A
selectively labelled compound may be multiply
labelled when in the unmodified compound there is more than one atom
of the same element at the position where the isotopic modification
occurs, e.g.
H
in
CH4, or there are several atoms of the same
element at different positions where the isotopic modification
occurs, e.g.
C in
C4H8O.
Source:
PAC, 1981, 53, 1887
(Nomenclature of inorganic chemistry: II.1 - Isotopically modified compounds)
on page 1893