Worked Product Prediction Examples

using the electron sink as a guide, find the few electron flow pathways that fit those sources and sinks (Chapter 7). Look at restrictions to limit the choice of pathways, such as acidic vs. basic media. Narrow down the choice of pathways further by using steric, electronic, and solvent limitations if available. Combine the best source with the best sink through an appropriate pathway to yield a preliminary product (Chapter 8). Only about half of all the possible sources and sinks are common, and those common combinations were outlined in the correlation matrix of Table 8.1 and discussed in the sections that followed. Be aware of alternatives like competing paths (Chapter 4) and decisions like substitution vs. elimination (Chapter 9). 

Finally, have faith in the predictive process and allow it to carry you to the answer. Do not try to shorten the process to get to the answer by combining or skipping steps. Don t panic and force an answer because you can t see the answer from the beginning. 

In these examples, if several routes go to the same compound, for simplicity only the more reasonable will be shown. Try to work each step before looking at the answer. 

1 Predict the Product of Reaction of Ethyi Acetoacetate, Ethoxide, and 1-Bromobutane 

The first step is in basic medium ethoxide has a pATabH of 16. Sources The ethoxide anion. Leaving groups Only ethoxide on the ester. Sinks The ketone is a polarized multiple bond, and the ester is a polarized multiple bond with a leaving group. Acidic Hs The CH2 between the two carbonyls the most acidic, p/fa 10.7 the methyl on the carbonyl is the next most acidic, pA a 19. Resonance forms help us understand the polarization of our reactants. 

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What if the rate-determining step is the second step This becomes a bit more difficult to determine because an intermediate is involved in the rate law. Because intermediates are usually quite unstable, it is difficult to predict their concentrations. If the second step is slow, then you have to assume that the first step quickly produces an intermediate. However, if the second step is slow, the intermediate may not be able to break apart to form products. What generally happens in this case is that the intermediate will fall apart into the reactants again. The reactants will reform the intermediate, and equilibrium will begin between the intermediate and the reactants. For mechanisms where a slow step is preceded by a fast one, it is assumed that equilibrium is established in the fast reaction. Let s see how this works in an example. In the reaction... 

Software to predict the properties of formulated products is made more powerful by a recursive procedure which can use formulas stored in files as raw materials. Particular care must be taken with program flow control and data structures for the recursion to be effective. This paper illustrates these issues using an example derived from a working formulation system for coatings development. 

The solvent dependence of the reaction rate is also consistent with this mechanistic scheme. Comparison of the rate constants for isomerizations of PCMT in chloroform and in nitrobenzene shows a small (ca. 40%) rate enhancement in the latter solvent. Simple electrostatic theory predicts that nucleophilic substitutions in which neutral reactants are converted to ionic products should be accelerated in polar solvents (23), so that a rate increase in nitrobenzene is to be expected. In fact, this effect is often very small (24). For example, Parker and co-workers (25) report that the S 2 reaction of methyl bromide and dimethyl sulfide is accelerated by only 50% on changing the solvent from 88% (w/w) methanol-water to N,N-dimethylacetamide (DMAc) at low ionic strength this is a far greater change in solvent properties than that investigated in the present work. Thus a small, positive dependence of reaction rate on solvent polarity is implicit in the sulfonium ion mechanism. 

When painting a wall, better coverage is assured when the roller passes over the same area several times from different directions. It is the opinion of the author that this technique works well in teaching chemistry. Therefore, a second objective has been to stress fundamental principles in the discussion of several topics. For example, the hard-soft interaction principle is employed in discussion of acid-base chemistry, stability of complexes, solubility, and predicting reaction products. Third, the presentation of topics is made with an effort to be clear and concise so that the book is portable and user friendly. 

When working with non-radiolabeled drugs the major challenge is to find metabolites in the biological matrices. Because the enzymes responsible for metabolism are quite well characterized metabolic changes can partially be predicted. For example hydroxylation of the parent drug is in many cases the principal metabolic pathway. From a mass spectrometric point of view it results in an increase of 16 units in the mass spectrum. In the full-scan mode an extracted ion current profile can be used to screen for potential metabolites. In a second step a product ion spectrum is recorded for structural interpretation. Ideally, one would like to obtain relative molecular mass information and the corresponding product ion spectrum in the same LC-MS run. This information can be obtained by data dependant acquisition (DDA), as illustrated in Fig. 1.39. 

The mechanistic and synthetic groundwork has been unequivocally established for the consecutive cycloreversion transannular ene reaction sequence, from which /ra/w-decalin derivatives with a hydroxyl group at the ring junction are produced.146,147 As an example, the thermally induced cycloreversion of the ester 43 at 200°C affords 45 in an astonishing 96% yield.146 Presumably the initial cycloreversion product 44 is converted by a transannular ene reaction to generate the decalin 45.146 However, not all the cycloreversion reactions proceed to give a single product as predicted, as can be shown by the examples collected in Table 7. In fact, closer inspection of work already reported has shown that complex product mixtures are usually obtained from cyclobutane cycloreversion reactions.143,148 152... 

Other workers (115-124 for example) have also centered their efforts on the role of phytic acid on zinc and iron bioavailabiliy from both soy and wheat products. It has been suggested (120) that the phytate-to-zinc molar ratio could be used to predict zinc bioavailability in high-phytate foods. Several groups (115, 117), including ours (113), 1 least partially supporT this hypothesis. However, recent work from our laboratory (112) involving soy protein of similar phytate-to-zinc molar ratios clearly demonstrates that zinc bioavailability is also altered by food processing. In this study, zinc from neutralized soy concentrates and isolates was shown to be less available to the rat than was the corresponding acid-precipitated products. This is unfortunate as alkaline conditions are commonly utilized for soy and other plant proteins to obtain beneficial functional properties. 

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