Wedge-dash structures

Keeping in mind the three-dimensional properties of molecules, Newman projections can be converted to wedged-dashed structures or Fischer projections as desired. It is important to develop facility for manipulating structures and... 

Match each molecular model with the correct line-wedge-dash structure. 

WeTl begin with cis- and ran -l,4-dimethylcyclohexane as represented by wedge-and-dash structural formulas. 

FIGURE 12.5 The structure of methane, as represented by (a) its structural formula, (b) a ball-and-stiek model, (e) a space-filling model, and (d) a wedge-dash projection showing the geometry of the molecule. 

FIGURE 1.25 (a) A wedge-dashed wedge formula for the sigma bonds in ethene and a schematic depiction of the overlapping of adjacent p orbitals that form the tt bond, (b) A calculated structure for ethene. The blue and red colors indicate opposite phase signs in each lobe of the tt molecular orbital. A ball-and-stick model for the o- bonds in ethene can be seen through the mesh that indicates the ir bond. 

Let us use the knowledge about the tetrahedral shape to build structures of other simple alkane molecules. We observe that the consequence of tetrahedral stmcture is the zig-zag form of the alkane chains. Chemical formulas in the following scheme are called wedge-dash formnlas. 

New wedge-dash notation for tetrahedral structures and trigonal pyramidal structures was added. 

The following is a wedge-and-dash structure for the anti-gauche conformation of pentane. Notice that Cl and C4 are anti to each other (when looking down the C2-C3 bond), while C2 and C5 are gauche to each other (when looking down the C3-C4 bond). 

Draw dashed and solid wedge line structures for the trans isomers of chloromethylcyclohexane. 

Methane is a tetrahedral molecule its four hydrogens occupy the corners of a tetra hedron with carbon at its center We often show three dimensionality m structural for mulas by using a solid wedge ) to depict a bond projecting from the paper toward you and a dashed wedge (i 111 ) for one receding away from you A simple line (—)... 

Fischer projection formulas can be used to represent molecules with several stereogenic centers and are commonly used for caibohydrates. For other types of structures, a more common practice is to draw the molecule in an extended conformation witii the main chain horizontal. In this arrangement, each tetrahedral caibon has two additional substituents, one facing out and one in. The orientation is specified widi solid wedged bonds for substituents facing out and with dashed bonds for substituents that point in. 

A note on good practice Dashed and solid wedge-shaped bonds are commonly used when displaying organic structures to convey a sense of the three-dimensional shapes. The dashed wedge-shaped bonds go into the page and the solid wedge-shaped bonds come toward us. The thin lines are in the plane of the paper. 

Whenever we have a structure where the wedges and dashes are implied but not drawn, it is much easier to use this method. There are other examples of carbon skeletons that, by convention, do not show the wedges and dashes. Most of these examples are rigid bicyclic systems. For example. 

Figure 1.19 The structure and bond angles of ethene. The plane of the atoms is perpendicular to the paper. The dashed edge bonds project behind the plane of the paper, and the solid wedge bonds project in front of the paper.

Conjugate acids and bases are related by the gain or loss of one proton. In these structures, a solid wedge is a bond coming out of the plane of the page and a dashed wedge is a bond to an atom behind the page. 

Before we can talk about drawing Newman projections, we need to first review one aspect of drawing bond-line structures that we did not cover in Chapter l. To show how groups are positioned in 3D space, we often use wedges and dashes ... 

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