Conformations Newman projection formulas

Figure 4.5 a) The staggered conformation of ethane, b) The Newman projection formula for the staggered conformation. 

See Fig. 9-3. The circle represents the C s of any given ring C—C bond. The other C s of the ring bridge these two C s, one to the front C (heavy line) and the other to the back C (ordinary line). This Newman projection formula reveals that the H s on adjacent C s are skewed in the puckered conformation. 

In the transition state of the enantio-determining cyclometalation step, F - G, the Rh, nitrogen, C(l), and one of the hydrogens would be roughly coplanar, which requires either clockwise or counterclockwise rotation about the N—C(l) axis (see the Newman projection formula F in Scheme 16). The transition state models la and lb explain the prevailing clockwise rotation of the conformer Fa with respect to the coun-... 

Draw, using dash-wedge, sawhorse, or Newman projection formulas, the important conformations of ethane, propane, butane, and various halogenated derivatives of these alkanes. 

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. 

The stereodescriptor erythro indicates that the chlorine atom and the hydroxy group lie on the same side of the main chain in a Fischer projection formula. Since it does not define an absolute configuration, two enantiomers must be considered. The Fischer projection formula, which represents an eclipsed conformation, is simplest first converted into a sawhorse projection (also in its eclipsed conformation) and then one side of the molecule rotated until both the reference groups, the chlorine atom and the hydroxy group, adopt an antiperiplanar arrangement. The required Newman projection formula can then be derived from these formulae. 

Figure 19.14 Panel A shows dopamine, 13 from prior Scheme 19.7, in its extended or (E) conformation, which allows for a staggered anti-Newman Projection formula (Ar = 3,4-dihydroxyphenyl). Panel B shows 13 in its folded or (F) conformation, which leads to a fully eclipsed Newman Projection formula of higher energy. Panel C shows ADTN 29, THiQ 30 and apomor-phine 31. d1, d2, d1 and d2 (in the far-right column) refer to distances between the partners for groups (a), (b), and (c) that would exist on the dopamine receptor in order to accommodate dopamine s E or F conformation, respectively. The different spatial arrangements for these two sets of partnering groups are apparent.

Acetylcholine is a neurotransmitter in the central nervous system in humans. Sighting down the C-1 to C-2 bond, complete the Newman projection formulas for the anti and gauche conformations of acetylcholine. 

When we do conformational analysis, we will find that certain types of structural formulas are especially convenient to use. One of these types is called a Newman projection formula and another type is a sawhorse formula. Sawhorse formulas are much like dash-wedge three-dimensional formulas we have used so far. In conformational analyses, we will make... 

In Figs. 4.5a,b we show ball-and-stick models and a Newman projection formula for the staggered conformation of ethane. The st gered conformation of a molecule is that conformation where the dihedral angle between the bonds at each of the carbon-carbon bonds is 180° and where atoms or groups bonded to carbons at each end of a carbon-carbon bond are as far apart as possible. The 180° dihedral angle in the sta ered conformation of ethane is indicated in Fig. 4.5h. 

Use Newman projection formulas for ethylene glycol (1,2-ethanediol) and butane to explain why the gauche conformer of ethylene glycol is expected to contribute more to its ensemble of conformers than would the gauche conformer of butane to its respective set of conformers. 

Staggered conformation (Section 4.8A) A temporary orientation of groups around two atoms joined by a single bond such that the bonds of the back atom exactly bisect the angles formed by the bonds of the front atom when shown in a Newman projection formula ... 

In case the groups R or Z in VIII are chiral, the double bond plane gets diastereotopic and the approaches of Y from one and the other side of the bond become inequivalent (asymmetrical induction)—the choice of the approach will depend on the conformation of R. For the reactions of nucleophilic addition to alkenes and carbonyl compounds the sterical models represented by the Newman projection formulas XVII are usually invoked for the rationalization of stereoselectivities ... 

Figure 4.5 (a) The eclipsed conformation of ethane. ffajThe Newman projection formula for the eclipsed conformation. 

The sawhorse or Newman representations of 2-butanol, 5a and 5b and 6a and 6b, are excellent for showing the arrangements of the atoms in conformations, but are needlessly complex for representing the stereochemical configuration. Fischer projection formulas are widely used to show configurations and are quite straightforward, once one gets the idea of what they represent. 

The Newman representation 25a or 26a of meso-tartaric acid does not have a mirror plane. Why is it different from the Fischer projections in this respect The reason is that the projection formulas represent a particular eclipsed conformation 27 of tartaric acid that does have a mirror plane ... 

This is a problem similar to 5-29, except that the structures are written mostly as projection formulas of the Fischer or Newman type. Determine the relationship between the pairs of compounds as one of the following identical, position isomers, enantiomers, diastereomers, conformational isomers, or cis-trans isomers. (D stands for deuterium, the hydrogen isotope of mass 2.)... 

If you view the second formula from the top, you will see that it is just a three-dimensional representation of the Fischer projection. Horizontal groups at each stereogenic center come up toward you, and vertical groups recede away from you. The second formula represents an eclipsed conformation of D-threose. The third and fourth formulas represent sawhorse and Newman projections, respectively, of a staggered conformation of D-threose. 

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. 

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