Influence of conformation on the electronic structure of thiacalixarenes according to DFT calculations and X-ray emission spectroscopy

The DFT calculations of different thiacalix[4]arenes show that the conformation and geometry of arene core mainly determine the difference in electronic density distribution (frontier occupied MO and ESP charges) between “cone” and “1,3-alternate” conformation. The key factor is orientation of benzene rings relative to average plane through bridging sulfur atoms. Calculated structure of frontier orbitals was verified by experimental sulfur Kβ spectra, calculated spectra reproducing main features of experimental ones. Difference in HOMO and ESP distribution on carbon atoms in benzene rings for “cone” and “1,3-alternate” conformers correlates with earlier reported data on regioselectivity of electrophilic substitution in these compounds.