Combined NMR spectroscopy and molecular mechanics studies of OH-depleted calix[4]arenes: On the influence of OH groups on the relative stability of calix[4]arene conformers

Takaaki Harada, Fumio Ohseto, Seiji Shinkai

Research output: Contribution to journalArticle

49 Citations (Scopus)

Abstract

The effects of OH groups on the relative stabilities and the structures of four conformers of OH-depleted calix[4]arenes 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 calix[4]arene framework with no OH group in the lower rim (tetra-OH-depleted calix[4]arenes: 4a and 4b) favors a cone conformation with C4 symmetry and the changes in the relative stabilities in calix[4]arenes 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 calix[4]arene 1b forms intra- and intermolecular hydrogen bonds among phenolic OH groups, while di- and tri-OH-depleted calix[4]arenes (2b and 3b) scarcely form it. They also show that the ring inversion barriers of calix[4]arenes increase with the number of OH groups in 25, 26, 27 or 28-position.

Original languageEnglish
Pages (from-to)13377-13394
Number of pages18
JournalTetrahedron
Volume50
Issue number47
DOIs
Publication statusPublished - 1994
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Drug Discovery
  • Organic Chemistry

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