HYDROGEN-BONDS TO CARBOXYLATE GROUPS - SYN/ANTI DISTRIBUTIONS AND STERIC EFFECTS

The syn/anti distribution for hydrogen bonds to small-molecule carboxylate groups has been analyzed. The data set used consisted of 15 acetate structures, 48 primary carboxylates, 172 secondary carboxylates, and 20 ternary carboxylates retrieved from the Cambridge Structural Database. For 876 interactions there is overall a slight preference for syn geometry with a clear correlation between the syn/anti ratio and steric hindrance in the anti positions between the donor and substituents on the acceptor molecule. In the absence of steric interference, syn H-bonds are not significantly preferred according to statistics. It is shown that the stereoelectronic preferences for catalysis by carboxylate groups do not translate into stereoelectronic preferences for hydrogen-bond formation.