As summarized by Jones (Chem. Rev. 1963, 461) in his summary on "Ring-chain tautomerism", potentially interacting funtional groups held spatially in near proximity can interact to generate intramolecular cyclic structures. Ortho aromatic substituents fulfill these requirements. Interaction between a carboxylic acid group and an aldehyde or ketone can produce a cyclic lactol or pseudoacid (often called a phthalide in the ortho-aromatic cases). These may be thought of as a cyclization like that which occurs in sugars (hydroxy aldehydes and ketones) with each of the functions in the next highest carbon oxidation state.
An example is o-carboxyphenylacetaldehyde, as prepared by Schopf & Kuhne (Chem. Ber. 1950, 83:390) by oxidation of 2-hydroxy-1-indanone. The compound can cyclize to form the 6-ring pseudoacid.
The structure ( picture or .pdb ) is found in the cyclic for in
the solid state, and in solution in non-polar
solvents, it is also in the cyclic form.
Among the 5-ring possibilities, two common examples can be cited.
The compounds o-formylbenzoic acid and
o-acetylbenzoic acid are found in the cyclic forms in the solid and in
solution in non-polar
solvents. 
The crystal structures of both of these can be viewed.
Pseudoacids
from the aldehyde (
picture or .pdb )
from the ketone ( picture or .pdb )
Our interests have also developed toward the
derivatives of pseudoacids .
Constructed by Edward J. Valente, contact valente@mc.edu.
