Transforms Functional group

Tran orm-based or long-range strategies The retrosynthetic analysis is directed toward the application of powerful synthesis transforms. Functional groups are introduced into the target compound in order to establish the retion of a certain goal transform (e.g., the transform for the Diels-Alder reaction, Robinson annulation, Birch reduction, halolactonization, etc.). 

Functional Group Transformations Functional group transformations help us in the conversion of a functional group to an aldehyde or a ketone without affecting the carbon skeleton of the molecule. Aldehydes can be synthesised by the oxidation of primary alcohols, or by the reduction of esters, acid chlorides, or nitriles. Since nitriles can be obtained from alkyl halides, this a way of adding an aldehyde unit (CHO) to an alkyl halide ... 

Capillary Electrophoresis Chemical Warfare Agents Chemical Weapons Convention Deuterated L-Alanine Triglycine Sulfate Dimethyl Ethylphosphonate Dimethyl Isopropylphosphonate Dimethyl Methylphosphonate Dimethyl Propylphosphonate Dimercaptotoluene Diffuse Reflectance Infrared Fourier Transform Functional Group Chromatograms Flame-Ionization Detector Fourier Transform Infrared Spectroscopy Gas Chromatography Gas Chromatography/Chemical Ionization/Mass Spectrometry Gas Chromatography/Chemical Ionization/Tandem Mass Spectrometry... 

We now find ourselves familiar with methods of constructing a carbon skeleton for an organic molecule, how to introduce and transform functional groups, and how to achieve the required selectivity. One could almost expect the rich arsenal of contemporary methods to enable the chemist to solve practically any problem of synthetic chemistry. Yet it is not quite so simple. It is imperative to be skillful in planning a synthesis, to be able not only to master its tactics, but its overall strategy as well. 

P(NB/MA) Functional Group Transformations. Functional group transformation is one approach which is possible for the alteration of the hydrolytic latency of P(NB/MA) copolymers. Of the potentially useful post-polymerization functionalizations of P( /MA), hydrolysis, alcoholysis (to yield half-esters), imidization, amidization, and reduction were explored briefiy(2d). 

Consideration of the reaction center or reaction site is of central importance in reaction searching. It does not suffice to specify the functional groups in the starting materials and in the products of a reaction when one is interested in a certain transformation. On top of that, one also has to specify that these functional groups shotfid participate directly in the reaction - that they should be part of the reaction center. 

A catalytic enantio- and diastereoselective dihydroxylation procedure without the assistance of a directing functional group (like the allylic alcohol group in the Sharpless epox-idation) has also been developed by K.B. Sharpless (E.N. Jacobsen, 1988 H.-L. Kwong, 1990 B.M. Kim, 1990 H. Waldmann, 1992). It uses osmium tetroxide as a catalytic oxidant (as little as 20 ppm to date) and two readily available cinchona alkaloid diastereomeis, namely the 4-chlorobenzoate esters or bulky aryl ethers of dihydroquinine and dihydroquinidine (cf. p. 290% as stereosteering reagents (structures of the Os complexes see R.M. Pearlstein, 1990). The transformation lacks the high asymmetric inductions of the Sharpless epoxidation, but it is broadly applicable and insensitive to air and water. Further improvements are to be expected. 

Our first three chapters established some fundamental principles concerning the structure of organic molecules and introduced the connection between structure and reactivity with a review of acid-base reactions In this chapter we explore structure and reactivity m more detail by developing two concepts functional groups and reaction mechanisms A functional group is the atom or group m a molecule most respon sible for the reaction the compound undergoes under a prescribed set of conditions How the structure of the reactant is transformed to that of the product is what we mean by the reaction mechanism... 

It IS convenient m equations such as this to represent generic alcohols and alkyl halides as ROH and RX respectively where R stands for an alkyl group In addition to con venience this notation lets us focus more clearly on the functional group transformation that occurs the OH functional group of an alcohol is replaced as a substituent on car bon by a halogen usually chlorine (X = Cl) or bromine (X = Br)... 

Thionyl chloride and phosphorus tribromide are specialized reagents used to bring about particular functional group transformations For this reason we won t present the mechanisms by which they convert alcohols to alkyl halides but instead will limit our selves to those mechanisms that have broad applicability and enhance our knowledge of fundamental principles In those instances you will find that a mechanistic understand mg IS of great help m organizing the reaction types of organic chemistry... 

Chemical reactivity and functional group transformations involving the preparation of alkyl halides from alcohols and from alkanes are the mam themes of this chapter Although the conversions of an alcohol or an alkane to an alkyl halide are both classi tied as substitutions they proceed by very different mechanisms... 

