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Spiro compound

A spiro compound is a bicyclic organic compound with rings connected through just one atom. The rings can be different in nature or identical. the connecting atom is also called the spiroatom, most often a quaternary carbon ("spiro carbon"). All spiro compounds have the infix spiro followed by square brackets [] containing the number of atoms in the smaller ring and the number of atoms in the larger ring excluding the spiroatom itself. For example compound A is called 1-bromo-3-chlorospiro[4.5]decan-7-ol and compound B is called 1-bromo-3-chlorospiro[3.6]decan-7-ol. The spiro compound consisting of a cyclohexane ring and a cyclopentane ring is called spiro[4.5]decane. This nomenclature was proposed by Adolf von Baeyer in 1900 ^[1].

Some spiro compounds exhibit axial chirality. Spiroatoms can be centers of chirality even when they lack the required four different substituents normally observed in chirality. When two rings are identical the priority is determined by a slight modification of the CIP system assigning a higher priority to one ring extension and a lower priority to an extension in the other ring. When rings are dissimilar the regular rules apply.