Proton tunneling in calix[4]arenes: a theoretical investigation

The structure, energetics and vibrational force field of calix[4]arene (CA) are calculated for the chiral equilibrium configuration and the symmetric transition state for coherent quadruple proton transfer. The corresponding proton and deuteron tunneling splittings are evaluated with the instanton approach. The calculated zero-point proton tunneling splitting is compared with data reported for low-temperature NMR relaxometry experiments.