Abstract: To produce defined isomer mixtures of compounds with spirocyclic beta-aminocarboxyl and/or beta-aminocarbonyl systems the invention supposes that they be dissolved in solvents which have good dissolving power for these compounds, whose relative permittivity is sufficient to stabilize the amphoteric intermediates occuring in isomerization, which as proton donors constitute hydrogen bridges, whose basicity is less than that of the compounds for isomerization and whose boiling point is so high that an adequate reaction speed can be attained by raising temperature. Further, the invention proposes that the isomerization be prevented, influenced, or terminated by altering at least one of these factors and or by altering the temperature.