Ketoses are the isomers of aldoses except that, with very few exceptions, the keto group appears at position 2. As a result, there is one less asymmetric center than in an aldose with the same number of carbons.
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| D-glycerotetrulose | |||
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| D-erythropentulose | D-threopentulose | ||
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| D-psicose | D-fructose | D-sorbose | D-tagatose |