Structure Determination of Organic Compounds

STRUCTURE DETERMINATION OF ORGANIC COMPOUNDS

STRUCTURE DETERMINATION

Because of the wide variety of reactions available to synthetic chemists, it is possible to devise synthetic strategies for just about any target that we wish.

Nevertheless the planning and execution of any synthesis must be verified by showing that the product of each step is in fact the predicted compound and that the target compound was actually obtained. Thus a critical part of any synthesis involves determining and proving the structures of synthetic intermediates and final products. While the majority of the time careful planning will result in the formation of the expected product, there are always enough exceptions to make structure proof an imperative step.

In earlier times, proof of structure was based largely on wet methods. The first step was to rigorously purify the compound by crystallization, distillation, subli-mation, and so on. The functional groups present in the material were established by classification tests. The elemental analysis gave the molecular formula, and from a knowledge of the starting materials, a tentative structure could be writ-ten. Confirmation of the structure was obtained by either degradation to known compounds or an alternative synthesis of the compound from known starting materials. Thus, while the presence of functional groups could be determined rather straightforwardly, the connectivity of atoms and groups in a molecule were much more difficult to establish.

Today structure proof involves the same components— purification, functional group identification, and establishment of atom and group connectivity; however, the ways in which these are accomplished are more efficient, sensitive, and reli-able. They are also much faster. The ability to run reactions, purify products, and determine structures on milligram scales, often in a matter of hours, has caused a huge increase in the rate at which structural information can be obtained. This has resulted in an exponential growth of chemical knowledge and is directly responsible for the explosion of information being continually published in the chemical literature.