Comproportionation or synproportionation is a chemical reaction where two reactants, each containing the same element but with a different oxidation number, will form a product in which the elements involved reach the same oxidation number. For example, an element A in the oxidation states 0 and +2 can comproportionate to the state +1. It is opposite to disproportionation, where two or more atoms of the same element originally having the same oxidation state react with other chemical(s) or themselves to give different oxidation numbers.
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Frost diagrams
The tendency of two species to disproportionate can be determined by examining the Frost diagram of the oxidation states; if a species' value of ΔG/F is lower than the line joining the two oxidation numbers on either side of it, then it is more stable and if in a solution, these two species will undergo comproportionation.