Dr. Frank De Proft - Influence of Mechanical Force and External Pressure on Chemical Reactivity

Mechanical activation of single molecules and the application of external pressure to activate chemical processes have attracted much attention recently. Important questions emerging are “where” to apply a mechanical force and “what” happens to chemical reactivity upon application of mechanical forces and pressure. We aim at answering these questions for simple systems within the framework of conceptual density functional theory. Conceptual Density Functional Theory (CDFT) has emerged as a very successful theory of chemical reactivity. In CDFT, chemical concepts and reactivity indices are most often introduced as response functions of the energy E of the system with respect to variations in either its number of electrons N, its external potential v(r) or both. By stretching diatomic molecules, the responses of reactivity indices were investigated. The effect of straining bond angles was probed for linear and cyclic alkynes, bridging the concept of ring strain and mechanochemistry. Upon bending, the reactivity of the triple bond increases which is reflected in faster click reactions between cyclic alkynes and azides, as compared to the linear alkynes. [3] Next, we explored the mechanical activation of more challenging systems by quantifying the changes in the potential energy surfaces induced by mechanical stress. As an example, we discuss the circumvention of the Felkin- Anh diastereoselectivity upon stretching the ketone with a mechanical pulling force. In a final part, we investigate the effect of pressure on atomic chemical concepts, such as the electronegativity, hardness and electrophilicity