Five different hydrogen-bonded conformers of the dimer of 2-propanol have been characterized by Fourier transform microwave spectroscopy. In all observed species, the proton donor moiety adopts a gauche conformation. While in the gauche monomer a transient chirality takes place, all dimers are classical chiral systems. The Ubbelohde effect has been observed upon OH -> OD isotopic substitution and its structural effects a 5 mA reduction of the O-O distance have been quantitatively defined.