Hashed wedge

The plain lines represent bonds that lie in the plane of the paper. The full wedge represents a bond coming out of the paper and the hashed wedge indicates a bond pointing behind the paper. 

The wedges used in structure 4.1 and indeed in all similar homoporphyrin structures in this chapter are used to designate confirmed deviation from macrocyclic planarity at this particular position, and should not be taken as an assignment of absolute stereochemistry. In no case has the separation of homoporphyrin enantiomers been reported. However, racemic epimers that result from substitution at this out-of- plane wcso-like position have in some cases been separated, and solid and hashed wedges are used to designate these epimeric forms as appropriate. 

Let s now examine our problem of comparing a hashed-wedged line formula with a Fischer projection. The actual problem is how to interconvert hashed-wedged line and Fischer formulas. The key to this is recognizing that Fischer projections are pictures of a molecule in an eclipsed conformation. Very important. So the first step in our comparison is to get the hashed-wedged line formula into an eclipsed conformation. Any 60° rotation will do, such as rotation of the left-hand methyl group up out of the page, toward you ... 

Bold and hashed wedges are commonly used in complex molecules, but an additional convention is required. For example, in the representation of paclitaxel (4), ° it cannot be true that all of the bold wedges project toward the viewer to the same plane in space, nor can it be true that all of the dashed wedges project to the same plane behind the page. Rather, each wedge is a local descriptor only, and the sense of depth of the viewer is to be reset at the origin of each wedge. 

The structure shown as the product in the following reaction is incomplete. Complete the drawing with lx)ld or hashed wedges to show all of the relevant stereochemical relationships. 

The first is in conversion of CTs which represent 2-D pictures with chirality indicated by hash/wedge bonds (bond.inout). In these cases, a Z co-ordinate is artifically added, and this representation is turned into a 3-D representation for conversion to local chirality. 

In Summary Determination of organic structures relies on the use of several experimental techniques, including elemental analysis and various forms of spectroscopy. Molecular models are useful aids for the visualization of the spatial arrangements of the atoms in structures. Condensed and bond-line notations are useful shorthand approaches to drawing two-dimensional representations of molecules, whereas hashed-wedged fine formulas provide a means of depicting the atoms and bonds in three dimensions. 

Condensed and bond-line formulas are abbreviated representations of molecules. Hashed-wedged line drawings illustrate molecular structures in three dimensions. 

Convert the following hashed-wedged line formulas into condensed formulas. 

Convert the following condensed formulas into hashed-wedged line structures. 

Draw zigzag hashed-wedged line structures for 2-methylbutane and 2,3-dimethylbutane. 

Figure 2-4 Hashed-wedged line structures of methane through pentane. Note the zigzag arrangement of the principal chain and two terminal hydrogens.

We can use hashed-wedged line structures to depict the three-dimensional arrangement of substituted cycloalkanes. The positions of any remaining hydrogens are not always shown. 

A Fischer (Real Life 5-2) projection is a simphfied way of depicting tetrahedral carbon atoms and their substituents in two dimensions. With this method, the molecule is drawn in the form of a cross, the central carbon being at the point of intersection. The horizontal lines signify bonds directed toward the viewer the vertical lines are pointing away. Hashed-wedged line structures have to be arranged in this way to facilitate their conversion into Fischer projections. 

Conversion of the Hashed-Wedged Line Structures of 2-Bromobutane into Fischer Projections (of the Stereocenter)... 

Notice that just as there are several ways of depicting a molecule in the hashed-wedged line notation, there are several correct Fischer projections of the same stereocenter. 

Conversion of Hashed-Wedged Line Structures into Fischer Projections... 

Draw the hashed-wedged line structures corresponding to Fischer projections A and B, above. Is it possible to transform A into B by means of a rotation about a single bond If so, identify the bond and the degree of rotation required. Use models if necessary. 

Convert the Fischer projections in Exercises 5-15 and 5-16 into hashed-wedged line formulas and determine their absolute configurations by using the procedure described in Section 5-3. When the lowest-priority group is at the top in a Fischer projection, is it in front of the plane of the page or behind it Does this explain why the procedure outlined on p. 183 for determination of configuration from Fischer projections succeeds ... 

A compound that contains two (or, as we shall see, even more than two) stereocenters but is superimposable with its mirror image is a meso compound (mesos, Greek, middle). A characteristic feature of a meso compound is the presence of an internal mirror plane, which divides the molecule such that one half is the mirror image of the other half. For example, in 2,3-dibromobutane, the 2R center is the reflection of the 35 center. This arrangement is best seen in an eclipsed hashed-wedged line structure (Figure 5-11). The presence... 

Figure 6-9 Hashed-wedged line and space-filling drawings of the transition states for 8, 2 reactions of hydroxide ion with (/ chloromethane (B) chloroethane and (C and D) two conibrmers of 1 -chloropropane (C) anti and (D) gauche. Steric interference is illustrated strikingly in the spacefilling drawings. Partial charges have been omitted for clarity. (See Rgure 6-3.)...

Figure 6-10 Hashed-wedged line and space-filling renditions of the transition states for Sn2 reactions of hydroxide ion with (A) 1-chloropropane, (B) 1-chloro-2-methylpropane, and (C) 1-chloro-2,2-dimethylpropane. Increasing steric hindrance from a second gauche interaction reduces the rate of reaction in (B). Sn2 reactivity in (C) is eliminated almost entirely because a methyl group prevents backside attack by the nucleophile in all accessible conformations of the substrate. (See also Figures 6-8 and 6-9.)...

As always with stereochemical problems, it is useful to build models. Draw both molecules and their stereochemistry using the hashed-wedged line notation. Then search for symmetry elements mirror planes and rotational axes. 

Redraw the hashed-wedged line stracture of sugar A (shown in the margin) as a Fischer projection and find ifs common name in Figure 24-1. 

Recall (Section 5-4) that the Fischer projection represents the molecule in an all-eclipsed arrangement. It can be translated into an all-eclipsed hashed-wedged line picture. 

Fischer Projection and Hashed-Wedged Line Structures for D-(-l-)-Glucose... 

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