In a simpler time, one could ask: “What is the mechanism of the reaction?” Once asked, a chemist would develop a plausible model of the reaction and then devise experimental tests of that model. This continual modeling, testing, and then model refinement can lead to a deeper understanding of how a reaction takes place. That better understanding can aid the development of new methods of synthesis of desired compounds.
The reactions of interest to me involve compounds of carbon. The methods used to try to reach towards understanding are quite varied. If the reaction involves a short-lived intermediate or, perhaps, a series of intermediates, it proves useful to get the structural picture of that intermediate. If that can be accomplished, a significant step in the quest for understanding has been achieved.
One example of involves carbocation intermediates (very short lived, positively charged hydrocarbons) that have been the source of interest and debate for more than five decades. Model structures for these ions, if correct, provide an understanding of the results of experimental study, but they force the admission that some carbon compounds are formally pentavalent. This proposition required more tests. First, the means of preparing bulk quantities of these reactive intermediates had to be developed. Next some experimental means of examining these stabilized reactive intermediates at very low temperatures was required. Finally, to make the experiment work one had to use carbon compounds that were highly enriched with carbon-13 at specific sites. Students working with me did much of the synthetic work to produce the needed labeled compounds, and we were fortunate to have the collaboration of scientists at IBM who developed the instrumentation that allowed examination of the atom-by-atom structural detail of these compounds at temperatures as low as 5 K. The result was conclusive. One of the carbocations contained a pentavalent carbon. The other carbocation proved to actually be two structurally different intermediates with nearly the same energy and a very low barrier for interconversion.
Many other investigations found in the publication list were directed toward similar kinds of questions, but they were not as demanding of resources. Whether simple or sophisticated, the question: What is the mechanism of a reaction has importance. Answering the question can be difficult, but success is satisfying.