Molecular Properties & Oxidation

Chlorine dioxide is a small, volatile, and very strong molecule that reacts with other substances by way of oxidation rather
than by substitution (i.e., chlorination). Chlorine dioxide has lower oxidation strength than chlorine, but more than twice the oxidative capacity.
Oxidation strength describes how strongly an oxidizer will react with an "oxidizable" substance. The higher its oxidation strength,
the more substances the oxidant compound will react with. Chlorine dioxide is comparatively weak, and has a lower oxidation potential than ozone,
chlorine or even hypochlorous acid. Oxidation capacity refers to the number of electrons transferred during an oxidation or reduction reaction.
The chlorine atom in the ClO₂ molecule has an oxidation number of +4. For this reason ClO₂ accepts 5 electrons when reduced to chloride ion.
By way of comparison, ClO₂ contains 263 percent 'available chlorine', which is more than 2.5 times the oxidation capacity of chlorine.

 
Because chlorine dioxide has lower oxidation strength, it is more selective in its reactions. Typically, chlorine dioxide will only react with compounds that have activated carbon bonds such as phenols, or with other active compounds like sulfides, cyanides, and reduced iron and manganese compounds.
Chlorine is a more powerful oxidizer than chlorine dioxide, and will react with a wider variety of chemicals, including ammonia. 
This property limits its overall effectiveness as a biocide. Conversely, because chlorine dioxide has more oxidative capacity compared to ozone or chlorine, 
less chlorine dioxide is required to obtain an active residual concentration of the material when used as a disinfectant.

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