Title: indicated hydrogen
Long Title: IUPAC Gold Book - indicated hydrogen
DOI: 10.1351/goldbook.I03004
Status: current

Definition
Under certain circumstances it is necessary to indicate in the name of a ring, or ring system, containing the maximum number of non-cumulative double bonds, one or more positions where no multiple bond is attached. This is done by specifying the presence of an 'extra' hydrogen atom at such positions by citation of the appropriate numbered locant followed by an italicized capital H.Example:  A second type of indicated hydrogen (sometimes referred to as 'added hydrogen') describes hydrogen atoms added to a specific structure as a consequence of the addition of a suffix or a prefix describing a structural modification. This type of indicated hydrogen is normally cited in parentheses after the locant of the additional feature.Example: 

Related Term
- cumulative double bonds: https://goldbook.iupac.org/terms/view/C01437

Source
- Blue Book Guide, p. 34 (https://doi.org/10.1351/pac199971071327)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/I03004/html
- json: https://goldbook.iupac.org/terms/view/I03004/json
- xml: https://goldbook.iupac.org/terms/view/I03004/xml

Citation: Citation: 'indicated hydrogen' 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.I03004
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Accessed: 2026-06-28T09:34:37+00:00