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:
