Introducing a simplified model of frontier molecular orbital theory as a pre-organic foundations module for high school students in advanced programs

Abstract Students in A-Level and IB, and similar high-school curricula are expected to understand nucleophilic substitution mechanisms (S N 1 and S N 2), yet many rely on memorization because curricula do not provide a conceptual bridge between quantum concepts taught early and organic mechanisms taught later. A survey of 138 Vietnamese high-school students over 28 high schools confirms this gap: about 70 % find chemistry difficult, nearly 55 % memorize mechanisms, and nearly 60 % consider organic chemistry harder than inorganic chemistry. Notably, more than half of the students have at least heard of Frontier Molecular Orbital (FMO) theory, indicating readiness for conceptual instruction. To address this need, we propose a five-period high-school module introducing FMO theory as a bridge between atomic orbitals and organic reaction pathways. By emphasizing HOMO–LUMO interactions, the module helps students rationalize S N 1/S N 2 mechanisms rather than memorize them. A pilot implementation with 10 students showed improved mechanistic reasoning and decreased reliance on rote learning. The approach aligns with IB skill-development frameworks and offers a feasible strategy for enhancing conceptual understanding in modern chemistry curricula: the bridge AO → MO → FMO → Mechanisms.