Structure drawings Newman projection

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 ... 

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

You might prefer to draw the zincNewman projections, as shown in the textbook on p. 863. 

Draw Newman projections of the four stereoisomers of 2-bromo-3-methylpentane in the conformation required for E2 elimination. (See the structures labeled Stereospecificity in the E2 Reaction of 2-Bromo-3-methylpentane on p. 453.) Are the reactive conformations also the most stable conformations Explain. 

Other common methods for representing the three-dimensional structures of molecules include Newman projections for showing conformational relationships and sawhorse figures. Newman projections look down a carbon-carbon bond so that the front carbon, designated by a circle, obscures the carbon directly behind it. Valences (bonds) to the front carbon extend to the center of the circle, while bonds to the rear carbon stop at the circle. Sawhorse projections have the carbon-carbon bond at oblique angles, which attempts to represent a perspective drawing of the molecule. Thus for 2-chloro butane, if one chooses to examine the 2,3 bond, then the sawhorse and Newman projections would be... 

What products are obtained from the reaction between benzaldehyde and butanone in the presence of base (NaH, room temperature) Draw the structural formulae of all of the reaction products in spatially correct Newman projections. Chose the conformation in which the phenyl and carbonyl groups are antiperiplanar to one another. 

Draw the structural formula of 2,2-dichloro-l,l-difluoro-4,4-dimethylcyclo-hexane as a Newman projection formula viewed along the C1-C2 and C5-C4 bonds. Assume that the compound adopts a chair conformation. 

Draw the structure of ( , )-3-chloro-4-fluoro-l,l-dimethylcyclohexane as a Newman projection formula viewed along the C6-C1 and C4-C3 bonds. (The chlorine and fluorine atoms should be drawn antiperiplanar to each other.)... 

Now choose the angle of attack that is the least hindered, and draw a Newman proejetion of the product. Finally, redraw the Newman projection as a normal structure, preferably with the longest chain in the plane of the paper. 

Strategy As in the previous problem, draw the structure, convert it to a Newman projection, and rotate the groups so that the -H and -Br to be eliminated have an anti periplanar relationship. 

Two of the possible conformations of ethane staggered and eclipsed. Interconversion is easy via a 60° rotation about the C—C bond, as shown by the curved arrows. The structures at the left are spacefilling models. In each case, the next structure is a dash-wedge structure, which, if viewed as shown by the eyes, converts to the sawhorse" drawing, or the Newman projection at the right, an end-on view down the C—C axis, in the Newman projection, the circie represents two connected carbon atoms. Bonds on the front carbon go to the center of the circie, and bonds on the rear carbon go oniy to the edge of the circie. 

Draw all possible staggered and eclipsed conformations of l-bromo-2-chloroethane (see the followingball-and-stick model), using Newman projections. Underneath each structure, draw the corresponding dash-wedge and sawhorse structures. Rank the conformations in order of decreasing stability. 

Problem 4.13. Draw Newman and sawhorse projections of 2-methylbutane. Identify eclipsed, staggered, gauche, and antirelationships between sets of methyl groups looking down the C2-C3 bond in your representation of the structure. 

PROBLEM 2.16 Draw the low-energy Newman projection for the structure depicted below by looking down the carbon-carbon bond. 

PROBLEM 3.39 Are the two structures below the same molecule Draw the Newman projection for each looking down the C(2)—C(3) bond. Which form do you think is more stable Why ... 

We must first draw a structural diagram for the molecule and identify the C2—C3 axis and then draw a Newman projection corresponding to a view along the C2—C3 bond. The lowest energy structure is the one that minimizes the repulsions among the substituents. 

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