Dashed bonds

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. 

In these views, the ring is roughly in the plane of the page, a wedged bond protrudes out of the page, and a dashed bond recedes into the page. Two substituents are cis if they are both out of or both into the page, and they are trans if one is out of and one is into. 

In some cases, particularly where additional rings are present, structural formulae can be clarified by use of the Mills depiction. Here the main hemiacetal ring is drawn in the plane of the paper dashed bonds denote substituents below this plane, and thickened bonds those above. 

Addition takes place through the initial formation of a n complex, which changes into a cyclic four-center transition state with the boron atom adding to the less hindered carbon atom. The dashed bonds in the transition state represent bonds... 

Fig. 7 The novel packing motif of a" -(BEDT-TTF)4([Fe(C5H4S03)2]-6H20. Regions containing a-type circled with a dotted line, while regions with P"-packing are highlighted with an oval (top). The anionic layer is characterized by an extensive hydrogen bonding network (dashed bonds) between water molecules and the sulfonate functionality of the anion...

To name the reaction, draw a dashed line where the new bond is made, draw a squiggly line across the bond that is broken, and count the number of atoms from the termini of the dashed bond to the termini of the squiggly bond. 

FIGURE 3-3 Stereoisomerism in n-amino acids, (a) The two stereoisomers of alanine, l- and o-alanine, are nonsuperimposable mirror images of each other (enantiomers), (b, c) Two different conventions for showing the configurations in space of stereoisomers. In perspective formulas (b) the solid wedge-shaped bonds project out of the plane of the paper, the dashed bonds behind it. In projection formulas (c) the horizontal bonds are assumed to project out of the plane of the paper, the vertical bonds behind. However, projection formulas are often used casually and are not always intended to portray a specific stereochemical configuration. 

FIGURE 16-10 Iron-sulfur center in aconitase. The iron-sulfur center is in red, the citrate molecule in blue. Three Cys residues of the enzyme bind three iron atoms the fourth iron is bound to one of the carboxyl groups of citrate and also interacts noncovalently with a hydroxyl group of citrate (dashed bond). A basic residue ( B) on the enzyme helps to position the citrate in the active site. The iron-sulfur center acts in both substrate binding and catalysis. The general properties of iron-sulfur proteins are discussed in Chapter 19 (see Fig. 19-5). 

Dashed bond goes behind the plane of the page. 

Nonmetal atoms share electrons until each has completed its octet (or duplet) a Lewis structure shows the arrangement of electrons as dashes (bonding pairs) and dots (lone pairs). 

More recently a new method for designating the stereochemical relationship of diastereomers has been developed. In this method the carbon backbone is extended in the plane of the paper, blackboard, or computer screen in the horizontal direction. Groups will extend from this backbone either in front of the plane or behind it and are designated by bold or dashed bonds, respectively. If two substituents extend in the same direction, their spatial relationship is designated syn if they extend in opposite directions, their spatial relationship is designated anti. 

Shown are the two different coiling patterns of famesol that might give the carbon skeleton of santonin. Points where the carbon skeleton of famesol are cross-linked are shown by dashed bonds. 

Dash formula diagram all atoms, bonds as dashes Bond line formula hide H, show carbon skeleton as... 

Draw in three dimensions, with solid, wedged, and dashed bonds, the tetrahedral bonding around sp3-hybridized carbon atoms. 

Figure 5.5.8-2 The proposed chromophores of animal vision, the Rhodonines, based on Vitamin Al. Retinol (Vitamin A1) is shown for reference. Each chromophore is shown in its ionic form. The oxygen atoms are shown in red. The conjugation critical to absorption in the visual region of the spectrum is shown by the dashed bond. The horizontal line below each molecule shows the relative length of its resonant structure.

Reaction scheme 26 illustrates the chemisorption pathway in which, after a precursor state, first a hy-peroxo species and then a peroxo species is formed. The dashed bonds indicate incomplete charge transfer. Only at the final step of dissociation of the molecular... 

Now notice that the transition state is drawn in square brackets and marked. Note the long dashed bonds not yet completely formed or not yet completely broken and the partial charges (+) and (-) meaning something about half a charge (the products have complete charges shown in circles). 

Remember that the bold wedges raprasentbondscorhlngtowardeyou, out of the paper, and the dashed bonds represent bonds going sway fromyoif, into the paper. 

When we don t show bold and dashed bonds to indicate the three-dimensional structure of the molecule, we mean that we are talking about both enantiomers of the molecule. Another useful way of representing this is with wiggly bonds. Wiggly bonds are in fact slightly ambiguous chemists use them to mean, as they do here, both stereoisomers, but also to mean just one stereoisomer, but unknown stereochemistry. 

The dashed bonds indicate partial bonds (the C—Nu bond is partly formed and the C—X bond partly broken) and the charges in brackets indicate substantial partial charges (about half a minus charge each in this case as they must add up to one ). Transition states are often shown in square brackets and marked with the symbol t- Another way to look at this situation is to consider the orbitals. The nucleophile must have lone-pair electrons, which will interact with the a orbital of the C-X bond. 

Figure 44 Crystal structures (a) [Pt(NCN-OH)Cl] XLIV [44a] and (b) [Pt(S02) (NCN-OH)Cl] XLV [129a,b] (NCN = tridentate pincer ligand C6H2-5-(OH)-2, 4-(CH2NMe2)2 ). O-H Cl hydrogen-bonded chains are maintained upon uptake of S02. Hydroxyl group, chloride ligand and SOi ligand are shaded. Hydrogen bond network and Cl S donor-acceptor interactions are shown as dashed bonds.

Bond information includes the bond order, that is, single, double, or triple bond, and bond style, such as simple straight-line bond, wedged bond, dashed bond, wavy bond, broken-line bond, bold bond, and so on. Bond information can also include some special bond types representing the aromatic bonds or bond stereochemistry, for example, wedged or dashed bond. Bond labels are also sometimes found in structures. Different types of bond information are illustrated in Figure 4.2. 

FIGURE 4.14 Example on joining between atoms and bonds intheCLiDE system. Although the atom label OAc is closer to the two solid bonds (b and c) than to the dashed bond (a), OAc is correctly joined to bond a. 

Strategy Two substituents are cis if they both have either dashed or wedged bonds. The substituents are trans if one has a wedged bond and the other has a dashed bond. 

Wedge and dashed bonds are used as sparingly as possible to avoid confusion. The majority of tetrahedral centres require only one such bond to imply the stereochemistry of the centre. 

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