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A raised mass number before an element symbol in a formula.
Also known as: Isotopic labelling, Isotope label, Raised number before an element, Tracer notation
A superscript mass number written into a formula marks a deliberately enriched isotope, used to trace where an atom ends up. It is how the mechanism of most reactions was actually established: label one oxygen and see which product it appears in.
Denotes deliberate isotopic enrichment at a specified position, written as a raised mass number before the element symbol.
Contexts: Laboratory
Is the basis of mechanistic labelling experiments, which establish reaction pathways by following a marked atom into the products.
Contexts: Laboratory
Is distinguished from the general nuclide notation by appearing inside a structural or molecular formula rather than standing alone.
Contexts: Laboratory
A small numeral raised to the upper left of an element's letter symbol within a longer formula.