radio waves make nuclei of atoms to resonate. Spectroscopy measures these interactions and a correlation is obtained between these interactions and molecular structure.
In this section, four major spectroscopic techniques are discussed.
- UV-visible
spectroscopy : It can provide information about the presence of unsaturation in the molecule as well as the presence of certain functional groups.
- Mass spectroscopy : This can give information about the molecular weight of the molecule and its composition in terms of elements.
- NMR spectroscopy : It can reveal a lot of information about a molecule and is by far the most widely used technique in organic chemistry. It can reveal information about the carbon skeleton, the number of protons attached to each carbon as well the number and position of certain other elements.
- Infrared spectroscopy : It is used to determine the presence of certain functional groups in the molecule.