Systematic Evaluation of the Conformational Properties of Aliphatic ω-Hydroxy Acids

A systematic conformational study of ω-hydroxy acids, HO−(CH₂)_n−COOH with n ranging from 2 to 5, has been performed using quantum mechanical calculations at the MP2 level. To distinguish between intrinsic and environmentally induced conformational preferences, calculations have been carried out in both gas phase and chloroform solution, a polarizable continuum solvation model being used to represent the latter. Results indicate a consistent conformational behavior, as reflects the feature that the lowest energy minimum for n = 2, 3, 4, and 5 corresponds to the g⁺g^-t, g⁺g⁺g^-t, g^-g⁺g⁺g^-t, and g⁺g^-g⁺g⁺g^-t conformations, respectively. Furthermore, the stability of the extended and semiextended conformations increases systematically with the size of the central aliphatic segment. The relationship between the size of the aliphatic segment and the stability of folded conformations is analyzed and discussed.