04677 IUPAC Gold Book - pitch 10.1351/goldbook.P04677 P04677 current 1 A residue from pyrolysis of organic material or tar distillation which is solid at room temperature, consisting of a complex mixture of numerous, essentially aromatic hydrocarbons and heterocyclic compounds. It exhibits a broad softening range instead of a defined melting temperature. When cooled from the melt, pitches solidify without crystallization. The ratio of aromatic to aliphatic hydrogen depends mainly on the source of the starting material. The hydrogen aromaticity (ratio of aromatic to total hydrogen atoms) varies between 0.3 and 0.9. The aliphatic hydrogen in pitch is largely associated with alkyl side chains substituted on aromatic rings. The content of heterocyclic compounds in pitches varies depending on their origins. Also, the softening temperature can vary in a broad range between about \(320\) and \(570\ \rm{K}\) depending on the molecular weight (relative molecular mass) and composition of the constituents. aromaticity https://goldbook.iupac.org//terms/view/A00442 crystallization https://goldbook.iupac.org//terms/view/C01434 heterocyclic compounds https://goldbook.iupac.org//terms/view/H02798 hydrocarbons https://goldbook.iupac.org//terms/view/H02889 melting https://goldbook.iupac.org//terms/view/M03821 molecular weight https://goldbook.iupac.org//terms/view/M04000 pyrolysis https://goldbook.iupac.org//terms/view/P04961 relative molecular mass https://goldbook.iupac.org//terms/view/R05271 PAC, 1995, 67, 473. 'Recommended terminology for the description of carbon as a solid (IUPAC Recommendations 1995)' on page 500 (https://doi.org/10.1351/pac199567030473) https://goldbook.iupac.org/terms/view/P04677/html https://goldbook.iupac.org/terms/view/P04677/json https://goldbook.iupac.org/terms/view/P04677/plain Citation: 'pitch' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.P04677 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-04-19T02:24:03+00:00