A study of hydrogen bonds in <Emphasis Type="Italic">p</Emphasis>-substituted calix[4]-and calix[6]arenes by <Emphasis Type="Italic">ab initio</Emphasis> and electron density functional methods

RHF/3-21G and B3LYP/3-21G methods are used to calculate the hydrogen bond energies in calix4]-, calix6]-, p-fluorocalix4]-, p-fluorocalix6]-, p-chlorocalix4]-, p-chlorocalix6]-, p-bromocalix4]-, pbromocalix6]-, p-iodocalix4]-, p-iodocalix6]-arenes and a number of other p-substituted calix4]- and calix6]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 calix6]arenes should proceed through diastereomeric transition states.