Modelling conformations and IR spectra of p-tert-butylthiacalix[4]arene tetraester using DFT method

The infrared spectra of the cone, partial cone and 1,3-alternate conformers of p-tert-butyltetrakis(ethoxycarbonyl)methoxytetrathiacalix4]arene (TEMT) have been recorded. The structural optimization and normal mode analysis were performed for this molecule on the basis of the density functional theory. These calculations gave the frequencies of vibrations and infrared intensities for the cone, partial cone (paco) and 1,3-alternate (1,3-alt) conformers. The energy difference between the paco and 1,3-alt conformers is 3.1 kcal/mol. The cone conformer is likely to be less stable compared to the paco and 1,3-alt conformers. The calculated in gas phase dipole moments 5.65, 3.33, and 0.02 D for the cone, paco and 1,3-alt conformers of the TEMT are in good accordance with theoretical values for the thiacalix4]arene. Complete assignments were made for the experimental IR spectra of all conformers. The softness of sulphur atoms to nucleophilic and electrophilic attack is higher than softness of oxygen atoms of ester groups in the lower rim. The bands characteristic for each conformation were defined. IR spectroscopy combined with DFT computation provides unique detailed information about the structure of the technologically relevant materials, which could not be obtained before with any other technique.