Collect. Czech. Chem. Commun. 1991, 56, 966-972

Infrared spectra of 2α-substituted 3-oxotriterpenoids and conformation of ring A

Jiří Klinot, Stanislav Hilgard, Jakub Krijt and Petr Olšovský

Department of Organic Chemistry, Charles University, 128 40 Prague 2


Infrared spectra of triterpenoid 19β,28-epoxy-18α-oleanane 3-ketones I - VI in the region of carbonyl stretching frequencies have been studied. Comparison of the spectra of crystals with those of solutions in various solvents, together with comparison of fundamental C=O frequencies with their first overtone leads to the conclusion that the doublet character of the carbonyl band in the solution of ketones I - IV with polar substituent in position 2α is caused by the chair-boat equilibrium of the ring A.