Carbon-carbon double bonds are the functional groups of alkenes and found in many natural substances as well as in commodity chemicals. Thus, the discovery of new methodologies for the construction of these bonds from readily available starting materials is in the heart of Organic Chemistry. In our project we developed a new method for the formation of carbon-carbon double bonds starting from two different aldehyde molecules. For this new synthetic procedure a phosphanylphosphonate reagent is used. An important part in the project is a mechanistic study of this particular coupling reaction. In order to support the proposed mechanistic steps and intermediates theoretically, we need to perform DFT calculations. For this purpose we need to run calculations for geometry optimization for different intermediate structures (small organic molecules), and calculate frequencies as well as some NMR chemical shift values. From the geometry optimization Gibbs free energy ΔG values can be extracted and compared in an energy diagram.
An important part for the investigation of the mechanistic intermediate steps and the observed stereochemical outcome is the finding of corresponding transition states that might be used as a theoretical support for the proposed mechanism.
 Keyhan Esfandiarfard, Juri Mai, Sascha Ott J. Am. Chem. Soc. 2017, 139, 2940-2943.