(+/-)-1-indanone-2-acetic and -2-propionic acids: catemeric versus dimerichydrogen bonding in homologous gamma- and delta-keto acids

The crystal structure of (+/-)-2,3-dihydro-1-oxo-1H-indene-2-acetic acid (C 11H10O3) involves catemeric hydrogen bonds, which progress from the carboxy l H atom of one molecule to the ketone O atom of a neighbor screw-related i n b [O ... O = 2.709(2) Angstrom]. This yields centrosymmetrically related counterdirectional pairs of hydrogen-bonding chains following parallel heli cal axes. Four intermolecular C=O ... H-C close contacts were found, involv ing both carbonyl groups. By contrast, the hydrogen bonding in (+/-)-3-(2,3 -dihydro-1-oxo-1H-inden-2-yl)propionic acid (C12H12O3) produces carboxyl di mers [O ... O = 2.639 (2) Angstrom], which also have a 2.62 Angstrom C=O .. . H-C close contact involving the ketone carbonyl group and the peri-hydrog en on a centrosymmetrically related molecule. The difference in hydrogen-bo nding behavior between the two molecules is discussed.