1. The automatic assembly of dilactones from α,α′-dihydroxyglutaric acids and their derivatives is controlled not only by configuration (from the d, l and not the meso form) but also by conformation and is not realized in the presence of α,α′-substituents having predominantly pseudoequatorial orientation in the corresponding monolactone. Thus, γ-crotonolactone is formed instead of the expected dilactone during the thermolysis of d,l-α,α′-dihydroxyglutaric acid. 2. The diastereomers of α,α′-dibromoglutaric acid and the d,l-forms (in contrast to the meso form) of α,α′-dihydroxyglutaric acid and their esters are conformationally uniform in the case where there is no intramolecular hydrogen bond. 3. The meso forms of the conformationally uniform α,α′-disubstituted glutaric acids differ from the d,l-forms in the nonequivalence of the JCH spin-spin coupling constants with the protons of the CH2 group. 4. Pseudoaxial preference was detected for the CO2H and CO2Me groups in trans-2-hydroxy-4-carboxy-γ-butyrolactone and its methyl ester respectively.