Newman projection molecular model

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... 

Figure 3.6 A sawhorse representation and a Newman projection of ethane. The sawhorse representation views the molecule from an oblique angle, while the Newman projection views the molecule end-on. Note that the molecular model of the Newman projection appears at first to have six atoms attached to a single carbon. Actually, the front carbon, with three attached green atoms, is directly in front of the rear carbon, with three attached red atoms.

Newman, Melvin S., 93 Newman projection, 93 molecular model of, 93 Nicotinamide adenine dinucleotide, biological oxidations with, 625-626 reactions of, 725 structure of, 725, 1044 Nicotinamide adenine dinucleotide (reduced), biological reductions with, 610-611... 

Newman projections, looking along the central C2—C3 bond, for four conformations of butane. Construct butane with your molecular models, and sight down the C2—C3 bond. Notice that we have defined the dihedral angle d as the angle between the two end methyl groups. 

The two chair conformations of methylcyclohexane interconvert at room temperature, so the one that is lower in energy predominates. Careful measurements have shown that the chair with the methyl group in an equatorial position is the most stable conformation. It is about 7.6 kJ/mol (1.8 kcal/mol) lower in energy than the conformation with the methyl group in an axial position. Both of these chair conformations are lower in energy than any boat conformation. We can show how the 7.6 kJ energy difference between the axial and equatorial positions arises by examining molecular models and Newman projections of the two conformations. First, make a model of methylcyclohexane and use it to follow this discussion. 

The conformation of cyclobutane. Part (a) shows computer-generated molecular models. Part (c) is a Newman projection along the C1-C2 bond, showing that neighboring C-H bonds are not quite eclipsed. 

The boat conformation of cyclohexane (18) can be constructed from a molecular model of the chair form by holding the right-hand three carbons C(2), C(3) and C(4) of 15, clamped from the top with the hand and moving the left-hand three carbons upward. A Newman projection of the boat form looking along the C(l)-C(2) bond, and shown in 19, is reminiscent of the highest energy cis conformation of butane. 

Let us now consider which bonding model is more amenable to qualitative predictions of molecular conformation. Specifically, what should be the preferred conformation of propene Walters noted that two conformers of propene (designated as I and II) can be visualized as Newman projections observed by sighting down the C3-C2 bond (Figiue 1.33). In conformer I, a C-H bond eclipses a carbon-carbon double bond, hi conformer II, a C-H bond eclipses a C—H bond. Assuming that there is greater electron density in a double bond than in a C-H single bond, we would expect conformer II to be more stable. Experimentally, however, conformer I was found to be more stable by about 2 kcal/mol. 

Learn to draw Newman projections and sawhorse formulas. Build handheld molecular models and compare them with your drawings. 

Which of the following two conformations is the more stable Hint Use molecular models or draw Newman projections looking down the bond being... 

One conformation appears to be lowest in energy. This conformation is shown as molecular model 48D in the same Newman-type projection as 48C. This conformation is thought to look a little like an easy chair, and it is called a chair conformation. The chair shape can be seen in 48B or in molecrdar model 48E, which views the conformation from the side. Note that 48D is the molecular model of48B, and that 48D and 48E are identical, but simply viewed from a different perspective. 

Molecular models and Newman projections of the staggered and eclipsed conformations of ethane. The dihedral angle in the staggered form is 60T and that in the eclipsed form is 0°. The C—C bond is rotated slightly in the Newman projection of the eclipsed form in order to show the H atoms attached to the back C atom. 

The molecular model of S20 F2, the characterization of the angles of rotation, and the Newman projections of the conformer established by Hencher and Bauer (1973)... 

The molecular models and Newman projections of two conformers of fluorosulphuric acid methyl ester and chlorosulphuric acid methyl ester... 

Newman projection of the molecular models of methane sulphonyl fluoride, methane sulphonyl chloride, and dimethyl sulphone representing view along the S-C bond... 

Building a molecular model will help you visualize many of the concepts being discussed in this section. Build a model of cyclohexane to convince yourself that the same Newman projection is obtained when the molecule is viewed along the other two pairs of parallel C —C bonds. 

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