molecular entity
any constitutionally or isotopically distinct atom, molecule, ion, ion pair, radical, radical ion, complex, conformer, etc., identifiable as a separately distinguishable entity
molecule
smallest possibile amount of a chemical substance
parent compound
organic compound in which no additional substituents or functionalities are present
structural analog
compound having a structure similar to that of another compound, but differing from it in respect to a certain component
complex
any molecular association based on other forces than covalent liaisons
radical
atom, molecule, or ion that has an unpaired valence electron; typically highly reactive
divalent
element, ion, functional group, or molecule has a valence of two
reaction intermediate
molecular entity that is formed from the reactants (or preceding intermediates) and reacts further to give the directly observed products of a chemical reaction
complex
molecular entity formed by loose association involving two or more component molecular entities (ionic or uncharged), or the corresponding chemical species
functional group
group of atoms in a molecule which imparts specific chemical properties
ion
atom or molecule in which the total number of electrons is not equal to the total number of protons, giving the atom a net positive or negative electrical charge
Lewis base
molecular entity that can donate electrons to a Lewis acid to form a covalent bond