Abstract: How do we know what we say we know? In synthetic chemistry, there are tools we use which give us data from which we can deduce details of a molecule’s structure. Many of these tools are spectroscopic in nature and some rely on changes in how a molecule rotates, vibrates, how its electrons are distributed, or even how individual types of nuclei spin. There are also methods based on diffraction that can yield a “snapshot” of a molecule’s structure. This talk will be from a synthetic perspective, i.e. how do we make sure that what we tried to make is what we actually made, and what sort of purity did we achieve?