The full assignment of the carbon-13 nuclear magnetic resonance spectrum of 5α-cholestan-3β-ol with the aid of the lanthanide shift reagent Yb(dpm)3

Abstract

Shifts induced by Yb(dpm)₃ and La(dpm)₃ in the ¹³C and ¹H n.m.r. spectra of 5α-cholestan-3β-ol are used in conjunction with off-resonance proton decoupling to assign the 27 carbon resonances. Simple shielding considerations are required to resolve ambiguities in only two pairs of resonances. Three computer-based approaches to metal ion positioning are examined, best results being obtained when the metal ion is allowed to populate, equally, sites symmetrically disposed with respect to the O–C(3)–H(3) plane. The steroid does not appear to rotate freely about the O–C(3) bond in the shift reagent–steroid complex. Spin–lattice relaxation times are presented in support of the assignments.