Multicolor 3D-Printed Molecular Orbital Models for a First-Semester Organic Chemistry Course

We have developed a set of multicolor 3D-printed structural and molecular orbital models for use in a first-semester organic chemistry course. These models provide visual and tactile insights regarding aspects of organic structure, reactivity, and mechanistic “arrow pushing”. The set includes: 1. orbital models of σ and π bonding in methane and ethylene, 2. σCH–σ*CH hyperconjugation in staggered and eclipsed ethane conformations, 3. LUMO accessibility in SN2 electrophiles and HOMO–LUMO orbital interactions in SN2 transition states, 4. E2 transition state structure and orbital interactions in β-hydrogen removal and π bond formation, 5. σCH–pC hyperconjugation in the ethyl cation, 6. transition state structure and σCH–pC orbital interactions in a carbocation 1,2-hydride shift, 7. late and early, respectively, Br• and Cl• H atom radical abstraction transition state structures and SOMO orbitals, 8. bromonium ion structure and LUMO orbital, 9. protonated epoxide ion and neutral epoxide structures and LUMO orbitals, 10. transition state structure and orbital interactions in a hydroboration reaction, 11. transition state structure and orbital interactions in the lithium aluminum hydride reduction of formaldehyde, and 12. π molecular orbitals in 1,3-butadiene. The prints are made with hobby-grade 5-color 3D fused deposition modeling (FDM) printers and sized to provide compact take-home class handouts for each student or projected in-class with a document camera. Models are fabricated with orbital or electron density surface bisections and text annotations to enhance information content. Student perceptions of this set of 3D-printed molecular models are generally favorable and have improved their understanding of course materials.