Exhaustive exploration of the conformational landscape of mono- and disubstituted five-membered rings by DFT and MP2 calculations

The conformational landscape of 22 different non, mono-, and disubstituted compounds with a five-membered ring was thoroughly explored by ab initio (MP2) and DFT (B3LYP and M06-2X) methods with the 6-311+G** basis set. Our results showed that the conformational preference of these compounds was governed mainly by the specific characteristics of the substituents, with a minor influence of the level of theory employed. After a detailed analysis of the computational data, we found an interesting preference of the electronegative substituents to take pseudo-axial positions, whereas alkyl groups preferred adopting the pseudo-equatorial locations. Such preferences were pronounced with MP2 and M06-2X and underestimated by B3LYP. Despite each level of theory affording different landscapes in many cases, as a general trend, we noticed that M06-2X afforded much higher correlation with the MP2 results than B3LYP.