Doi:10.1016/S0040-4020(99)00013-7

Synthesis and Structural Studies of Some [1₄]Paracyclo-bis-(1,2)pyrazolium- and (1,3)imidazolium-phanes 

The crystal and molecular structure of [1₄]paracyclo-bis-(1,2)pyrazoliumphane dibromide (1a) has been determined. The compound exists in the solid state in the chair (C) conformation while both chair (C) and boat (B) conformations are present in solution in comparable amounts. The barrier to the C ⇌ B interconversion has been determined by ¹H NMR spectroscopy (). AM1 semiempirical calculations conveniently reproduce the difference in stability between the chair (C) and the boat (B) conformations.

[1₄]Paracyclo-bis-(1,2)pyrazolium-phane dibromide exists in the solid state in the chair conformation (X-ray crystallography) while both chair and boat conformations are present in solution in comparable amounts. The barrier to the chair boat interconversion has been determined by¹H NMR spectroscopy ().