Conformation of chiral molecules: The rotational spectrum of 2-chloropropionic acid

Reported here are measurements of the rotational spectra of two isotopologues (35Cl and 37Cl) of one of the simplest chiral carboxylic acids, 2-chloropropionic acid. The spectra have been obtained in a supersonic expansion, using free-jet millimeter-wave direct-absorption as well as pulsed-jet FT microwave spectroscopies. A single conformer has been detected, characterized by a methyl group nearly cis with respect to the carbonylic oxygen. Within the realm of chiral recognition, the relative simplicity of the observed spectrum should allow for the detection of the microwave spectrum of the polar homo-dimer.