Raman spectra of potassium trans-4-hexenoate and conformational change on micellization

Abstract

The infrared and Raman spectra of potassium trans-4-hexenoate (PT4H) have been measured in the crystalline state and in aqueous solution. Normal coordinate calculations have been carried out to explain the vibrational spectra. For crystalline PT4H it is concluded from the vibrational spectra in the 700–100 cm^–1 region that the trans–skew (TS) and trans–cis(TC) forms coexist at 300 K and the TS form is stabilized at 100 K. For the PT4H ions in aqueous solution the TS form was found to be predominantly stabilized on micellization. In particular, the Raman spectra of a PT4H–H₂O solution in the 1700–700 cm^–1 range were investigated at various concentrations, and it was found that the stabilization of the TS form is reflected in vibrational modes characteristic of the —CHCH— and CH₂ groups. The difference Fourier-transform infrared (F.t.i.r.) spectra of PT4H–H₂O (or PT4H–D₂O) solutions have also been measured at various concentrations. The infrared absorption spectra of water were successfully cancelled out in the 1500–900 cm^–1 region for H₂O and in the 1700–1300 and 1000–700 cm^–1 regions for D₂O. The concentration dependence of the difference F.t.i.r. spectrum was used to investigate conformational changes upon micellization.