It is important to determine how well your reaction has worked, both in terms of the amount of product you have isolated (and purified where appropriate), and in terms of the overall use of chemicals during the reaction and workup. Energy use should also be taken into account, as this is increasingly expensive and environmentally damaging, but we are not going to look at this here. 

There are dozens of metrics that are available to measure the performance of a reaction/ process, and these vary from the very simple to the very complex. Generally, the more complex the metric, the more detailed the data required, much of which is unlikely to be available without a considerable amount of extra work. The outcome of this is that these metrics are rarely used. 

Simple metrics are easy to use and are widely applied, even though they may have several over-simplifications which must be borne in mind. In this year’s practical sessions we will use the three commonest metrics, Atom Economy (AE), percentage yield, and Process Mass Intensity (PMI).   An excellent overview of metrics is provided by the Chem21 project website, generated by several university research groups (including the Green Chemistry Centre of Excellence) and several pharmaceutical companies.