Direct observation of odd-even effect for chiral alkyl alcohols in solution using vibrational circular dichroism spectroscopy

The odd-even effect of chiral alkyl alcohols, (S)-CH3CHOHCnH2n+1 (n = 2-8), in solution state has been observed spectroscopically for the first time. The vibrational circular dichroism (VCD) bands at 1148 cm(-1) exhibit a clear odd-even effect. The observed VCD bands of (R)-(-)-2-hexanol correspond well to those predicted (population weighted). Density functional theory calculations indicate that the most prevalent conformations in solution are the all-trans forms. The odd-even effect of the VCD bands is ascribed to the alternating terminal methyl motions in the alkyl chains relative to fixed motions near the chiral center in the trans conformations. The conformational sensitivity of VCD for the chiral alcohols in the solution state may be useful for the design of liquid crystals and ligands in the future.