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:
Source:
InChI=1/C4H5N/c1-2-4-5-3-1/h1,3-4H,2H2
InChI=1/C5H5P/c1-2-4-6-5-3-1/h1-5H
InChI=1/C5H5OP/c6-5-3-1-2-4-7-5/h1-4,7H
VXIKDBJPBRMXBP-UHFFFAOYAS
UNQNIRQQBJCMQR-UHFFFAOYAZ
ZULCYBOYDXQMTM-UHFFFAOYAP
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.
