chematic-inchi

InChI and InChIKey generation for Rust. Two modes:

Standard IUPAC InChI (native-inchi feature)

Enable the native-inchi feature to link the vendored IUPAC InChI C library (v1.07.5, MIT). Output is bit-exact with the reference implementation.

[dependencies]
chematic-inchi = { version = "0.4", features = ["native-inchi"] }

use chematic_inchi::{standard_inchi, standard_inchi_key};
use chematic_smiles::parse;

let mol = parse("c1ccccc1").expect("benzene");
let inchi_str = standard_inchi(&mol).unwrap();
// Produces the IUPAC-standard InChI (canonical order matches reference):
// InChI=1S/C6H6/c1-2-4-6-5-3-1/h1-6H
let key = standard_inchi_key(&inchi_str).unwrap();
assert_eq!(key, "UHOVQNZJYSORNB-UHFFFAOYSA-N");

All layers are handled by the IUPAC reference library: formula, connectivity, hydrogen, tautomer normalization, mobile-H, stereo (/b E/Z double-bond, /t tetrahedral, /m, /s), charge (/q, /p), and isotope (/i).

Known limitation: 2 of 5,000 drug-like molecules (0.04%) still fail with InchiError::KekulizationFailed: one boron-aromatic ring (b1ccccn1) and pure H₂ ([H][H], which has no heavy atoms). All other previously failing molecules — including indolizine-type bridgehead-N systems (~109 cases) and complex polycyclics (~17 cases) — are now handled by the 4-pass kekulization algorithm in chematic-core. No silent wrong output is produced; the error is always explicit.

Approximate InChI (WASM / zero-C-dependency fallback)

The default inchi() / inchi_key() functions are not standard IUPAC InChI. They use a different canonical ordering and do not implement tautomer or mobile-H normalization. Use them only when WASM compatibility or a zero-C-dependency build is required.

use chematic_inchi::inchi;
use chematic_smiles::parse;

let mol = parse("c1ccccc1").expect("benzene");
// Non-standard approximation — does NOT match the IUPAC reference:
let approx = inchi(&mol);

Dependencies

• chematic-core — molecular graph types
• chematic-smiles — SMILES parser
• chematic-chem — CIP rules for stereo assignment
• sha2 — SHA-256 for approximate InChIKey hash
• cc (optional, native-inchi only) — C compiler for vendored IUPAC library

References

• IUPAC InChI standard: https://iupac.org/what-we-do/inchi/
• InChI Trust: https://www.inchi-trust.org/

See Also

• chematic — main umbrella crate
• chematic-smiles — SMILES I/O
• chematic-depict — SVG 2D structure drawing