Drawing Newman Projections

Among the various ways in which the staggered and eclipsed forms are portrayed, wedge-and-dash, sawhorse, and Newman projection drawings are especially useful. These are shown for the staggered conformation of ethane in Figure 3.2 and for the eclipsed conformation in Figure 3.3. 

In each case, draw the compound, determine what three groups are on each of the carbons to be placed in the Newman projection, draw the Newman projection with the bonds for the front carbon emanating from the center of the circle and those of the back carbon coming from the perimeter, and put the three groups on each carbon. Rotate between staggered and eclipsed conformations to get the extreme forms. 

Using Newman projections, draw the most stable conformer for the following ... 

The Newman projection. Drawing and seeing Newman projections is a critical skill in organic chemistry. 

Using Newman projections, draw each of the following molecules in its most stable conformation with respect to the bond indicated (a) 2-methylbutane, C2-C3 bond (b) 2,2-dimethyl-butane, C2-C3 bond (c) 2,2-dimethylpentane, C3-C4 bond (d) 2,2,4-trimethylpentane, C3-C4 bond. 

Sight down the C 2—C 3 bond and draw Newman projection formulas for the... 

The stereoselectivity of elimination of 5 bromononane on treatment with potassium ethox ide was described in Section 5 14 Draw Newman projections or make molecular models of 5 bromononane showing the conformations that lead to cis 4 nonene and trans 4 nonene respec tively Identify the proton that is lost in each case and suggest a mechanistic explanation for the observed stereoselectivity... 

Internal rotation in isooctane (2,2,4-trimethylpentane) creates a large number of staggered conformations. However, only rotation about the C3-C4 bond produces conformations with different structures. Plot the energy of isooctane (vertical axis) vs. HCCCtBu torsion angle, i.e., about the C3-C4 bond (horizontal axis). How many minimum energy structures are there Are they all fully staggered Draw Newman projections that show the conformation of these structures. How does steric repulsion affect isooctane conformation ... 

Sighting along the C1-C2 bond of 1-clUoropropane, draw Newman projections of the most stable and least stable conformations. 

I Sight along the C2-C3 bond of 2,3-dimethylbutane, and draw a Newman projection of the most stable conformation. 

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 ... 

What stereochemistry do you expect for the alkene obtained by E2 elimination of, (lR /O-LZ-dibromo-l -diphenylethane Draw a Newman projection of the reacting conformation. 

There are two very important drawing styles that show conformations and give us the power to predict what conformations are available to different types of molecules Newman projections and chair conformations ... 

Before we can talk about drawing Newman projections, we need to first review one aspect of drawing bond-line stractures that we did not cover in Chapter 1. To show how groups are positioned in 3D space, we often use wedges and dashes ... 

Now we place the three groups that are on the back carbon atom into our drawing. There is one methyl group and two hydrogen atoms. If we put them into our drawing, then we get our Newman projection. It looks like this ... 

It is important that you can see what this drawing represents, because we cannot move forward until you see it very clearly. We are essentially looking at a carbon-carbon bond, focusing on the three groups attached to each carbon atom. The central point in our Newman projection (where the lines to the Cl, F, and Me meet each other) is the first carbon. The big circle in the back is our back carbon. All at once... 

EXERCISE 6.1 Draw a Newman projection of the following compound looking from the perspective of the arrow ... 

PROBLEMS Draw Newman projections for each of the following compounds. In each case the skeleton of the Newman projection is drawn for you. You just need to fill in the six groups in their proper places. 

We have seen that Newman projections are a powerfnl way to show the different conformations of a molecule. We mentioned earlier that there are staggered conformations and eclipsed conformations. In fact, there are three staggered and three eclipsed conformations. Let s draw all three staggered conformations of butane. The best way to do this is to keep the back carbon atom motionless (so the fan in the back is not spinning), and let s slowly turn the groups in the front (only the front fan is spinning) ... 

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