Study of conformation and hydrogen bonds in the p-1-adamantylcalix[8]arene by IR spectroscopy and DFT

The hydrogen bonds and the conformations of calix[8]arene molecules with p-tert-butyl and p-1-adamantyl substituents were studied by infrared spectroscopy in different states. The conformations, the reactivity, the charge distribution and the IR spectra of the calixarenes were calculated by the DFT method with the PBE functional and a TZVP basis set. We compare the IR spectra of calix[8]arene molecules in the conformation of the pleated loop and the chair. The optimized geometry of the molecules reproduces the experimental X-ray data. The conformation chair is 20 kcal/mol less preferable than the conformation pleated loop. The conformation of a pleated loop is the most stable in the solid state and solution. Hydrogen bonds determine the stability of this structure. In the p-1-adamantylcalix[8]arene, stronger hydrogen bonds are realized compared to p-tert-butylcalix[8]arene. The observed IR spectra were interpreted using the calculated potential energy distribution with the quantum-chemical force constants. The theoretical absorption curves calculated for the pleated loop conformation correspond to the experimental IR spectra of the calix[8]arenes.