Potential conformers

Jensen, J.H. Gordon, M.S. The conformational potential energy surface of glycine A... 

The researchers established that the potential energy surface is dependent on the basis set (the description of individual atomic orbitals). Using an ab initio method (6-3IG ), they found eight Cg stationary points for the conformational potential energy surface, including four minima. They also found four minima of Cg symmetry. Both the AMI and PM3 semi-empirical methods found three minima. Only one of these minima corresponded to the 6-3IG conformational potential energy surface. 

Lelj, F., C. Adamo, and V. Barone. 1994. Role of Hartree-Fock exchange in density functional theory. Some aspects of the conformational potential energy surface of glycine in the gas phase. Chem. Phys. Lett. 230, 189. 

Perczel, A., W. Viviani, and I. G. Csizmadia. 1992. Peptide Conformational Potential Energy Surfaces and Their Relevance to Protein Folding in Molecular Aspects of Biotechnology Computational Models and Theories, Bertran, J., ed., Kluwer Academic Publishers, 39-82. 

Viviani, W., J.-L. Rivail, A. Perczel, and I. G. Csizmadia. 1993b. Peptide Models. 3. Conformational Potential Energy Hypersurface of Formyl-L-valinamide. J. Am. Chem. Soc. 115, 8321-8329. 

Fig. 21. (a) The local minima in a hypothetical conformational potential given by the solid line, with three conformational substates. The bottoms of the wells are parameterized by power laws, V, proportional to three values of a are shown in dashed lines, (b) The temperature dependence of the vibrational and collective motion x )c)... 

This section presents X-ray diffraction, dynamic NMR and theoretical data on the conformations of heterocyclic eight-membered rings. Ideally, it would be desirable to know the whole conformational potential energy surface of the ground electronic state of a molecule. In practice, the lowest (and perhaps the second lowest) energy conformation can be more or less characterized, and some conformational energy barriers can be determined and calculated. 

A semiempirical force field is constructed for the calculation of conformational potential energies of unstrained, acyclic, aliphatic aldehydes and ketones, taking solvent effects into consideration. Detailed conformational calculations for fitting and testing the necessary parameters are done. The results are incorporated into a RIS scheme for polylmethyl vinyl ketonels. 

The molecular mechanism of local segment rotations can be explained by the occurrence of twin reversals [33, 34] which are induced thermally due to the unusual course of the conformational potential [35]. Those twin reversals are torsion defects causing the helix conformation to change from left-handed to right-handed and vice versa. They are built into the PTFE helix without changing the direction of the molecular long axis (Fig. 23). Additionally, the long... 

Figure 4. Conformational potential energy maps for rotation...

Figure 6. Conformational potential energy map from sucrose parameters with hydrogens of intramolecular H-bonds removed...

Butane can exist in an infinite number of conformations (we have chosen to show only the six most significant) but has only three conformers (potential energy minima)— the two synclinal (gauche) conformations and the anti-periplanar conformation. 

Conformation Potential Energy Vibrational Energy °W T Vibrational Entropy (TS) Free Energy AAtot... 

Monosaccharides exist chiefly in the six-membered pyranose form and in the flve-membered furanose form, both of which adopt puckered shapes to minimize eclipsing interactions. These puckered shapes are most commonly described in terms of the shapes of the symmetrical conformations adopted by the analogous hydrocarbons, cyclohexane and cyclopentane [8,9,10,11], but may also be described in terms of puckering parameters [12,13,14]. Minima on the conformational potential energy surface are called conformers. 

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