Arrows atom-specific

The second arrow we have seen before. Here again you could use an atom-specific arrow to make it clear that the electrons in the c bond act as a nucleophile through the hydrogen and not through the boron atom. 

Lich reaction simply involves the nucleophilic attack of the organometallic reagent on the aldehyde rr ketone followed by protonation. You may draw the intermediate as an anion or with an O-metal ->nd as you please. Note the atom-specific arrows to show which atom is nucleophilic. In the second example the allyl-lithium might attack through its other end. 

Most nuclear reactions involve the breaking apart of the nucleus into two or more different elements or subatomic particles. If we know all but one of the particles, then the unknown particle can be determined by balancing the nuclear equation. When chemical equations are balanced, we add coefficients to ensure that there are the same number of each type of atom on both the left and right of the reaction arrow. However, in order to balance nuclear equations we ensure that there is the same sum of both mass numbers and atomic numbers on the left and right of the reaction arrow. Recall that we can represent a specific isotope of an element by the following symbolization ... 

In Figure 4.2 we have drawn how we can distinguish the two faces of an alkene, or rather the side of attack of a specific atom of the alkene. The arrow on the left approaches the lower carbon of the alkene and when looking from this viewpoint we count the weight of the three substituents the same way as in the CIP rules. We then see the order 1, 2, and 3 counter-clockwise, and we say that the arrow approaches the carbon atom from the si face. For simplicity we call this the si face of the alkene and in most cases this will do. If all four substituents at the alkene are different we can determine the re/si properties of both carbon atoms and these may be different This results in the nomenclature that an alkene may have a re,re and si,si face or re,si and si,re face. Thus, in the latter case one has to indicate to which atom the label is referring. For any enantiospecific, catalytic reaction (hydrogenation, hydroformylation, polymerisation) it is very convenient to use the re and si indicators in the discussion. 

Figure 1.12 Representation of structural formulas with lines. A carbon atom is understood to be at each corner and at the end of each line. The numbers of hydrogen atoms attached to carbons at several specific locations are shown with arrows.

Figure 1. Compilation of platinum mass activities as a function of platinum B.E.T. surface area [ ] Watanabe et alJ [0] Buchanan et al.s [ ] Buchanan et al. and [0] Bregoli6. The solid line is 0.6A.m 2 constant specific activity platinum. The broad arrow on the abscissa denotes the maximum surface area for a platinum crystallite when all of the atoms are located at the surface (275 m2 g 1 Pt). Phosphoric acid at 190 °C and 0.9 V vs. hydrogen in the same electrolyte, (a) Data up 210 m2g" Pt. (b) Data below 100m2g Pt m Bregoli6 results on unsupported platinum black.

Fig. 16 Electron transfers per bonds introduced in the modelization of an SrTi03(001) surface (left pannel) and of an MgO(lll) surface (right pannel). On SrTi03(001), specific transfers A(p q and Agj o (represented by thick arrows) are introduced inside the surface layer and in between the surface and sub-surface layers for Ti-0 bonds and Sr-0 bonds involving surface atoms. On MgO(lll), only the first inter-plane transfer is assumed to be modified, (from Ref. 4).

FIGURE 5.15 The ground-state electron configurations of first- and second-period atoms. Each horizontal line represents a specific atomic orbital. Arrows pointing up represent electrons with spin quantum number m, = +j and arrows pointing down represent electrons with spin quantum number m, = -j. 

ChemLit has facilities for input of chemical reactions. A reaction is indicated by a reaction arrow, the composite placed in the GROUP option between two structures. The user may mark the atoms that actually participate in reaction. Later searches can be made for the flagged atoms to retrieve specific reactions. 

AB olefinic compound ABO carbonyl compound OR = 0-ring compound R, AB contain smaller number of carbon atoms than R. Reactions for specific compounds are indicated by attaching an appropriate letter. Broken arrows in reactions (SA), (SB), and (SQ indicate overall processes. 

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