Conformational energy diagram

Fig. 1. Conformational energy diagram for the alanine dipeptide (adapted from Ramachandran et al., 1963). Energy contours are drawn at intervals of 1 kcal mol-1. The potential energy minima for p, ofR, and aL are labeled. The dependence of the sequential d (i, i + 1) distance (in A) on the 0 and 0 dihedral angles (Billeter etal., 1982) is shown as a set of contours labeled according to interproton distance at the right of the figure. The da (i, i + 1) distance depends only on 0 for trans peptide bonds (Wright et al., 1988) and is represented as a series of contours parallel to the 0 axis. Reproduced from Dyson and Wright (1991). Ann. Rev. Biophys. Chem. 20, 519-538, with permission from Annual Reviews.

Higher + Electronic + Interaction with the environment Spatio-temporal structure (flexibility, conformation) Electronic properties (electron distribution, polarizability, ionisation) Solvation, hydration, partitioning, intermolecular interactions Conformational energy diagrams, computer display Molecular orbitals, electrostatic potential maps Computer display... 

Conformational energy diagrams of L-Ala show the presence of minima for 4)/ I -dihedral angle combinations representing both a-helix and p-structure. The energy of these two minima is about the same. 

A potential energy diagram for nng inversion m cyclohexane is shown m Figure 3 18 In the first step the chair conformation is converted to a skew boat which then proceeds to the inverted chair m the second step The skew boat conformation is an inter mediate in the process of ring inversion Unlike a transition state an intermediate is not a potential energy maximum but is a local minimum on the potential energy profile... 

Sketch a potential energy diagram for rotation around a carbon-carbon bond in propane. Clearly identify each potential energy maximum and minimum with a structural formula that shows the conformation of propane at that point. Does your diagram more closely resemble that of ethane or of butane Would you expect the activation energy for bond rotation in propane to be more than or less than that of ethane Of butane ... 

FIGURE 3.18 Energy diagram showing the interconversion of various conformations of cyclohexane. 

Construct a qualitative potential-energy diagram for rotation about the C-C bond of i,2-dibromoethane. Which conformation would you expect to be more stable Label the anti and gauche conformations of 1,2-dibromoethane. 

Figure 15 (A) Polyethylene chain in planar zig-zag conformation. (B) Energy diagram of...

Figure 2. A contour diagram of the conformational energy of p-cellobiose computed from eqn. (6) holfing constant all variables except < ), v see ref. 5 for details. The rigid glucose residue geometry was taken from ref. 23, and the valence angle p at 04 was chosen as 116 in accordance with the results of pertinent crystal structure determinations. Contours are drawn at 2,4, 6, 8,10,25, and 50 kcal/mol above the absolute minimum located near ( ), v = -20 , -30 higher energy contours are omitted.

Figure 18. Contour diagram for the conformational energy of the terminal residue of a trisaccharide segment of the a-(1 2)-L-fucan constrained to satisfy the helical condition - see text for details. Contours are drawn at absolute energies 2,4, 5, 10, 25, and 50 kcal/mol.

Energy diagrams for bond rotation in 2,2,4,4-tetramethylpentane, 2,2,4,4,6,6-hexamethytheptane, and 2,2,4,4,6,6,8,8-octamethylnonane are generated in a completely a priori manner. A relatively simple conformational model gives a good representation of the conformations calculated, and permits a statistical mechanical calculation of the characteristic ratio. 

Figure 3.21 Potential energy diagram of DMABN as a function of the twist angle of the nitrogen lone pair orbital. In the planar conformation the states JLa and 1 Lb are the observable spectroscopic states these give rise to the states A (TICT) and B through 9(T internal rotation...

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