This concludes discussion of our second functional group transformation mvolv mg alcohols the first was the conversion of alcohols to alkyl halides (Chapter 4) and the second the conversion of alcohols to alkenes In the remaining sections of the chap ter the conversion of alkyl halides to alkenes by dehydrohalogenation is described... 

Predict the major organic product of each of the following reactions In spite of the struc tural complexity of some of the starting matenals the functional group transformations are all of the type described in this chapter... 

Functional group transformations of epoxides rank among the fundamental reactions of organic chemistry and epoxides are commonplace natural products The female gypsy moth for example attracts the male by emittmg an epoxide known as disparlure On detechng the presence of this pheromone the male follows the scent to its ongm and mates with the female... 

Often more than one synthetic route may be available to prepare a particular com pound Indeed it is normal to find m the chemical literature that the same compound has been synthesized m a number of different ways As we proceed through the text and develop a larger inventory of functional group transformations our ability to evaluate alternative synthetic plans will increase In most cases the best synthetic plan is the one with the fewest steps... 

The most frequently encountered nucleophiles in functional group transformations are anions which are used as their lithium sodium or potassium salts If we use M to represent lithium sodium or potassium some representative nucleophilic reagents are... 

Representative Functional Group Transformations by Nucleophilic Substitution Reactions of Alkyl Halides... 

Section 8 1 Nucleophilic substitution is an important reaction type m synthetic organic chemistry because it is one of the mam methods for functional group transformations Examples of synthetically useful nucleophilic sub stitutions were given m Table 8 1 It is a good idea to return to that table and review its entries now that the details of nucleophilic substitution have been covered... 

A second strategy for alkyne synthesis involving functional group transformation reactions is described m the following section... 

Chlorination is carried out m a manner similar to brommation and provides a ready route to chlorobenzene and related aryl chlorides Fluormation and lodmation of benzene and other arenes are rarely performed Fluorine is so reactive that its reaction with ben zene is difficult to control lodmation is very slow and has an unfavorable equilibrium constant Syntheses of aryl fluorides and aryl iodides are normally carried out by way of functional group transformations of arylammes these reactions will be described m Chapter 22... 

Both the Clemmensen and the Wolff-Kishner reductions are designed to carry out a specific functional group transformation the reduction of an aldehyde or ketone carbonyl to a methylene group Neither one will reduce the carbonyl group of a carboxylic acid nor... 

In contrast to alcohols with their nch chemical reactivity ethers (compounds contain mg a C—O—C unit) undergo relatively few chemical reactions As you saw when we discussed Grignard reagents m Chapter 14 and lithium aluminum hydride reduc tions m Chapter 15 this lack of reactivity of ethers makes them valuable as solvents m a number of synthetically important transformations In the present chapter you will learn of the conditions m which an ether linkage acts as a functional group as well as the methods by which ethers are prepared... 

The chemistry of carboxylic acids is the central theme of this chapter The impor tance of carboxylic acids is magnified when we realize that they are the parent com pounds of a large group of derivatives that includes acyl chlorides acid anhydrides esters and amides Those classes of compounds will be discussed m Chapter 20 Together this chapter and the next tell the story of some of the most fundamental struc tural types and functional group transformations m organic and biological chemistry... 

The carbon-carbon bond forming potential inherent m the Claisen and Dieckmann reac tions has been extensively exploited m organic synthesis Subsequent transformations of the p keto ester products permit the synthesis of other functional groups One of these transformations converts p keto esters to ketones it is based on the fact that p keto acids (not esters ) undergo decarboxylation readily (Section 19 17) Indeed p keto acids and their corresponding carboxylate anions as well lose carbon dioxide so easily that they tend to decarboxylate under the conditions of their formation... 

The two most useful supplementary techniques for the light microscope are EDS and FTIR microscopy. Energy dispersed x-ray systems (EDS) and Eourier-transform infrared absorption (ETIR) are used by chemical microscopists for elemental analyses (EDS) of inorganic compounds and for organic function group analyses (ETIR) of organic compounds. Insofar as they are able to characterize a tiny sample microscopically by PLM, EDS and ETIR ensure rapid and dependable identification when appHed by a trained chemical microscopist. 

A predictive macromolecular network decomposition model for coal conversion based on results of analytical measurements has been developed called the functional group, depolymerization, vaporization, cross-linking (EG-DVC) model (77). Data are obtained on weight loss on heating (thermogravimetry) and analysis of the evolved species by Eourier transform infrared spectrometry. Separate experimental data on solvent sweUing, solvent extraction, and Gieseler plastometry are also used in the model. 

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