Hydrogen polyoxide
Hydrogen polyoxides (also known as oxidanes, oxohydrogens, or oxyhydrogens) are chemical compounds that consist only of hydrogen and oxygen atoms, are bonded exclusively by single bonds (i.e., they are saturated), and are acyclic (have molecular structures containing no cycles or loops). They can, therefore, be classed as hydrogen chalcogenides. The simplest possible stable hydrogen polyoxide (the parent molecule) is water, HO. The general structure of the class of molecules is some number of oxygen atoms single-bonded to each other in a chain. The oxygen atom at each end of this oxygen skeleton is attached to a hydrogen  atom. Thus, these compounds form a homologous series with chemical formula in which the members differ by a constant relative molecular mass of 16 (the mass of each additional oxygen atom). The number of oxygen atoms is used to define the size of the hydrogen polyoxide (e.g., hydrogen pentoxide contains a five-oxygen backbone). An oxidanyl group is a functional group or side-chain analog of hydrogen polyoxide that is attached to some structure other than just a hydrogen atom. Examples include the hydroxy (oxidyl) and hydroperoxy (dioxidanyl) groups. Specific examples. HO. Several molecules are known where one end of  the polyoxide chain is protonated and the other is an unprotonated radical: HO. Neutral dihydrogen polyoxides containing up to five oxygen atoms have been produced experimentally. Hydrogen polyoxides containing up to 10 oxygen atoms have been studied theoretically, but those containing more than five oxygens are expected to be extremely unstable. Ionization. All the hydrogen polyoxides are known or expected to autoionise when in liquid form, with the acidic hydrogen being solvated by other of the neutral polyoxide molecules. Specific ions include: