This entry presents Phenylacetic Acid (C8H8O2; CAS 103-82-2; PubChem CID 999) as a 3D-printable ball-and-stick model in which every atom carries its engraved element symbol (C, H, O), so the model can be read without a colour key. Atomic coordinates come from the PubChem-computed 3D conformer (not an experimental crystal structure); coordinates and connectivity are unchanged.

Project scope and purpose

MolGod is an open educational-science project that publishes engraved ball-and-stick models of individual chemical compounds. Models are generated deterministically from public structure data and released under CC BY-SA 4.0 together with their identifiers and provenance.

Standard molecular STL files encode geometry only; atom identity, conventionally conveyed by colour, is lost in single-material additive manufacturing. In these models the element symbol is a recessed engraving on each atomic sphere, so atom identity is part of the mesh and remains readable in any print material, visually and by touch.

The design objective is to shorten the time learners need to identify the atoms of a molecule, so that instruction can concentrate on connectivity, bond order and three-dimensional geometry, and to reduce teacher preparation to scaling and slicing a ready file. This is a design rationale: the effect on learning outcomes has not yet been formally evaluated.

Project rationale, related peer-reviewed research and the validation plan: molgod.org/engraved-molecular-models.

Structure at a glance

• 18 atoms: 8 C, 8 H, 2 O

• 18 bonds: 11 single, 1 double, 6 aromatic

• One aromatic 6-membered ring

• Functional group: one carboxylic acid group (-COOH)

• Fraction of sp3-hybridised (tetrahedral) carbon atoms: 0.12 (computed)

Use in teaching

• Counting task: students tally the engraved symbols (8 C, 8 H, 2 O; 18 atoms) and rebuild the formula C8H8O2 from the model alone.

• Aromaticity: identify the aromatic ring and the 6 bonds recorded as aromatic; the model draws them as one Kekulé structure (alternating single and double bonds), while in the real molecule they are delocalised, intermediate between single and double.

• Functional groups: find the carboxylic acid group (-COOH) on the model and name it.

File and printing

STL mesh of 233,364 triangles, a closed (watertight) single solid. Coordinates are in ångström and STL stores no unit, so scale the model deliberately in your slicer. Measured bounding box: 6.574 × 6.152 × 4.718 Å; at scale factor 10 (1 Å to 10 mm, file read in millimetres) the print measures about 65.7 × 61.5 × 47.2 mm. SHA-256: d8f0eef357ced2a60ff7df6c1ef094110456b426b39095dec22a2e06c017ad43.

Validation

• InChIKey identical to the PubChem record (PubChem FTP SDF, file dated 2026-10-08): WLJVXDMOQOGPHL-UHFFFAOYSA-N

• Molecular formula identical to PubChem

• Mesh: triangle count in the header equals the actual count; 0 edges not shared by exactly two triangles; 1 connected solid; SHA-256 equal to the published file

Source, licence and identifiers

Full record: molgod.org/molecule/103-82-2 · Licence and provenance record: molgod.org/licenses/stl/103-82-2 · Same file on Wikimedia Commons: File:Phenylacetic Acid-3D-molecular-model-engraved-CAS-103-82-2.stl

• MolGod ID: MG_517-022-974-73

• Wikidata: Q410842

• EC number: 203-148-6

• ChemSpider ID: 10181341

• IUPAC name: 2-phenylacetic acid

• InChIKey: WLJVXDMOQOGPHL-UHFFFAOYSA-N

• SMILES: C1=CC=C(C=C1)CC(=O)O

• Molar mass 136.15 g/mol (exact mass 136.052429494)

Licence: CC BY-SA 4.0 (licence text). Required attribution: "Phenylacetic Acid 3D model by MolGod.org — https://molgod.org/molecule/103-82-2/ — CC BY-SA 4.0".