Multicolor 3D-Printed\nMolecular Orbital Models for\na First-Semester Organic Chemistry Course

We have developed a set of multicolor 3D-printed structural\nand\nmolecular orbital models for use in a first-semester organic chemistry\ncourse. These models provide visual and tactile insights regarding\naspects of organic structure, reactivity, and mechanistic “arrow\npushing”. The set includes: 1. orbital models of σ and\nπ bonding in methane and ethylene, 2. σ<sub>CH</sub>–σ*<sub>CH</sub> hyperconjugation in staggered and eclipsed ethane conformations,\n3. LUMO accessibility in S<sub>N</sub>2 electrophiles and HOMO–LUMO\norbital interactions in S<sub>N</sub>2 transition states, 4. E2 transition\nstate structure and orbital interactions in β-hydrogen removal\nand π bond formation, 5. σ<sub>CH</sub>–<i>p</i><sub>C</sub> hyperconjugation in the ethyl cation, 6. transition\nstate structure and σ<sub>CH</sub>–<i>p</i><sub>C</sub> orbital interactions in a carbocation 1,2-hydride shift,\n7. late and early, respectively, Br• and Cl• H atom\nradical abstraction transition state structures and SOMO orbitals,\n8. bromonium ion structure and LUMO orbital, 9. protonated epoxide\nion and neutral epoxide structures and LUMO orbitals, 10. transition\nstate structure and orbital interactions in a hydroboration reaction,\n11. transition state structure and orbital interactions in the lithium\naluminum hydride reduction of formaldehyde, and 12. π molecular\norbitals in 1,3-butadiene. The prints are made with hobby-grade 5-color\n3D fused deposition modeling (FDM) printers and sized to provide compact\ntake-home class handouts for each student or projected in-class with\na document camera. Models are fabricated with orbital or electron\ndensity surface bisections and text annotations to enhance information\ncontent. Student perceptions of this set of 3D-printed molecular models\nare generally favorable and have improved their understanding of course\nmaterials.