Bold bonds

FIGURE 1.1 Chemical and stereochemical nature of amino acids. Substituents in (a) and (b) are on opposite sides of the plane N-Ca-C, the bold bond being above the plane. Interchange of any two substituents in (a) changes the configuration. For the Cahn-Ingold-Prelog system of nomenclature, the order of preference NH2 > COOH > R2 relative to H is anticlockwise in (a) = (S) and clockwise in (c) = (R). 

Fig. 4 Lerner s group used phosphonate [3] as the hapten to raise an antibody which was capable of hydrolysing the ester [5] shown alongside it. Schultz found that naturally occurring antibodies using phosphate [4] as their antigen could hydrolyse the corresponding p-nitrophenyl choline carbonate [6]. (Those parts of haptens [3] and [4] required for antibody recognition have been emphasized with bold bonds.)...

Put in wedges and bold bond for perspective if required the lower part of the ring is always at the front... 

Note that the wedges and bold bonds help to show how we are looking at the cyclohexane chair. In practice, particularly to speed up the drawing of structures, we tend to omit these. Then, by convention, the lower bonds... 

By convention, the ring form of sugars is drawn with the ring oxygen to the rear and the anomeric carbon furthest right. Wedges and the bold bond help to... 

Scheme 9.7 The annulene belt is drawn with bold bonds.

Fig. 12 Representation of the seven bonds for which torsion angles of EpoA were defined by tr-CCR NMR [96]. Left stick model of the NMR-derived bioactive conformation. The torsions defined by the tr-CCR measurements are displayed as yellow sticks. Heteroatoms are displayed as spheres O in red, S in yellow, and N in green. Right the same torsions displayed as bold bonds...

Fig. 8-2 Binding of the substrate (NAG-NAM)3 to the active site of lysozyme. The substrate is drawn with bold bonds, the enzyme groups with light-face bonds. H bonds are indicated by dotted lines.

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. 

Conventions for the representation of stereochemistry are also worth noting. A heavy or bold bond indicates that a substituent is pointing toward you, out of the plane of the paper. A hashed bond indicates that a substituent is pointing away from you, behind the plane of the paper. Sometimes a dashed line is used for the same purpose as a hashed line, but the predominant convention is that a dashed line designates a partial bond (as in a transition state), not stereochemistry. A squiggly or wavy line indicates that there is a mixture of both stereochemistries at that stereocenter, i.e., that the substituent is pointing toward you in some fraction of the sample and away from you in the other fraction. A plain line is used when the stereochemistry is unknown or irrelevant. 

The point of attachment is shown by the bold bond at the left of each structure. 

There are many. One of the most confusing is to use a stereochemical bond (ie a hashed or a bold bond) between two stereocentres. For example, amine 33 and alcohol 34 can be drawn without confusion in several ways two of which are shown below. 

The potential confusion arises when we have two stereogenic centres next to one another. The first depiction of aminoalcohol 35 makes perfect sense but the redrawn form is starting to get confusing. Which centre does the bold bond refer to ... 

In fact, we can work out the stereochemistry in the second drawing of 35. If we look at each centre in isolation and consider the bold bond to both then it works. But this is rare and works here because we happen to have syn-35. How we would redraw anti-35 in a similar way Would we use a bold or a hashed bond to do it There is no good answer. The best thing to do is follow these two guidelines—... 

The stereochemical descriptors erythro and threo are used in the following sense. When the aldol is written so that its main chain is in an extended (zig-zag) arrangement, an erythro isomer is one in which the bonds to the a-alkyl group and the 3- yciroxy group both project toward (bold bonds) or away from (dashed bonds) the viewer. 

Allylic strain The destabilization of a molecule, or an individual conformation, by van der Waals repulsion between substituents on a double bond and those in an allylic position [66]. Two types have been identified (see bold bond in figure) Al 2 strain occurs between substituents on an allylic carbon and the adjacent sp2 carbon. A 1 3 strain occurs between substituents on an allylic carbon and the distal sp2 carbon. The latter effect can be quite strong [67]. Originally [66], the terms were defined in the context of cyclohexane derivatives, but more recently the effects have been recognized as important factors in conformational dynamics of acyclic systems [67]. 

Obtained directly from set of bolded bonds in final target product structure found in Part 3. 

FIGURE 9.1 Target bond maps for Nicolaou G5 and Ghosh plans for (-)-platensimycin showing superposition of (i )-carvone and (5)-carvone structures denoted by bolded bonds. 

Figure 2.21 shows the system bond graph, with activity values corresponding to a/b = 1 adjacent to each bond and internal junction structure bonds shown in bold. Bonds 1 and 2 in the figure have relative activities of 0.14 and 2.4% with respect to... 

FIGURE 25.23 Aromatic aryl substrates functionalized by benzene on the presence of [Pd(OAc)J. Numbers in bold are free energy of activation in kilocalories per mole. Bold bonds indicate the experimental observed sites of arylation [34]. Adapted with permission from Ref. [34]. Copyright (2008) American Chemical Society. 

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