Molecular self-assembling of chiral and racemic butan-2-ol in carbon tetrachloride solutions

The self-association of (R)-, (S)- and (RS)-butan-2-ol in their carbon tetr achloride solutions was studied through the mid-infrared (mid-IR) and near- infrared (NIR) spectroscopic observations. The mid-IR and NIR spectra for e ach chiral butan-2-ol were compared with those for the racemic (RS)-butan-3 -ol. Although it has been reported that the hydrogen bonding among the chir al butan-2-ol molecules was stronger than that among the racemic ones, any distinguishable differences between the chiral and the racemic butan-2-ol i n CCl4 solution or even in their pure liquid state were not observed both i n their mid-IR and NIR spectra. A superior analytical method, assuming a su ccessive association process for the alcohol molecules, was applied to the analysis of the sharp band at 3630 cm(-1) (the OH-stretching vibration mode attributed to free OH-monomer) for the (R)-, (S)- or (RS)-butan-2-ol in CC l4. The mean association number [N] for each alcohol increased with increas ing in concentration until 0.12 mol dm(-3) and then becomes constant (about four). On the other hand, Zanker's plotting method, assuming an equilibriu m between monomers and only one kind of polymer species, was also applied t o the analysis of the above spectroscopic results; the association number n evaluated from the Zanker's method fairly agreed with the [N] value in the concentration region of 0.12-0.60 mol dm(-3). (C) 1999 Elsevier Science B. V. All rights reserved.