Conformational Equilibria of TADDOL-s in Solution Investigated by Vibrational Circular Dichroism

Six enantiomeric pairs of TADDOL-s gathered in two series with either methyl (series A) or phenyl (series B) substituent in 2-position of the dioxolane ring were studied by vibrational circular dichroism (VCD). Experimental IR and VCD spectra associated with density functional theory (DFT) calculations showed that the two series exhibit quite different conformations in solution. In series A, the conformer with anti C-O bonds and stabilized by intramolecular OH ... OH hydrogen bonding prevails, whereas in series B the conformer with gauche C-O bonds and intramolecular OH ... pi hydrogen bonding is favored. The shape and sign of the VCD bands in the O-H stretching region revealing the nature of the intramolecular hydrogen bonding were clearly identified. Polarimetric measurements showed that, within the same absolute configuration, compounds in series A and in series B have opposite signs of optical rotation. Chirality 22:E115-E122, 2010. (c) 2010 Wiley-Liss, Inc.