Worked Examples

Abstract

There is no fixed way of tackling a problem in structure determination using the four spectroscopic methods. Each problem has its own unique features, and some knowledge of the provenance makes a big difference to how one starts. At one extreme, the product of a reaction with known starting materials is often predictable, and the purpose of the spectroscopic investigation is largely to check that the compound actually isolated does have the expected structure. On the other hand, a complete unknown, extracted from a plant for example, will have little information to be drawn on. In the former case one must guard against a too easy assumption that the predicted structure fits the spectra; in the latter one can only draw on one’s knowledge of the known structures of natural products—often of limited use since these are astonishingly diverse. In the discussion that follows, we work through some representative examples in which provenance is missing. This is not all that realistic, since compounds handled in research rarely have so little information attached to them, but these examples will serve to show how one can go from one spectrum to the next to draw out all the information needed in order to assign a structure. The sequence we use here to put together the pieces of spectroscopic information in order to deduce the structures is by no means the only one that would work, or even necessarily the shortest. We hope that what we do serves to show how expeditiously the various leads can be connected.