Conformations of 1,2-Ethanediol

Display electrostatic potential maps for both anti and gauche conformers of 1,2-ethanediol. Do you see any examples of destabilizing interactions (between like charges) or stabilizing interactions (between unlike charges) in either conformer Are you able to explain the observed conformational preference  

Electrostatic potential map for trails-1,2-ethanediol shows negatively-charged regions (in red) and positively-charged regions (in blue). 

Alcohols are typically very weak acids with pKa values in the range of 7 - 20 (compared with a pK value of 4.8 for acetic acid). 

Display and compare electrostatic potential maps for methanol, ethanol, 2-propanol and trifluoroethanol. Identify the acidic sites as those where the potential is most positive and, assuming that the more positive the potential the more acidic the site, rank the acidities of the compounds. Does increased alkyl substitution have a significant effect on acid strength What is the effect of replacing the methyl group in ethanol by a trifluoromethyl group Why Do you find a correlation between the most positive value of the potential and the experimental pKa  

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Construct molecular models of the gauche and anti conformations of 1 2 ethanediol and explore the possibility of intramolecular hydrogen bond formation in each one... 

Table 5-1. Relative energies (kcal mol ) of 1,2-ethanediol and methoxymethanol conformations, and RMS error with respect to MP2 level of theory...

Teppen, B. J., M. Cao, R. F. Frey, C. Van Alsenoy, D. M. Miller, and L. Schafer. 1994a. An Investigation into Intramolecular Hydrogen Bonding Impact of Basis Set and Electron Correlation on the Ab Initio Conformational Analysis of 1,2-Ethanediol and 1,2,3-Propanetriol. J. Mol. Struct. (Theochem) 314,169-190. 

C. J. Cramer and D. G. Truhlar, Quantum chemical conformational analysis of 1,2-ethanediol Correlation and solvation effects on the tendency to form internal hydrogen bonds in the gas phase and aqueous solution, J. Am. Chem. Soc. 116 3892 (1994). 

The four lowest energy complexes of 1,2-ethanediol with one water molecule, 3a-d comprise 73.4 percent of the total complex population. The two dominant complexes, 3a and 3b, have the same underlying tG+g conformation of... 

Csonka, G. I. Csizmadia, I. G. Density functional conformational analysis of 1,2-ethanediol, Chem. Phys. Lett. 1995, 243, 419-428. 

O. Guvench and A. D. MacKerell, Jr., Quantum mechanical analysis of 1,2-ethanediol conformational energetics and hydrogen bonding, /. Phys. Chem. A, 110 (2006) 9934-9939. 

So ihe conformational ratio of 2-chloroethanol should be more like that of 1,2-ethanediol than 1,2-dichIoroethane, in which hydrogen bonding is absent. ... 

During the quantum mechanical conformational analysis of 1,2-ethanediol, aqueous solvation effects were taken into account via SMla/AMl, SM2/AM1 and SM3/PM3 methods. By adding calculated fiee energies of solvation to gas-phase free energies it was found that the trans population increased from 2% (in gas phase) to 12% (in water solvent) and that the portion of conformers having no internal hydrogen bond increased from 17% to 25%. The calculated results were in reasonable agreement with experimental data both in the gas phase and in aqueous solution [64]. 

Ethanediol, like n-butane, exists as an equilibrium mixture of two distinct conformers anti (OCCO dihedral angle = 180°) and gauche (OCCO dihedral angle 60°). 

Examine space-filling models for the two conformers and identify any likely unfavorable nonbonded interactions. Based on steric effects, which conformer would you anticipate would be the more stable Compare energies of anti-1,2-ethanediol and gauche-1,2-ethanediol to see if you are correct. Is this the same ordering of conformer energies as seen for n-butane (see Chapter 5, Problem 3)7... 

In order to consider the effect of solvation on the conformational preference of D-glucose, we will first examine two simple analogs 1,2-ethanediol and... 

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