Structure, Conformational Equilibrium, and Proton Affinity of Calix[4]arene by Density Functional Theory

Density functional theory results for the structure and conformational equilibrium of four calix[4]arene conformers are reported. The results are compared with experiment, force field, and semiempirical molecular orbital calculations. The energy difference between the two most stable conformers of calix[4]arene (cone and partial-cone) is 10 kcal mol -1 at the BLYP/6-31G** level with the geometries optimized at BLYP/6-31G*. For the most stable conformer, results for the protonated structure are also reported. Electrostatic potential surfaces for the cone calix[4]arene and the corresponding tetra-O−H-depleted structure have been calculated. It is suggested that their representation may be of relevance to understand the known ability of calix[ n ]arene systems to form complexes with charged species in host−guest chemistry.