Abstract
This study presents a physics-based framework for understanding chemical reactions, highlighting the critical role of the occupied reactive orbital, the most stabilized occupied orbital during a reaction, in guiding atomic nuclei via electrostatic forces. These forces, termed reactive-orbital-based electrostatic forces, arise from the negative gradient of orbital energy, creating a direct connection between orbital energy variations and nuclear motion. Through the analysis of 48 representative reactions, we identify two predominant types of force behavior: reactions that sustain reaction-direction forces either from the early stages or just before the transition state. These forces carve grooves along the intrinsic reaction coordinates on the potential energy surface, shaping the reaction pathway. This clarifies which types of electron transfer contribute to lowering the reaction barrier. This study provides a framework for understanding the driving forces behind chemical transformations, offering insights into the electronic basis of reaction mechanisms.