Square brackets isotopic labeling

Rules for designating isotopic substitution and labelling are given in [13] (Section H). Parentheses indicate substitution square brackets indicate labelling. The locant U indicates uniform labelling. 

An isotopically labeled compound is a mixture of an isotopically unmodified compound with an analogous isotopically substituted compound or compounds. Isotopically labeled compounds may be specifically labeled or selectively labeled. To indicate isotopic labeling, the number and symbol (and locants if needed) are enclosed in square brackets closed up to the compound name or formula. 

When it is unknown or irrelevant whether the compound is isotopically labeled or isotopically substituted, simply hyphenate the isotope symbol to the compound name and do not use square brackets or parentheses. 

There are two main methods used for naming isotopically labelled compounds. For specifically labelled compounds, lUPAC recommends forming the name by placing the nuclide symbols (plus locants if necessary) in square brackets before the name of the unlabelled compounds or that part of the name which is isotopically modified. 

IR-4.5.3.2 Specifically labelled compounds An isotopically labelled compound is called a specifically labelled compound when a unique isotopically substituted compound is added formally to the analogous isotopically unmodified compound. A specifically labelled compound is indicated by enclosing the appropriate nuclide symbol(s) and multiplying subscript (if any) in square brackets. 

Species are listed in alphabetical order. The position of isotopes in the precursors fed and in the labelled alkaloids formed are indicated with a heavy dot or an asterisk. Incorporations are reported either as Absolute incorpora-tions (the total radioactivity found in the isolated alkaloid divided by the total radioactivity fed to the plant) or Specific incorporations (the specific activity of the isolated alkaloid divided by the spiecific activity of the administered Compound). Specific incorporations are recorded in square brackets [ ]. 

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