The unpaired @E01986@ at a position of interest, usually at carbon, in a @R05066@. It is often measured experimentally by electron @P04404@ @R05326@ [EPR, ESR (electron spin @R05326@)] @S05848@ through @HT07052@ constants of the atom or an attached hydrogen.
See also:
radical centre
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1166 [Terms] [Paper]