{"term":{"id":"00415","title":"apical","longtitle":"IUPAC Gold Book - apical","doi":"10.1351\/goldbook.A00415","code":"A00415","status":"current","definitions":[{"id":1,"text":"In trigonal bipyramidal structures (e.g. a five-coordinate trigonal bipyramid with phosphorus as central atom) the term apical refers to the two positions that are collinear with the central atom or to the bonds linking these positions to the central atom. The three equivalent bonds (or positions) in a plane passing through the central atom and perpendicular to the direction of the apical bonds are described as equatorial.  The term apical is also used for the bond pointing from the atom at or near the centre of the base to the apex of a pyramidal structure. The positions at or near the base of the pyramid, or the bonds linking those positions to the central atom of the base are described as 'basal'. The apical bonds have also been called axial. ","links":[{"term":"axial, equatorial","url":"https:\/\/goldbook.iupac.org\/terms\/view\/A00546"},{"term":"central atom","url":"https:\/\/goldbook.iupac.org\/terms\/view\/C00930"},{"term":"equatorial","url":"https:\/\/goldbook.iupac.org\/terms\/view\/E02174"}],"sources":["PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2199 (https:\/\/doi.org\/10.1351\/pac199668122193)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/A00415\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/A00415\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/A00415\/plain"},"citation":"Citation: 'apical' 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.A00415","license":"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.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"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.","accessed":"2026-06-30T08:29:03+00:00"}}