Anti-parallel dimer and tetramer formation of propylene carbonate

Abstract

Raman scattering and infrared (IR) absorption spectra of enantiopure (R)-propylene carbonate ((R)PC) and racemic propylene carbonate (PC) were recorded at room temperature, 25 °C, in benzene (Bz) solution and in the pure liquid state to investigate the presence of dimers and other higher order intermolecular associations. (R)PC and PC both demonstrated a strong C=O stretching vibrational band. The band exhibited changes in its shape and resonance wavenumber highly dependent on the concentrations of PCs, whereas a difference between the chirality of (R)PC and PC had little influence. In an extremely dilute condition, doubly split bands were observed at 1807 and 1820 cm-1 in both Raman and IR spectra, which are assigned to the characteristic bands of isolated monomeric PCs. An additional band appeared at 1795 cm-1 in a dilute to concentrated regime, and its magnitude strengthened with increasing concentrations accompanied with slight increasing in the magnitude of 1807 cm-1 band in Raman spectra, while an increase in the magnitude of 1807 cm-1 band was clearly greater than that of 1795 cm-1 band in IR spectra. The spectrum changes at 1795 and 1807 cm-1 were attributed to characteristics of anti-parallel dimer formation of PCs caused by strong dipole-dipole interactions between C=O groups. Moreover, another additional signal was clearly observed at 1780-1790 cm-1 in a concentrated regime, and became the primary signal in the pure liquid state with slight increasing in the intensity of 1795 cm-1 band in Raman spectra. On the other hand, in IR spectra the observed increasing of 1780-1790 cm-1 band was much less than that of 1795 cm-1 band. These newly found spectrum changes in the concentrated regime are attributed to the formation of anti-parallel tetramers of PCs based on the characteristics of band selection rule found in Raman and IR spectra. Equilibrium constants for the anti-parallel dimer (KD) and tetramer formation (KT) of PCs in Bz solution and in the pure liquid state were also determined using the Raman and IR data assuming chemical processes: 4PC ↔ 2(PC)2 ↔ (PC)4.

Tailoring intermolecular interactions to develop a low-temperature electrolyte system consisting of 1-butyl-3-methylimidazolium iodide and organic solvents

“… 45 In comparison to GBL, which can be viewed as the primary source to form hydrogen bonding with the imidazolium cation in our developed system, the hydrogen bonding associated with PC was much weaker and more subtle since PC is known to demonstrate strong dipole–dipole interactions via its carbonyl group and form local structures among itself. 46,47 When PC was incorporated in the mixture, we hypothesized that the overall electronegative environment of its carbonyl groups was altered by more than a single factor of hydrogen bonding, and therefore caused a minor blue shift. Thus, the FTIR results validated the modified molecular interactions in the mixture system and further details of the targeted ion–solvent interactions were subsequently unveiled by NMR spectroscopy.…”

Molecular Structure, Chemical Exchange, and Conductivity Mechanism of High Concentration LiTFSI Electrolytes

“…The dimer formation by BC carbonate molecules in the solvation shell of Li + is not new since it has been previously observed in a LiTFSI:EC solvate 26 and predicted theoretically in another cyclic carbonate, propylene carbonate. 79 In the solvate structure, two EC molecules coordinating two different lithium centers are observed to be an arrangement where both EC molecules are almost parallel to each other but with their dipoles are pointing in opposite directions. 26 This type of structure was predicted to have a stabilization energy of ∼20 kJ/mol.…”

Quadrupole Contribution of C═O Vibrational Band in Sum Frequency Generation Spectra of Organic Carbonates

“…PC molecules are known to form antiparallel dimers in liquid phase. 27,29,30 Tagawa et al assigned the monomer component at 1807−1820 cm −1 and dimer (or high-order oligomers) at 1780−1795 cm −1 by their spectral analysis of IR and Raman of liquid PC. 27 Therefore, we evaluated the contribution of PC dimer on χ IQB by the present method using quantum chemical calculations and found that an antiparallel dimer has a contribution smaller than twice that of the monomer.…”

“…27,29,30 Tagawa et al assigned the monomer component at 1807−1820 cm −1 and dimer (or high-order oligomers) at 1780−1795 cm −1 by their spectral analysis of IR and Raman of liquid PC. 27 Therefore, we evaluated the contribution of PC dimer on χ IQB by the present method using quantum chemical calculations and found that an antiparallel dimer has a contribution smaller than twice that of the monomer. This result indicates that the low-frequency component of the dimer is less emphasized in the χ IQB spectrum, which leads to an apparent blue shift of its line shape.…”

“…(a) Refractive index of PC n (ω) in the CO stretching region (black), and f x (ω) = f y (ω) (red) and f z (ω) (blue) in eq . (b) (Black) experimental IR absorbance spectrum α­(ω) times n (ω) of PC liquid. (Red) estimated line shape of Im­[χ IQB ] by considering different local field factors.…”