A study of hydrogen bonds in p-substituted calix[4]-and calix[6]arenes by ab initio and electron density functional methods

RHF/3-21G and B3LYP/3-21G methods are used to calculate the hydrogen bond energies in calix[4]-, calix[6]-, p-fluorocalix[4]-, p-fluorocalix[6]-, p-chlorocalix[4]-, p-chlorocalix[6]-, p-bromocalix[4]-, pbromocalix[6]-, p-iodocalix[4]-, p-iodocalix[6]-arenes and a number of other p-substituted calix[4]- and calix[6]arenes (R = Me, OMe, NO₂, Ac, NH₂, CN, N₂⁺). The calculations along with the structural data give evidence of the cooperative effect of hydrogen bonding. Multiple correlation (p ≥ 0.9) between the pairs of Hammett substituent constants and the calculated values of hydrogen bond energies in the corresponding p-substituted calixarenes is found. It is predicted that in the presence of weak bases and in aprotic solvents as well as in the gas phase, the nucleophilic substitution reaction involving p-halogen calix[6]arenes should proceed through diastereomeric transition states.