Characteristics of tautomerism
(a) Tautomerism (cationotropy) is caused by the oscillation of hydrogen atom between two polyvalent atoms present in the molecule. The modification is accompanied by the essential rearrangement of single and double bonds.
(b) It is a reversible intramolecular modification.
(c) The tautomeric forms remain in dynamic equilibrium. Hence, their replacement is a bit hard. Although their separation may be done by special procedures, yet they form a separate sequence of stable derivatives.
(d) The two tautomeric forms differ in their stability. The less stable form is known as the labile form. The relative proportion of two types varies from substance to substance and also with temperature, solvent etc. The modification of one form into another is also catalysed by acids and bases.
(e) Tautomers are in dynamic equilibrium with each other and interconvertible (?).
(f) Two tautomers have different functional sets.
(g) Tautomerism has no effect on covalent bond length.
(h) Tautomerism has no contribution in stabilising the molecule and does not lower its energy.