Structural Elucidation

Section Introduction
The determination of the chemical structure of organic compounds is an important aspect of chemistry in general and analysis in particular. Specialised spectroscopic instruments can be used to generate information that enables the determination of the structure of an unknown organic compound.

Structural elucidation can be thought of as putting together a jig-saw puzzle. A ‘chemical picture’ is constructed from the pieces of information (or clues) that are collected upon analysis of the sample by the various instruments.

The spectroscopic techniques that will be studied in this section are:

  • Mass Spectrometry
  • Infrared Spectrometry
  • Nuclear Magnetic Resonance Spectrometry

In the tasks that follow the different techniques are considered including the design of each type of spectrometer and its principle of operation. The main emphasis however will be on the interpretation of the spectra (i.e. information) that the instruments provide. The section concludes with exercises where you will synthesise such information to arrive at the chemical structure for a number of unknowns.

To determine structure, the compounds must be sufficiently pure, that is, a sample must consist essentially of a single organic compound not a mixture of different compounds. It can be assumed in this section that the sample preparation has been carried out to achieve the required level of purity.

There are four tasks you will be undertaking in this section.

  1. Mass spectrometry (MS)
  2. Infrared spectrometry (IR)
  3. Nuclear magnetic spectrometry (NMR)
  4. Structural elucidation in practice

Complete each task in order, following the steps and instructions.

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