Chemical nomenclature — IUPAC systematic naming conventions and the associated formal-language / combinatorial machinery that makes the system unambiguous. Foundations: (1) Substitutive nomenclature (IUPAC Blue Book 2013) — identify the…
chemical-nomenclature
IUPAC substitutive nomenclature: parent-chain + locants + suffix-priority
Substitutive IUPAC nomenclature (Blue Book, Favre & Powell 2013) is the canonical algorithmic procedure for naming organic compounds. Step…
CIP (Cahn-Ingold-Prelog) priority: R/S from S₄-permutation parity
Cahn-Ingold-Prelog stereodescriptors (Cahn, Ingold, Prelog 1956 / 1966). For a tetrahedral stereocenter with four distinct substituents,…
Oxidation-state assignment: EN-based bond partition; Σ OS = molecular charge
Oxidation-state assignment rules (IUPAC recommendations 2016, Karen et al.). For each atom A in the Lewis structure: (i) list its valence…
Locant-min: heptane C-3,C-4 substituents ⇒ (3,4) < (4,5) lex-min
Sympy-exact witness of the IUPAC lowest-locant rule on a heptane (n = 7) parent chain bearing two substituents at positions 3 and 4. …
CIP parity: cyclic σ=(0 1 2) sgn=+1 (S); transposition sgn=−1 (R)
Sympy-exact witness of the CIP priority-permutation parity identity using sympy.combinatorics. Permutation. The 3-cycle (0 1 2) acting on…
OS balance: KMnO₄ ⇒ Mn = +7; Cr₂O₇²⁻ ⇒ Cr = +6; Σ OS = q_mol
Sympy-exact witness of the oxidation-state conservation identity on two textbook anchors. KMnO₄ (potassium permanganate, neutral): K at…
IUPAC lowest-locant tiebreak framework: first-point-of-difference rule for locant-set comparison (P-14.5.2)
The IUPAC lowest-locant tiebreak rule (Recommendations P-14.5.2): when two candidate numbering schemes produce locant sets of equal…
CIP stereodescriptor swap-parity framework: (−1)^N signature under transposition of ranked substituents
Cahn-Ingold-Prelog stereodescriptor parity under transposition: the R/S descriptor at a stereocentre is invariant under any even…
Hantzsch-Widman heteroatom-replacement framework: standard prefix table (oxa/thia/aza) for monocyclic heterocycles
The Hantzsch-Widman 1887 heteroatom-replacement nomenclature: for monocyclic rings a standard table assigns prefixes to the most common…
IUPAC locant tiebreak: {1,2,4} < {1,3,5} at first point of difference (2 < 3 at position 1)
At first point of difference, {1,2,4} < {1,3,5} because 2 < 3 at position 1. Canonical pins: locant-sums 7 and 9 (exact integers);…
CIP swap parity: (−1)^N = 1 at N=2 (even preserves R/S); (−1)^N = −1 at N=3 (odd inverts)
(−1)^N takes value +1 for N = 2 (even swaps preserve R/S) and −1 for N = 3 (odd swaps invert R↔S). Canonical pins: parity symbol (−1)^N;…
Hantzsch-Widman replacement: oxa = Z(O) = 8; thia = Z(S) = 16; aza = Z(N) = 7 (periodic-table classifier)
Hantzsch-Widman prefix-to-atomic-number classifier: oxa → Z=8 (oxygen), thia → Z=16 (sulfur), aza → Z=7 (nitrogen). Canonical pins: three…
IUPAC 2013 recommendations
IUPAC 2013 nomenclature of organic chemistry: longest carbon-chain root + suffix functional-group + numbered substituents alphabetical;…
CAS Registry Number system
Chemical Abstracts Service 1965 unique-identifier registry; XXXXXXX-XX-X format; 200M+ substances by 2024; check-digit modulo-10…
InChI standard identifier (2005)
IUPAC InChI 2005 standard hashed + non-proprietary chemical-structure descriptor; layer-based skeletal/H/charge/stereo; InChIKey 27-char…
SMILES notation (Weininger 1988)
Daylight Chemical 1988 SMILES: linear ASCII molecular structure; canonical algorithm gives unique string; basis of cheminformatics + ML…
CIP rules (Cahn-Ingold-Prelog 1956)
Cahn-Ingold-Prelog 1956 priority rules for stereo: atomic number, then mass-number, then phantom-atom rule; assigns R/S at chiral centers +…
Hill system (1900)
E A Hill 1900 molecular-formula ordering: C first, H second, then alphabetical; standard for journals + databases (CAS); for non-C…
IUPAC 2013 nomenclature
IUPAC 2013 'Nomenclature of Organic Chemistry' P-recommendations; modern preferred-IUPAC-name PIN + retained-trivial usage rules.
CAS registry (1965)
Chemical Abstracts Service 1965 CAS-RN; modern 200M+ unique substance registry + identifier + CAS-Search + commercial-IP standard.
InChI (Stein 2003)
S Stein 2003 + Heller 2015 IUPAC-International-Chemical-Identifier; modern open-source canonical hash + InChIKey database lookup.
SMILES (Weininger 1988)
D Weininger 1988 SMILES line-notation; modern canonical-SMILES + SMARTS-pattern + RDKit / OpenBabel parsing standard.
CIP rules (Cahn-Ingold-Prelog 1956)
Cahn-Ingold-Prelog 1956 R/S stereodescriptor priority-rules; modern E/Z double-bond + axial-chirality M/P helicene assignment.
Isotope notation (Aston 1923)
F Aston 1923 (Nobel 1922) mass-spectrograph isotope-notation; modern atomic-mass-evaluation AME 2020 5σ-precision standards.