Studies of C-21 proton NMR behavior in a homologous series of cholest-5-ene-3, 21-diol type molecule
A homologous series of cholest-5-ene-3,21-diol type molecules in which the alkyl side chain was varied were synthesized and NMR spectra were obtained. After appropriate calculations and comparisons, possible configurations of the compounds and reaction mechanisms and pathways for their syntheses were proposed to account for the experimental observations. A previously observed NMR singlet for the two methylene protons on the primary alcohol group appeared to be the result of a small difference of chemical shift values and coupling constants for two methylene protons. Differences between comparatively free rotation and more restrictive degrees of freedom around C-20(21) or even the C-17(20) bonds are proposed as one of the reasons responsible for the observation. Also, small coupling constants generated by dihedral angles of the C-21 protons with the C-20 proton and the attachment of an electronegative hydroxy group are considered.