The effects of OH groups on the relative stabilities and the structures of four conformers of OH-depleted calixarenes are discussed on the basis of a computational method using molecular mechanics (MM3(92)) calculations. The results are compared with various NMR spectroscopic experiments. From these studies, it is found that the calixarene framework with no OH group in the lower rim (tetra-OH-depleted calixarenes: 4a and 4b) favors a cone conformation with C4 symmetry and the changes in the relative stabilities in calixarenes with OH-groups are due to the formation of stable hydrogen bonds and/or the relaxation of the steric crowding around OH-substituents in a lower rim site. NMR studies suggest that mono-OH-depleted calixarene 1b forms intra- and intermolecular hydrogen bonds among phenolic OH groups, while di- and tri-OH-depleted calixarenes (2b and 3b) scarcely form it. They also show that the ring inversion barriers of calixarenes increase with the number of OH groups in 25, 26, 27 or 28-position.
All Science Journal Classification (ASJC) codes
- Drug Discovery
- Organic Chemistry