Solvent and Structural Effects on Hydrogen Bonds in Some Amides and Barbiturates. An Additive Scheme for the Stability of Corresponding Host‐Guest Complexes

NMR Shift titrations with 2,6‐diacyldiaminopyridines as well as with the parent benzene derivative and barbiturates indicate strong hydrogen bond attenuation by steric hindrance, by flexible side chains, and by chloroform as solvent. Analysis of unhindered associations and of corresponding host‐guest complexes reported in the literature shows a linear correlation of complexation free energy Δ G ° with the number n of hydrogen bonds for n > 1, which amounts to Δ G ° = (5 ± 1) kJ/(mol · n ) in CDCl 3 ; this value is expected to increase in carbon tetrachloride to Δ G ° ≈ 10 kJ/(mol · n ) as judged by extrapolation from 2 measurements.