Dimer self-association via hydrogen bonding: Measurement and comparison of binding constants with 2-amidopyrimidine derivatives

A method based on 1H NMR was used to measure the self-assembly equilibrium constants for three acylated derivatives of 2-aminopyrimidine: 2-acetamidopyrimidine (1), 2-isopropylamidopyrimidine (2), and 2-neopentylamidopyrimidine (3). The synthesis of the latter two compounds is described. The self-association constant decreases from 1 to 2 to 3, which is attributed to the syn/anti conformational preference of the amide bond. For 1, complexation with chloroform must be included in order to explain the observed chemical shift values. Complementary density functional theory calculations (MP2/cc-pVTZ//B3LYP-D/cc-pVDZ) suggest a direct relationship between conformational preference of the amide bond and the self-assembly constant.