Potential energy diagram for rotation about

FIGURE 3 4 Potential energy diagram for rotation about the carbon-carbon bond in ethane Two of the hydrogens are shown in red and four in green so as to indicate more clearly the bond rotation... 

Fig. 3.3. Potential energy diagram for rotation about C(2)—C(3) bond of n-butane.

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. 

Sketch an approximate potential energy diagram for rotation about the carbon-carbon bond in 2,2-dimethylpropane similar to that shown in Figures 3.4 and 3.7. Does the form of the potential energy curve of 2,2-dimethylpropane more closely resemble that of ethane or that of butane ... 

Figure 4.7. A sketch of a potential energy diagram for rotation about the carbon-carbon single bond in ethane (CH3CH3). The staggered form with an H-H dihedral angle of 60° is about 2.9kcalmoT more stable than the eclipsed form with an H-H dihedral angle of 0°.

Vq can be taken as being equal to the ethane barrier (2.S-2.9 kcal/mol). The potential energy diagram for rotation about the C-C bond of ethane is given in Fig. 3.1. The ethane barrier may be taken as a standard rotational barrier for acyclic hydrocarbons when analyzing the contribution of torsional strain to the total steric strain. The stereoelectronic origin of the ethane barrier was discussed in Chapter 1. Any steric interactions which are present in more highly substituted systems will make an additional contribution to the barrier." ... 

E>raw a qualitative potential-energy diagram for rotation about the C3-C4 bond in 2-methylpentane. Show Newman projections for all conformations located at the maximum and minimum points on your graph. Describe similarities and differences with other molecules discussed in this section. 

PRACTICE EXAMPLE B Sketch a potential energy diagram for rotation about the Cl —C2 axis in 1-chloropropane. 

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