The term tautomerism (from raviathe same -and #fpOC; -part -was coined by Laar [3] in 1885. Laar interpreted tautomerism not as dynamic isomerism but as a possibility that one substance may combine properties of two or more isomers resulting from the fact that one of the groups, usually hydrogen, occupies an intermediate location between two or more possible positions. The development ofthe term tautomerism has been traced in [4,5].