Problem spaces

In addition, many other aspects must be considered when developing a catalytic reaction for industrial use these include catalyst separation, stability and poisoning, handling problems, space-time yield, process sensitivity and robustness, toxicity of metals and reagent, and safety aspects, as well as the need for high-pressure equipment. 

Those who read this chapter may share with its authors the feelings expressed in Ref. 110 The dynamics in this particular problem space seems to have been rather more diffusive than ballistic. It is therefore wise to have some idea of where the ultimate destination is and to be familiar with the strategies that are most likely to take us there. 

I have argued in the past that I thought there were salary inequities, but I was only given summaries of data that did not address the problem. Space is pretty clear—we have a small department and I can go measure it myself. Our chair recognizes that this (space distribution) generally has been public information. 

Approach of Text Problem Spaces Tree Searches Control Knowledge Overview the Principle of Electron Flow Nucleophiles Electrophiles... 

If you were planning a road trip across the US, you would need a map of the highways. It would allow you to see all routes from your starting city to your goal city. You would then choose the best route for what you wanted to see and the time you had for the trip. This is exactly the process you want to go through for understanding organic chemistry. We need a map and the ability to choose the best route. Our maps of problems are called problem spaces and are often shown as trees, with a decision to be made at each branch point. 

Figure 1.1 A generic problem space and some strategies for tree searches in the problem space.

Since just a few mechanistic reaction types form the core of an organic course, we strive to understand these important reaction archetypes. What does the problem space for each archetype look like, and how do the reactant structure and reaction conditions influence the most favored route ... 

Before we explore the problem space for a simple proton transfer reaction, we need to understand the basics of bonding and define a consistent nomenclature. In order to use the electron flow paths, you first need to be able to keep track of atoms and electrons— write Lewis structures correctly and easily. 

This text will use energy surfaces as problem space maps, and also will use the related energy diagrams to explain why a particular reaction may be favorable and how factors influence that favorability. We need to understand why and if a process is energetically downhill to predict whether it has a chance of happening. 

Problem Space for Mechanisms Make Conscious Decisions Mapping Changes Pruning the Tree—Crosschecks Exampie Proton Transfer Mechanism... 

The set of all possible steps that could occur in a problem is its problem space. It includes incorrect, partially correct, and correct routes. Our search for an answer occurs within this problem space. Often instructors present just the one correct route, leaving you to wonder whether your different route is OK or not. At this stage, we are concerned with a reasonable mechanism, not necessarily the absolute best. The problem space is often in the shape of a tree, with branches occurring at each decision point. We need an efficient way to search the problem space tree. 

Now let s look at the problem space that we just navigated in Figure 3.6 to see all the branches and where else we could have gone under basic conditions. Two new enol structures from the protonation of the oxygen anion are very reasonable dead ends for this problem. A Af/ calculation will show that the enol is uphill from the reactant. The decisions and operations that we went through to navigate this example proton transfer mechanism problem space are flowcharted in Figure 3.7. 

Figure 3.6 Reasonable basic problem space for the example proton transfer mechanism. Acid routes have been dropped. Only proton transfer routes tire shown. Routes deprotonating carbons 3, 4, and 5 have been dropped because the proton transfer ATeq is less than 10 , and thus not useful.

The ATeq is greater than 1, indicating the proton transfer reaction favors products. Charge is balanced. Figure 3.8 shows each of the decisions in the problem space just navigated. 

Figure 3.8 Problem space for predicting a reasonable proton transfer in basic media.

We can modify our familiar addition and elimination surfaces to give us a combined simplified addition-elimination energy surface (Fig. 4.46). Although this system is further complicated by additional proton transfer reactions, we can get an overview of the problem space with this simplified surface as a map. The reactants are in the upper left comer. 

Draw the problem space for the following reactant prediction problem. Select the best of two possible substitution alternatives. Hint look at the proton transfer reaction. 

Keep your scratch sheets neat. Be organized on the scratch paper so you can trace your thoughts and be able to go back to other ideas and check your thinking without getting lost. Remember, you are exploring unknown territory draw yourself a map of the problem space as you go. 

We are at a well-known trail junction, the starting point of the addition surface from Section 4.4.2. Figure 10.2 is a simplified addition surface serving as a problem space map to guide our decisions and to remind us of alternative possibilities, because the first answer we think of may not be the best. 

Figure 102 Simplified addition surface serving as a problem space map for example 10. 1.

It helps to understand the overall transformation before diving into the individual steps. We can get a good overview of the problem space by generalizing what has to happen First an addition has occurred to connect the two reactants, then probably some proton transfers to set up the next step, an elimination of water. This allows us to draw a simplified problem space to guide our route decisions (Fig. 10.3). 

Figure 10.3 Simplified problem space for imine formation, example 10.5.2.

We can see from our simplified problem space that there are three possible addition routes that should be considered the hetero Ad 2 addition (path p.t. followed by AdN),... 

We need to connect the two partners before we can make the double bond, so the addition must have occurred before the elimination. Since bonds are made by combination of nucleophile and electrophile, we can see that the addition is not ready to proceed. While the aldehyde carbonyl is an electrophilic electron sink, carbon 2 of the other partner is a mere methylene and not a nucleophile. Therefore we need to generate a nucleophile on carbon 2 before the reaction can proceed. The problem space for the overall process might look like Figure 10.6. 

Figure 10.6 Simplified problem space for aldol condensation, example 10.5.3.

An elimination of water gets us to the product. We now are close enough to product to restrict paths to ehmination pathways. From our simplified problem space in Figure 10.6, we need to determine whether the medium can improve our leaving group and then move to the reactant comer of the elimination surface (Section 4.3.1). Resonance forms ... 

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