Draw a porphine core

Implementation notes and historical checks. Open the visual guide →.

The porphine template places a free-base 21H,23H-porphine core with equal bond lengths and both N–H labels pointing inward. You can also build the scaffold yourself with the reference align/stretch controls.

Use it

Place the template

1. Open Templates → Macrocycles → Porphine (21H,23H), or search for porphyrin.
2. Place it in empty space. The core uses the drawing’s bond length and stays editable.

The outline has four regular five-membered rings, equal bond lengths and 120° meso corners. Its two opposite N–H labels point inward, and they stay inward after Flip vertical, Flip horizontal or a 90° rotation.

Build the scaffold yourself

1. Start with one regular carbon five-ring and one meso arm.
2. Use Reference: align / stretch to set the arm to 14.4 pt along its own axis, then align the outer ring edge horizontally. Pin the common point.
3. Copy the original at 90°, 180° and 270° around that point with Copy + rotate.
4. Add the four links from each meso site to the next ring. This is still a carbon scaffold.
5. Assign the four inward nitrogens and the bond pattern. Set only opposite nitrogens to N–H, and check that the formula is C20H14N4.

Add a meso substituent

1. Choose the Benzene template and its source atom with Connect with a bond, then attach it at an outward meso carbon.
2. Use Stretch bond to change only the bridge length. The macrocycle and the phenyl ring stay rigid. The result is C26H18N4.

Limits

• The template is the free base only. Metal complexes and substituted porphyrins need their own checks.
• Ring bonds cannot be stretched alone.
• Building the scaffold by hand is a set of construction stages, not a measured number of clicks.

Implementation notes

This is explicitly 21H,23H-porphine, C20H14N4, with opposite N–H sites. The graph agrees with official OPSIN’s name parsing and the original ChemIDplus depositor record. The graph without specified macrocyclic double-bond geometry has InChIKey RKCAIXNGYQCCAL-UHFFFAOYSA-N; the chosen planar depiction has RKCAIXNGYQCCAL-CEVVSZFKSA-N. These are separate facts in the catalog. The standardized PubChem CID 66868 represents another N–H placement and is not the exact-tautomer reference for this drawing. Fourfold outline symmetry does not make the N–H tautomer fourfold chemically symmetric.

Coordinates come from a regular-pentagon construction and exact quarter turns. For bond length L, the five-ring radius is L / (2 sin 36°); the common-center distance is R sin 72° + R cos 72° + sqrt(1.5) L. At the default size the ring center is 96.45835 drawing units from the common center. No reference-editor artwork or coordinates are bundled. The regeneration script validates the catalog’s chemical graph and keeps this model-generated layout.

Fixed hydrogen positions (Left, Right, Above, Below) follow flips and rotations of the selected atoms: each takes the nearest side after the transform, and an exact 45° diagonal picks Left or Right. Automatic stays automatic, and label text stays upright.

Scaffold fixtures

The user’s twelve-stage guide uses temporary helper polygons and guide lines to keep symmetry and bond lengths. The construction fixtures instead demonstrate five scaffold stages. The supplied seed has a 17.3° reference edge and a 21.6 pt arm, so it exercises arbitrary angles, and the common point is pinned at X=0, Y=0. The supplied fixtures demonstrate the algorithm through the application’s geometry and renderer. The desktop record also covers successive 90° copies, closure and N/bond assignment from that supplied seed; from-blank step counts and timing comparisons were not measured. The template is the direct placement route.

Reproduce the figures

cargo run --locked --example porphine_core_qa -- /tmp/porphine-core

The generator writes editable .rsk files, actual SVG/PNG/PDF output, the chosen template and constructed-core identity reports, seven scaffold/substitution stages, and exact reproduction notes. Each image must be inspected before publication. The desktop record covers template search and placement, shared-pivot copies, bridge stretching and fresh reopening, with editable input/save files and independent chemistry checks.