Computational Study of the Conformations of Syn- and Anti-Phenylquinazoline Calix[4]Arene Diether

The structures of the various conformers of syn- and anti-phenylquinazoline calix[4]arene diether (1) were optimized using molecular mechanics (MM+) and mPW1PW91/6-31G(d, p) (hybrid HF-DF) calculation methods. We analyzed the total energies and the differences in the energies of the five conformers [CONE(syn), PC(syn), 1,3-A(syn), PC(anti), 1,2-A(anti)] of the syn- and anti-atropisomers of 1. For the syn- atropisomer of 1, the 1,3-A conformer was calculated to be the most stable in the MM+ calculation, which accords with its crystal structure. The syn-1(CONE) conformer was calculated to be the most stable in the mPW1PW91 calculation, which agrees with the experimental structure in solution. For the anti-atropisomer of 1, the 1,2-A conformer was calculated to be the most stable by both the MM+ and mPW1PW91 calculation methods, which correlates very well with the experimental crystal structure of anti-1.