Projection Newman

In this projection the reader looks along a single bond, so as to discern clearly the orientation of the substituents connected to the atoms that form that single bond. There are two situations in which 

It is used in particular to determine on which side an incoming nucleophile will attack a carbonyl group. Cram s rule states that the side of attack is the one that offers less steric hindrance. This allows the stereochemistry of the product to be predicted. 

L Small, medium and large groups attached to a-carbon 

---

Newman projections were devised by Professor Melvin S Newman of Ohio State University... 

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... 

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... 

We can view this reaction as the replacement of one or the other of the two methylene protons at C 2 of butane These protons are prochiral atoms and as the red and blue protons m the Newman projection indicate occupy mirror image environments... 

Newman projection (Section 3 1) Method for depicting con formations in which one sights down a carbon-carbon bond and represents the front carbon by a point and the back carbon by a circle... 

Acyclic Compounds. Different conformations of acyclic compounds are best viewed by construction of ball-and-stick molecules or by use of Newman projections (see Fig. 1.2). Both types of representations are shown for ethane. Atoms or groups that are attached at opposite ends of a single bond should be viewed along the bond axis. If two atoms or groups attached at opposite ends of the bond appear one directly behind the other, these atoms or groups are described as eclipsed. That portion of the molecule is described as being in the eclipsed conformation. If not eclipsed, the atoms... 

FIGURE 1.2 Newman projections for ethane, (a) Staggered (b) eclipsed. 

Vicinal CH coupling constants Hqh resemble vicinal HH coupling constants in the way that they depend on the cosine of the dihedral angle 9 between the CC bond to the coupled C atom and the C//bond to the coupled proton (cf Fig. 2.16), as illustrated by the Newman projections of the conformers 20a-c of a propane fragment. 

Substituent effects calculated for structure B lead to values which are not perfect but which agree more closely than for A with the measured C shifts of the benzene ring carbon atoms. The dia-stereotopism of the NC//2 protons in the H NMR spectrum also points to B as the Newman projection C along the C/fj-ammonium-N bond shows ... 

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. 

Higher alkanes having unbranched carbon chains are, like butane, most stable in theh all-anti conformations. The energy difference between gauche and anti conformations is similar- to that of butane, and appreciable quantities of the gauche conformation are present in liquid alkanes at 25°C. In depicting the conformations of higher alkanes it is often more helpful to look at them from the side rather than end-on as in a Newman projection. Viewed from this perspective, the most stable conformations of pentane and hexane... 

The dihedrals for the remaining two hydrogens are best visualized with a Newman projection. They are located above and below the plane of the C-C-C bond. H5 is the hydrogen below the plane, and its dihedral is 60°. The dihedral for H6 could be expressed as either 300° or -60° we ll use the latter to express the symmetry of the molecule. Here are the Z-matrix lines for these atoms ... 

Newman projections are helpful in determining the proper dihedral angles for the fluorines and hydrogens. Here are diagrams for the RR isomer, looking down the C-C bond in both directions ... 

A similar process, using the Newman projection diagram on the right, which places C2 in front of Cj, and uses Clj as the third atom for the dihedral angles, results in the last two lines of the Z-matrix ... 

NBO population analysis 195 NBO program 196 Newman projections 290, 292 NewZMat utility xxxvii Windows xlvi nice command xxxviii nitrobenzene 165 NMR properties 21,29, 53, 104 Nobes 117 Norden 218 normal modes 65 normal termination message xlv nuclear displacements 65 numeric second derivatives 61 Nusair 119... 

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 ... 

---