1,2-ethanediol conformations

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. 

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... 

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... 

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 ... 

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). 

Using the same level of approximation calculations on 1-methoxyethanol and 1,1-ethanediol [70] showed that the conformations following the exo anomeric effect are those with the lowest energy and thus supported the explanation given above for the discrepancies resulting from the lack of a C-2 atom in the calculation of the 1-O-acyl fragments. 

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... 

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. 

Use SpartanView to compare the energies of gauche and anti conformers of butane. 1,2-ethanediol, and 1,2-dimethoxyethane. Which molecules prefer the anti conformation. about the C-C bond, and which prefer the gauche Examine the electrostatic potential map of any molecule that prefers the gauche conformation, and explain why this conformation is preferred. 

---