Projection formulas Newman

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

In Newman projection formulas (the two figures on the right) the observer looks at the C C bond head on. The three lines emanating from the center of the circle represent the bonds coming from the front carbon, with respect to the observer. 

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

A Newman projection formula shows that the P-hydrogen and the chlorine are anti periplanar when they are both axial. 

Fig. 11.— Newman Projection-Formulas, Viewed Along the C-4-C-5 Bond in a, Compound 86, and b, Compound 87 (from Ref. 100, with permission).

Writing the above (a) and (b) forms in Newman projection formula, the picture will be as follows ... 

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-... 

Figure 1.10 Definitions of the torsional angles fa ip, and w. These are all equal to 180° for a fully extended polypeptide chain (top left). to, defines rotation about the C,—Nl+1 bond. The normal tram planar peptide bond has = i/r = 180°, bottom) left, fa viewed along N —C bond (N >C) right, fa viewed along the C —C(C , — C j).

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

Convert the Fischer projection formula for a tetrose to a sawhorse or Newman projection formula, and vice versa. 

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.)... 

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. 

Fig. 17 Newman projection formulas for staggered and eclipsed rotamers.

Fig. 10 The postulated reaction mechanisms for bond cleavage in the respective intermediates 38 (a, b) and 39 (d) of 14-OH and 14-H-morphinan, with their Newman projection formulas (c, e). In intermediate 38, the CPM-N17 bond appears to be nearly orthogonal to the 7i-orbital (green) of the carbonyl group (a, c). However, the C16-N17 bond appears to be parallel to the 7t-orbital (green) (b, c). The CPM-N17 bond in intermediate 39 could be parallel to the 7i-orbital (green) (d, e)...

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.

Dithiolanes can be viewed as cyclic disulfanes. A C-S-S-C dihedral angle of 26.6° results from the elctronic interaction between the S-atoms. For this reason, a considerable ring strain is caused by the widening of the bond angles, as can be deduced from the Newman projection formula. The strain enthalpy was found to be 67 kJ mol-i. 

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