Logic-centered approach

The Japanese program system AlPHOS is developed by Funatsu s group at Toyo-hashi Institute of Technology [40]. AlPHOS is an interactive system which performs the retrosynthetic analysis in a stepwise manner, determining at each step the synthesis precursors from the molecules of the preceding step. AlPHOS tries to combine the merits of a knowledge-based approach with those of a logic-centered approach. 

In the direct-associative approach the chemist has available a number of subunits which he can bring together using standard laboratory reactions with which he is already familiar. This empirical approach is obviously limited to known reactions and subunits. The logic-centered approach on the other hand consists of the generation of sets of intermediates which form a synthetic tree which is used to lead to the target molecule. The different branches of this tree are the alternative routes one would choose or reject. In practice, most chemists use an approach which is a mixture of both. 

The logic centered approach leads to a restricted set of structures that may be converted in a single step to the target. Each new structure can. in turn, be converted to a new structure. The purpose of the retrosynthetic analysis is to generate synthetic intermediates (the synthesis tree) that terminate with a number of starting materials.Corey et al. outlined this approach in 1964 in his synthesis of longifolene (73), which is shown in Scheme 10.4.- 2 This synthesis used the 33 ieland-Miescher ketone (72) as the starting material. - Analyses... 

That there is a need for such an application is made apparent by the fact that a complete, logic-centered synthetic analysis of a complex organic structure often requires so much time, even of the most skilled chemist, as to endanger or remove the feasibility of the approach. It would be a great advantage if at least a part of the necessary analysis could be performed rapidly and accurately by computer. ... 

Figure 10 was prepared by a Dow technology center as a logic diagram to illustrate an approach to be taken to determine how often a critical instrument loop should be tested. 

These are the most extensively studied class of poly(pyrazolyl)borate compounds for platinum and palladium, and rank among the most numerous and varied. The literature includes examples of M(II) and M(IV) centers in cationic, neutral, and anionic complexes, with all possible coordination numbers four to six represented moreover, many of these complexes are readily interconverted. This section will therefore be organized according to oxidation state, as the most logical approach. 

Parker and Williams recently reported NAND logic action in the terbium complex 16.[S8] The delayed emission of the lanthanide ion is switched off when H+ and 02 are present simultaneously. Protonation of the phenanthridine side chain causes its triplet excited state to approach theTb(m) 5D4 excited state energetically. This leads to equilibration of these two excited states and sharing of their properties. Thus, the metal-centered state displays the 02 sensitivity usually only found in organic triplets. 

Exercise 7.6. The solid-state compound Mg2CoH5 has been prepared and exhibits the same metal lattice as MgFeH6. Using the Zintl-Klemm approach and your knowledge of molecular coordination chemistry, suggest a logical geometry for the H atoms around the Co center. 

Approach writing the mechanism in a logical fashion. For example, if the reagent is a strong base, look for acidic protons in the substrate, then look for a reasonable reaction for the anion produced. If the anion formed by deprotonation has a suitable leaving group, its loss would lead to overall elimination. If the anion formed is a good nucleophile, look for a suitable electrophilic center at which the nucleophile can react. (For further detail, see Chapter 3.)... 

We start displaying the electrophoretic mobility for latexes JLl (Figure 3.3a) and SNIO (Figure 3.3b) as a function of the Mg(N03)2 (Mg++ is the counterion). In both cases, experimental data are represented by symbols with their experimental error bars (estimated from the standard deviation of a set of measurements), whereas theoretical predictions are plotted by fines (solid and dashed fines for the HNC/MS A and PB approaches). To begin with the discussion, we center on the experimental results. In order to simplify the discussion, we will refer to the electrophoretic mobility in absolute value hereafter. Accordingly, the electrophoretic mobilities of the more charged latex (SNIO) are logically... 

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