Reactions and Transformations

The use of Simplified Molecular Input Line Entry System (SMILES) as a string representation of chemical structure makes possible much of what has been discussed in earlier chapters of this book. A chemical reaction could be represented as a collection of SMILES, some identified as reactants and some as products. It is possible to define a table to do this, or perhaps use some arrays of character data types, but a syntax extension of standard SMILES allows reaction to be expressed easily. SMIRKS is an extension of SMILES and SMiles ARbitrary Target Specification (SMARTS). It is used to represent chemical transformations. SMIRKS can also be used in a transformation function to combine SMILES reactants to produce SMILES products. 

This chapter describes some of the aspects of SMIRKS and shows how it can be integrated into a relational database using new structural query language (SQL) functions. It discusses ways in which chemical transformations and reactions can be used to improve the robustness and usefulness of a chemical relational database. 

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One of the newer and more fmitful developments in this area is asymmetric hydroboration giving chiral organoboranes, which can be transformed into chiral carbon compounds of high optical purity. Other new directions focus on catalytic hydroboration, asymmetric aHylboration, cross-coupling reactions, and appHcations in biomedical research. This article gives an account of the most important aspects of the hydroboration reaction and transformations of its products. For more detail, monographs and reviews are available (1—13). 

Experiments on photochemical reactions and transformations have been carried out under a number of different conditions ... 

Miscellaneous reactions and transformations involving homocyclic ring substituents 366... 

Geochemical mass balance studies (also known as input-output budgets) invoke a simple conservation-of-mass principle. If the flux of any element leaving a watershed (e.g., via streams), and the flux of that element into the watershed (e.g., via atmospheric precipitation) are known, the difference between the two can be calculated, and this difference must be due to the sum of all reactions and transformations involving that element which took place within the watershed. Pioneering mass balance studies on weathering profiles and/or small watersheds include those of Garrels and Mackenzie (,51, 52) and Cleaves and Bricker and their... 

Reactions and transformation of DPhA during storage and aging of smokeless proplnts using it as a stabilizer have been studied by many investigators and results are reported in Refs 2, 4, 5, 6, 7, 8, 15, 17, 20, 21 and 22... 

Several sensors have been developed to measure substrates in biological fluids. The structure of the membrane in these biosensors is quite complex. It generally contains a substrate-sensitive layer that includes a specific enzyme to catalyse a reaction and transform the analyte (or substrate). 

Chemical Energetics and Atomistics of Reactions and Transformations in Solids... 

A large amount of organic chemistry is concerned with the reactions and transformations of one functional group to another. An understanding of the functional group explains the particular set of properties associated with compounds within a series or family. ... 

The true stability ranges of the various oxides will be very difficult to establish because of the slow reaction and transformation rates, especially those occurring below about 600° C. There is a pronounced tendency for some of the phases to form and remain for long periods in a metastable state. Moreover, in samples of MoOs reduced in various ways crystals have occasionally been found which may... 

Some typical examples of the first two cases are listed in Tables 3 and 4, respectively. Since solid-state reactions and transformations are accelerated at elevated temperatures, high pressure synthesis almost automatically assumes treatments at elevated temperatures. Reaction times are usually short, 0.5-Ih. However, discrimination between these kinetic effects and thermodynamical stabihty should always be kept in mind. 

Diels Alder reactions. Two laboratories have reported use of 1 in Diels-Alder reactions and transformation of the resulting adducts into /3-amino alcohols. The reagent is only a moderately active dienophile, somewhat more reactive than vinylene carbonate. The parent heterocycle, 4-oxazoIine-2-one, is less useful because of thermal instability at the temperatures usually required for cycloaddition. The adducts from 1 can be deacetylated by treatment with KOH or ammonium hydroxide in CH3OH at 20°. On hydrolysis with KOH or NaOH in refluxing methanol or ethanol the adducts give, cw-/8-amino alcohols in good yield. 

V-Sulfinyl carbamates derived from chiral alcohols show high enantioselectivity in Lewis acid catalyzed [2 + 2] and [4 + 2] cycloadditions with alkenes and 1,3-dienes, respectively. In the presence of 1.2 equivalents of tin(IV) chloride, the chiral /V-sulfinyl carbamate 5 derived from fraw-2-phenylcyclohexanol reacts with a variety of alkenes to give diastereomeric sulfmamide derivatives 691,98. Very high asymmetric induction at both sulfur and carbon is observed. A detailed discussion of this ene reaction and transformations of the ene adducts thus formed is given in Section D.4.6. 

Oxacyclopentene 17 underwent a variety of transformations, such as Tamao oxidation, yielding the /3-hydroxy ketone 18 efficiently, an epoxidation reaction, and transformation into 1,4-diene 20 (Scheme 2) <2005OL4995>. 

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