Study of Some Benzo-Crown Ethers By NMR and Molecular Mechanics

The ¹H NMR spectra of DB18C6, B15C5 and B15C5·Mg（ClO₄）₂ were obtained and the torsional angles of the—O—CH₂—CH₂—O—fragment of the crown ethers were calculated by using the Karplus formula. The Molecular Mechanics was used to calculate the conformations of the crown ethers. The most stable conformations were given. Results show that the oxygen atoms of the crown ethers are located on a mean plane and form an approximate regular polygon. In the complex B15C5·Mg（ClO₄）₂, Mg⁺⁺ is located on the mean plane of the five oxygen atoms and at the center of the regular polygon. The structures of the crown ethers in solution are different from those in crystal and the changes of the torsional angels of the—O—CH₂—CH₂—O—fragment were given. There are gauche—and anticonformations of the—O—CH₂—CH₂—O—fragment in crystal of DB18C6, but only gauche—conformation is found in the solution.