The pseudorotation of cycloheptane—I

Abstract

The pseudorotation of cycloheptane is described by means of the Fourier expansion of the endocyclic torsion angle ω i = A sin φ j + B sin 3φ j + C sin 5φ j + D sin 7φ j; φ j = Δ/2 + 2πj/7; j = 0, 1,...,6; i = 2j + 4, mod 7 and Δ being a phase angle. The topography of the pseudorotational itineries for the chair/twist-chair and the boat/twist-boat families is discussed. X-ray diffraction data concerning the geometry of 7-membered rings occurring in fused ring compounds are analysed by means of the proposed relationship. The least squares procedure for evaluation of the parameters A, B, C and D is given in an appendix. The calcium salt of cycloheptane car☐ylic acid, (C 7H 13·COO) 2Ca·5H 2O in solid state, displays disorder closely related to pseudorotation. Preliminary X-ray diffraction data of this structure (to be published elsewhere) are given.