Teaching Acyclic Conformational Preferences with Density Functional Theory Calculations and Natural Bond Orbital Analysis: An Undergraduate Organic Chemistry Laboratory Module

Conformational analysis is a foundational yet conceptually challenging topic in organic chemistry education, critical for understanding molecular structure, stereochemistry, and noncovalent interactions. This laboratory module guides undergraduate students in conformational analysis of ethane, 1,2-dichloroethane, and 1,2-difluoroethane using density functional theory (DFT) calculations and natural bond orbital (NBO) analysis. Through potential energy surface (PES) scans, molecular orbital visualization, and second-order perturbation theory analysis in NBO, students investigate stereoelectronic factors such as hyperconjugation, while also considering the role of steric repulsion in conformational preferences. These activities promote the development of skills in constructing and interpreting energy profiles, analyzing orbital interactions, and reasoning about electronic and steric contributions to molecular stability. Pre- and postlaboratory assessments, along with student surveys, revealed substantial gains in conceptual understanding, computational proficiency, and representational competence. Students also expressed increased confidence and interest in applying computational tools to a broader range of chemical problems. The flexible and scalable design of this module offers a practical framework for integrating modern computational methods into undergraduate organic chemistry instruction.