Ethanol dimerization

Gonzales, L., Mo, O., Yafiez, M., 1999, Density Functional Theory Study on Ethanol Dimers and Cychc Ethanol Trimers , J. Chem. Phys., Ill, 3855. 

If both alcohol monomers forming a dimer are on average achiral, one may still have chirality synchronization events, where the two monomers match their transient chiral conformations when they bind to each other. A particularly simple example is that of ethanol dimer, where the lowest-energy conformer involves two gauche monomers of the same helicity [80,91]. However, the energy difference to other conformers is so small that efficient isomerizing collisions in a supersonic jet expansion are required to favor the lowest-energy form over the others. A more... 

Microwave spectroscopy is probably the ultimate tool to study small alcohol clusters in vacuum isolation. With the help of isotope substitution and auxiliary quantum chemical calculations, it provides structural insights and quantitative bond parameters for alcohol clusters [117, 143], The methyl rotors that are omnipresent in organic alcohols complicate the analysis, so that not many alcohol clusters have been studied with this technique and its higher-frequency variants. The studied systems include methanol dimer [143], ethanol dimer [91], butan-2-ol dimer [117], and mixed dimers such as propylene oxide with ethanol [144]. The study of alcohol monomers with intramolecular hydrogen-bond-like interactions [102, 110, 129, 145 147] must be mentioned in this context. In a broader sense, this also applies to isolated ra-alkanols, where a weak Cy H O hydrogen bond stabilizes certain conformations [69,102]. Microwave techniques can also be used to unravel the information contained in the IR spectrum of clusters with high sensitivity [148], Furthermore, high-resolution UV spectroscopy can provide accurate structural information in suitable systems [149, 150] and thus complement microwave spectroscopy. 

The O H stretching spectra of ethanol trimers and larger clusters cannot be conformationally resolved in a slit jet expansion [65, 77, 157], VUV-IR spectra [184] are even broader, sometimes by an order of magnitude, and band maxima deviate systematically by up to +50 cm 1 from the direct absorption spectra. We note that ethanol dimers and clusters have also been postulated in dilute aqueous solution and discussed in the context of the density anomaly of water ethanol mixtures [227], Recently, we have succeeded in assigning Raman OH stretching band transitions in ethanol-water, ethanol water, and ethanol water2 near 3550, 3410, and 3430cm, respectively [228],... 

S. Coussan, M. E. Alikhani, J. P. Perchard, and W. Q. Zheng, Infrared induced isomerization of ethanol dimers trapped in argon and nitrogen matrices Monochromatic irradiation experiments and DFT calculations. J. Phys. Chem. A 104, 5475 5483 (2000). 

M. Nedic, T. N. Wassermann, Z. Xue, P. Zielke, M. A. Suhm, Raman spectroscopic evidence for the most stable water/ethanol dimer and for the negative mixing energy in cold water/ethanol trimers. Phys. Chem. Chem. Phys. 10, 5953 5956 (2008). 

Main reaction paths of the thermal desorption of ethanol are proposed in Scheme 5. The species observed directly by NMR spectrscopy are surrounded by broken lines. At temperatures less than 323 K, the dehydration did not proceed, and only reversible desorption took place. The protonated ethanol dimer is transformed into protonated ether at temperatures exceeding 323 K. Diethyl ether is formed only in the gas phase by replacement with ethanol. Protonated ethanol monomer probably gives ethylene via the ethoxide at temperatures exceeding 333 K (169). 

Fig. 43. Transformation of protonated ethanol dimer in HjPWuO, by heat treatment. Solid-state l3C CP/MAS NMR spectra were obtained by using high purity, 3C ethanol (a) Dimer, (b) 333 K, (c) 343 K, (d) 363 K, (e) 373 K, (f) 423 K. Reprinted with permission from Ref. 169. Copyright 1992 American Chemical Society.

Ab-initio harmonic analysis of large-amplitude motions in ethanol dimers... 

The heteropolyanion stabilizes protonated intermediates by coordination in solution and the pseudoliquid phase as well as on the surface, thus lowering the activation energy and accelerating reactions. Several protonated intermediates including the protonated ethanol dimer and monomer [18], the protonated pyridine dimer [12, 19], and protonated methanol [20] have been detected in the pseudoliquid phase directly by use of X-ray diffraction (XRD), IR or solid-state NMR. In solid-state H NMR, the chemical shift for the protonated ethanol dimer, (C2HsOH)2H+ is 9.5 ppm down-field from tetramethylsilane, which lies in the range of supcracids reported by Olah et al. [18]. This fact also supports the strong acidity of heteropolyacids. 

L. Gonzalez, O. Mo, and M. Yanez, Density functional theory study on ethanol dimers and cyclic ethanol trimers, /. Chem. Phys. Ill, 3855-3861 (1999). 

Cooperative Effect. - Gonzalez et studied the structure and the relative stability of the ethanol dimer and the cyclic ethanol trimer using DFT. Cooperative effects are reflected in the electron density of the BCPs. 

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