Direct substitution strategies

A direct substitution strategy can be used for equations of the form... 

Methanol substitution strategies do not appear to cause an increase in exposure to ambient formaldehyde even though the direct emissions of formaldehyde have been somewhat higher than those of comparable gasoline cars. Most ambient formaldehyde is in fact secondary formaldehyde formed by photochemical reactions of hydrocarbons emitted from gasoline vehicles and other sources. The effects of slightly higher direct formaldehyde emissions from methanol cars are offset by reduced hydrocarbon emissions (68). 

Serghides compared nine explicit approximation formulas. Various formulas gave good results but none exactly compatible with the Colebrook equation. Here is a new strategy to solve this equation. The method uses direct substitution repeatedly the results are quite accurate. 

NEM of equation (2) for perturbations in the coupling coefficients of the nonlinear NEM strategy [7]. For the treatment of local thermal and hydraulic and fission product feedbacks, an additional second order accurate, nonlinear correction is applied in the evaluation of equation (3). This correction is obtained by direct substitution of the uncorrected power density response of equation (3) into analytical sensitivities for the change in cross-section with locd power [14]. 

While prevention of substitution or cyclisation reaction at an electrophilically more reactive site is one of the techniques to promote reaction at the less reactive site, strategies to specifically direct substitution at the less reactive position are also known. Phenol, for example, is specifically formylated at ortho position in alkaline medium Cinnamic acid is specifically nitrated at ortho position by N Oj. It is possible that in such reactions, the first step is the complexation of the reagent with the substituent already present, which then favours the attack of the reagent at the sterically close (to the complexing group) aromatic position which is ortho to the substituent already present. 

This could be done by directly substituting the xi + X2 = 1 relation into Eq. (7.3) to eliminate Xi or X2, but we will use a different strategy, with which we will obtain simpler models. Since X1+X2 is always equal to 1, we can introduce it as a coefficient of 60 in Eq. (7.3) without affecting the equation ... 

Direct substitution of a bulk petrochemicaL This strategy impUes that a bulk chemical, which is presently produced from petrochemical resources, would be substituted by an identical substance, produced from biomass with the help of biotechnology. The substitute could either be the building block itself or a derivative of the building block. Advantages of this strategy will be that the markets for these products already exist and the market drivers are well known, which substantially reduces the uncertainty. 

Proven product. The substitute could be a proven product This substrategy partly overlaps with the strategy direct substitution of a bulk petrochemical, but differs from it as it often also allows new or broader uses of the proven product As the product is already proven, the market risks are reduced. 

From a chemist s point of view, the common feature of the many spiro-linked compounds synthesized so far is the central core of spirobifluorene (1), which is substituted with equal or different substituents in the 2,2 and 7,7 positions, and, in some cases, also in the 3 and 6 or in the 4 and 4 positions, as shown in Fig. 3. There currently exist several pathways to the synthesis of spiro-Unked functional materials, whereas the choice of the right pathway depends on the desired substitution pattern. Compounds, which are fully symmetrically substituted in all fom para positions, i.e., R1 = R2 = R3 = R4, are generally synthesized from spirobifluorene itself. This strategy is also appUed for spiro compoimds with a synunetrically sixfold substitution pattern in the 2, 2, 4, 4, 7, and 7 positions. In the case of the horizontally unsymmetrical compounds, in which Rl = R2 R3 = R4, a more complex strategy has to be applied. Vertically unsynunetrical spiro compounds, in which R1 = R3 R2 = R4, can be accessed by direct substitution of spirobifluorene provided that the first two groups entering in the 2 and 2 positions deactivate the 7 and 7 positions, so that a subsequent substitution in these positions can be controlled. 

In the last example, a more direct approach to make the vinyl group may be via a Wittig strategy from a nicotinic aldehyde or via a direct aromatic substitution strategy. It should be noted that the Wittig and Heck reactions were known at the time the Merck, Gates, and Martin plans of quinine were disclosed. 

Applying Directing-Group Strategies in Electrophilic Aromatic Substitutions... 

Strategy Problem 1 The wrong substitution pattern . Making aromatic compounds m-substituted with two o -directing groups is always a problem. What strategies can you suggest An example (TM 412) is the alkyl hahde used in the synthesis of some steroids. 

---