Newman strain

The 1,5-interaction between two nonhydrogen atoms on and N or CO (Newman strain) constitutes the most important repulsive interaction in proteins. One first draws the formal C = N double bond in the Newman projection with up and N down. At ( ) = 0 both carbonyl... 

There are two fundamental conformations that are essentially strain-free, namely ( ) = 120° and / = 120° (Figs. 9.2.4 and 9.2.5 only linear conformation, sheet) and = -60° (a-helix) (Fig. 9.2.6). They have minimal Pitzer and Newman strains, and the linear conformer is even free of allylic strain. Furthermore, interchain (intercatenar) NHCO-hydrogen bonding is optimal in the ( ) = -120° and / = -60° conformation. The allylic strain present in the latter conformer is overcome by this favorable dipole interaction in the right-handed helix (Fig. 9.2.6) (Ramachandran and Sasisekharan, 1968). 

FIGURE 3 6 The gauche and anti conformations of butane shown as ball and spoke mod els left) and as Newman projections right) The gauche conformation is less stable than the anti because of the van der Waals strain between the methyl groups... 

Problem 3.18 Draw a Newman projection along the C2-C3 bond of the following conformation of 2,3-dimethylbutane, and calculate a total strain energy ... 

Increased substitution around a bond leads to increased strain. Take the four substituted butanes listed below, for example. For each compound, sight along the C2-C3 bond and draw Newman projections of the most stable and least stable conformations. Use the data in Table 3.5 to assign strain energy values to each conformation. Which of the eight conformations is most strained Which is least strained ... 

Figure 4.4 The structure of cyclopropane, showing the eclipsing of neighboring C-H bonds that gives rise to torsional strain. Part (b) is a Newman projection along a C-C bond.

Gauche conformation (Section 3.7) The conformation of butane in which the two methyl groups lie 60° apart as viewed in a Newman projection. This conformation has 3.8 kj/mol steric strain. 

Saltikov CW, A Cifuentes, K Venkateswaran, DK Newman (2003) The ars detoxification system is advantageous but not required for As(V) respiration by the genetically tractable Shewanella species strain ANA-3. Appl Environ Microbiol 69 2800-2809. 

Saltikov CW, RA Wildman, DK Newman (2005) Expression dynamics of arsenic respiration and detoxification in Shewanella sp. strain ANA-3. J Bacteriol 187 7390-7396. 

Arsenate 33 Desulfotomaculum auripigmentum Desulfovibrio strain Ben-RA V. atypica Micrococcus aerogene Newman et al. (1997b) Macy et al. (2000) Wolfolk andWhiteley (1962) Wolfolk andWhiteley (1962)... 

Figure 5.102 Tensile stress-strain diagrams for two SMC compounds 25 wt% fiber, bottom, and 65 wt% fiber, top. Reprinted, by permission, from Composite Materials Technology, P. K. Mallick and S. Newman, eds., p. 45. Copyright 1990 by Carl Hanser Verlag.

In addition to angle strain, cyclopropane has a significant amount of torsional strain. This can best be seen by looking at a Newman projection down any of the C—C bonds. As can be seen in this diagram, each C—C bond is held in an eclipsed conformation by the rigidity of the molecule. 

All of the C—C—C bond angles are 109.5°, so this comformation has no angle strain. In addition, it has no torsional strain because all of the C—H bonds are perfectly staggered. This can best be seen by examining a Newman projection down C—C bonds on opposite sides of the ring ... 

Like the chair conformation, all of the C—C—C bond angles of the boat conformation are 109.5°, so it has no angle strain. However, it does have other types of strain. The two red hydrogens, called flagpole hydrogens, approach each other too closely and cause some sceric strain. In addition, the conformations about the green bonds are eclipsed. This can be seen more easily in the Newman projection down these bonds ... 

Draw Newman projections for the anti and gauche conformations about the C—C bond of these compounds. What other factors, besides steric and torsional strain, influence the stability of these conformations ... 

Draw a graph, similar to Figure 3-9, of the torsional strain of 2-methylpropane as it rotates about the bond between Cl and C2. Show the dihedral angle and draw a Newman projection for each staggered and eclipsed conformation. 

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