Preferred Label : chemical species;
IUPAC definition : An ensemble of chemically identical molecular entities that can explore the same set
of molecular energy levels on the time scale of the experiment. The term is applied
equally to a set of chemically identical atomic or molecular structural units in a
solid array. For example, two conformational isomers may be interconverted sufficiently
slowly to be detectable by separate NMR spectra and hence to be considered to be separate
chemical species on a time scale governed by the radiofrequency of the spectrometer
used. On the other hand, in a slow chemical reaction the same mixture of conformers
may behave as a single chemical species, i.e. there is virtually complete equilibrium
population of the total set of molecular energy levels belonging to the two conformers.
Except where the context requires otherwise, the term is taken to refer to a set of
molecular entities containing isotopes in their natural abundance. The wording of
the definition given in the first paragraph is intended to embrace both cases such
as graphite, sodium chloride or a surface oxide, where the basic structural units
may not be capable of isolated existence, as well as those cases where they are. In
common chemical usage generic and specific chemical names (such as radical or hydroxide
ion) or chemical formulae refer either to a chemical species or to a molecular entity.;
Origin ID : CT01038;
See also
An ensemble of chemically identical molecular entities that can explore the same set
of molecular energy levels on the time scale of the experiment. The term is applied
equally to a set of chemically identical atomic or molecular structural units in a
solid array. For example, two conformational isomers may be interconverted sufficiently
slowly to be detectable by separate NMR spectra and hence to be considered to be separate
chemical species on a time scale governed by the radiofrequency of the spectrometer
used. On the other hand, in a slow chemical reaction the same mixture of conformers
may behave as a single chemical species, i.e. there is virtually complete equilibrium
population of the total set of molecular energy levels belonging to the two conformers.
Except where the context requires otherwise, the term is taken to refer to a set of
molecular entities containing isotopes in their natural abundance. The wording of
the definition given in the first paragraph is intended to embrace both cases such
as graphite, sodium chloride or a surface oxide, where the basic structural units
may not be capable of isolated existence, as well as those cases where they are. In
common chemical usage generic and specific chemical names (such as radical or hydroxide
ion) or chemical formulae refer either to a chemical species or to a molecular entity.
