Organic chemistry, a fundamental pillar of our understanding of carbon-based molecules, has just undergone a major revolution. A rule established a century ago, until then considered incontestable, turns out to be erroneous. This discovery, published in the journal Sciencecould open doors for manufacturing molecules once thought impossible to produce, with potentially significant implications in areas such as medicine and synthetic materials.
The principle of Bredt’s rule
Given its adaptability, carbon is present in almost all compounds, including us, which are primarily made up of molecules with a carbon structure. Carbon is capable of making four bonds – single, double or triple – with other carbon molecules, a characteristic that allows it to form a wide variety of molecules.
Since 1924, Bredt’s rule has served as a benchmark in organic chemistry. By observing hundreds of molecules, Julius Bredt established that, in certain specific structures, double bonds were impossible. When two carbon rings join to form a bridge, he had observed that the junction point could not be associated with a double bond, as this seemed to make the structure unstable. This hypothesis, confirmed by the absence of such bonds in molecules of this type observed for decades, took root in textbooks and became a rule tacitly accepted by the scientific community.
Bredt’s rule has long been a standard, integrated into chemistry courses and recognized by reference organizations such as the International Union of Pure and Applied Chemistry (IUPAC). While this rule underwent some adjustments – admitting that double bonds could exist in larger ring systems – it remained valid for smaller structures. However, new research carried out by Professor Neil Garg’s team at the University of California, Los Angeles (UCLA) reveals that this rule could be much more flexible than Bredt and his successors had envisaged.
Anti-Bredt molecules
By defying Bredt’s rule, Neil Garg and his colleagues succeeded in producing molecules containing double bonds in cyclic bridge structures, calling them “anti-Bredt olefins” (or ABO for Anti-Bredt Olefins). These molecules are amazing, because they technically shouldn’t exist according to the principles of classical organic chemistry.
To produce these ABOs, the research team used an innovative method, applying fluoride to specific precursors called silyl pseudohalides. Although the first versions of the ABOs produced turned out to be unstable, researchers were able to stabilize them using various agents, thus allowing their analysis and potential applications.
This advance marks a decisive moment for chemists, because it shows that three-dimensional structures, previously ignored for their supposed instability, could be exploited. “ The pharmaceutical industry is working to develop chemical reactions that produce three-dimensional structures like ours because they can be used to discover new drugs said Mr. Garg.
The limits of observation in science
The work of Neil Garg’s team raises a question: to what extent can rules based on observations hinder scientific creativity? Indeed, for decades, chemists did not seek to create molecules like anti-Bredt olefins, not out of lack of interest, but because they believed it simply was not possible. The existence of an established rule, perceived as insurmountable, has therefore restricted experimentation and research in this area.
According to Garg, it is crucial that rules derived from observations are viewed cautiously, as guidelines rather than absolute limits. Chemistry, like other sciences, often progresses by challenging established conventions.
Besides, are you good enough at chemistry to associate these elements with their symbol?
