Conformational study of erythritol and threitol in the gas state by density functional theory calculations

Abstract

Abstract-Density functional theory calculations using the B3LYP functional and the 6-311++G(d,p) basis set were carried out on the isolated molecules of erythritol and L L-threitol. For the meso isomer, a relatively large number of conformers have to be considered to describe the gas state structure. The lowest energy conformer is characterized by the establishment of a strong intramolecular H-bond between the two terminal hydroxyl groups, giving rise to a seven-membered ring and two additional weaker H-bonds between vicinal OH groups. In the case of L L-threitol, two conformers are predominant in the gas state, and both are stabilized by the formation of a cyclic system of four intramolecular hydrogen bonds involving all OH groups. The conformational stability in both diastereomers is discussed in terms of the electronic energy and of the Gibbs energy. The weighted mean enthalpy of both diastereomers in the gas state at 298.15 K was obtained from the thermodynamic data and Boltzmann populations of the low-energy conformers.

Silicon Forms a Rich Diversity of Aliphatic Polyol Complexes in Aqueous Solution

“…As was noted above, the signal at −0.29 ppm in Figure 1a corresponds to the Si−polyol complex, Q 0 -L (Scheme 3). 48 Its half-height line width (Δν 1/2 = 20 Hz) is much broader than that of Q 0 -L signals observed for simple alcohols (e.g., Δν 1/2 ≈ 1 Hz for methanol and ethanol at this temperature). 48 A logical interpretation would be that the signal represents the exchange-coalesced average of three individual resonances, arising from Si coordination at each of mannitol's nonequivalent OH groups.…”

“…48 Its half-height line width (Δν 1/2 = 20 Hz) is much broader than that of Q 0 -L signals observed for simple alcohols (e.g., Δν 1/2 ≈ 1 Hz for methanol and ethanol at this temperature). 48 A logical interpretation would be that the signal represents the exchange-coalesced average of three individual resonances, arising from Si coordination at each of mannitol's nonequivalent OH groups. Analogous broad Q 0 -L signals were detected between −0.2 and −1.2 ppm for all silicate−polyol solutions at T < 20 °C (see, e.g., Figures 1−4 and 7) except where Q 0 -L formation is suppressed by strongly competing complexation equilibria involving P 0 -and H 0 -ligand complexes (exemplified by Figures 5 and 6).…”

“…By contrast, 18 conformers make up 97% of the equilibrium population for erythritol, and none are especially dominant. 48 Interestingly, many of the low-lying erythritol conformers exhibit O−C−C− O dihedral angles for the C1−C2 and C3−C4 hydroxy pairs that lie within the range Kastele et al 41 deemed feasible for Si binding. Why then have no high-coordinate Si complexes been experimentally detected for erythritol or any other polyol which lacks threo-diol f unctionality?…”

“…Both molecules have considerable flexibility when in a free unbound state. Jesus et al 48 explored the B3LYP/6-311++G(d,p) conformational space of threitol and erythritol in the gas phase and demonstrated the existence of 15 and 18 unique backbone arrangements, respectively, of these molecules. For threitol, 98% of the equilibrium population is represented by only 8 conformers, of which three are particularly dominant.…”

Crystallization: From the Conformer to the Crystal

“…In order to simulate solvent effects, their energy was also evaluated by single-point calculations in aqueous solution using the CPCM continuum model. Details of the computational calculations are given elsewhere [69,70].…”