Wedge bond

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 6.48 Trigonal bipyramidal PF5, showing Berry pseudorotation. The apical bonds are solid lines, the equatorial bonds wedges. Fluorine atoms are numbered, but if they were not, the pseudorotation would be equivalent to rotation through 90° about the C-F5 bond ( pivot of the pseudorotation).

Fig. 15.4 Crack propagation in epoxy-bonded wedge specimen treated with 2 wt.% AD-102.

The asymptotic stress state near the apex of dissimilar bonded wedges (i.e. interface comer) for plane stress or strain, when the wedge materials are isotropic and linear elastic, has the form... 

In a Fischer projection, assume horizontal bonds = wedge bonds vertical bonds = dash bonds... 

Nanotubes from Hydrogen Bonded Wedge- or Sector-like Molecules... 

The stereochemistry is usually expressed in structure diagrams by wedged and hashed bonds. A wedge indicates that the substituent is in ont of a reference plane and a hashed bond indicates that the substituent is pointing away om the viewer (behind the reference plane). This projection is applied both to tetrahe-... 

A molecule editor can draw a chemical structure and save it, for example as a Molfile. Although it is possible to include stereochemical properties in the drawing as wedges and hashed bonds, or even to assign a stereocenter/stereogroup with its identifiers R/S or E/Z), the connection table of the Molfile only represents the constitution (topology) of the molecule. 

Similarly the stereobonds" can be defined and added to the bond list in the fourth column of the CT. A single bond acquires the value of 0 if it is not a "stereobond, 1 for np (a wedged bond). 4 for either up or down, and 6 for down (a basbed bond), The cisjtrans or E[Z configuration of a double bond is determined by the x,y.2 coordinates of the atom block if the value is 0, Tf it is 3, the double bond is either cis or tmns. In the bond block of our example (Figure 2-76), the stereocenter is set to 1 (up) at atom 6 (row 6, column 4 in the bond block), whereas the configurations of the double bonds are determined by the x,y coordinates of the atom block. 

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 (—)... 

Lei s relurn fo bromochlorofluoromelhane as a simple example of a chiral mole cule The Iwo enanliomers of BrClFCH are shown as ball and slick models as wedge and dash drawings and as Fischer projections m Figure 7 6 Fischer projeclions are always generated Ihe same way Ihe molecule is oriented so lhal Ihe verlical bonds al Ihe chiralily center are directed away from you and Ihe horizonlal bonds poinl toward you A projeclion of Ihe bonds onto Ihe page is a cross The chiralily center lies al Ihe center of Ihe cross bul is nol explicilly shown... 

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. 

Another means of providing a hydration-resistant surfaee is its treatment with a hydration inhibitor [41]. Fig. 9 shows wedge tests results for a Forest Produet Laboratory (FPL) bond [43], an FPL bond pretreated with nitrilotrismethylenephos-phonie (NTMP) aeid [42,44,45], and a PAA bond. The monolayer eoverage of NTMP stabilizes the FPL surfaee against hydration and provides wedge test bond performanee similar to that of PAA-treated adherends. 

Because of their greater thickness, CAA oxides serve to protect the metal surface from corrosion better than thinner oxides but the important factor for bond durability is the stability of the outer oxide structure when water diffuses to the oxide-polymer interphase. Accordingly, it would be expected that the performance of CAA treated adherends would be similar, although no better, than that of PAA, or BSAA. The wedge test data shown in Fig. 20 and other work [29,77,97,98] support this and demonstrate that when these processes are done correctly the wedge test crack will be forced to propagate entirely within the adhesive. Similar arguments are likely with BSAA adherends, also. 

Fig. 20. Wedge test results showing PAA, CAA, and BSAA treated aluminum bonds. (Note that this test involved thicker adherends than is typical and therefore crack lengths cannot be compared to those of other tests.)...

Sol-gel film.s deposited on a grit-blasted aluminum surface give performance close to PAA bonds (Fig. 22) with generally cohesive failures observed in wedge tests. Given that one application of this treatment is repair, the performance is... 

Occasional in-service delaminations occurred at the aft tip of the wedge. Because there was no metal-to-metal closeout bond at the aft tip, any slight incidental damage could easily crack the bond slightly and allow moisture to enter the core. Eventually, freeze-thaw damage and delamination would occur. 

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