Pseudoacid

A Pseudoacid in Organic Chemistry is a cyclic oxocarboxylic acid. Most commonly, these form from aldehyde and keto carboxylic acids, and the cyclic forms are furanoid (5-ring with oxygen) or pyranoid (6-ring with oxygen). The original pseudoacid to be described as such (using the German "pseudosauren") was levulinic acid (4-oxopentanoic acid).