Nitrile oxides structural chemistry

It is the purpose of the series to review the field of organic nitro chemistry in its broadest sense by including structurally related classes of compounds such as nitroamines, nitrates, nitrones, and nitrile oxides. It is intended that the contributors, who are active investigators in various facets of the field, will provide a concise presentation of recent advances that have generated a renaissance in nitro chemistry research. 

The chemistry of nitrile oxides has been well reviewed (see, for example, Grundmann et a/.59-61), and only those features which are pertinent to the synthesis of isoxazoles are summarized here. The electronic structure may be represented as a hybrid of the canonical forms 19-23. The formula 20 is commonly used, but formula 19 embodies their 1,3-dipolar character, and formula 23 their nitrosocarbenoid nature. 

REACTIONS OF COORDINATED LIGANDS - dealing with the chemistry of molecules such as oxygen, nitric and nitrous oxide, carbon dioxide, oximes, and nitriles STEREOCHEMISTRY, STRUCTURE, AND CRYSTAL ENGINEERING structure and stereochemistry involving lone pair effects, outer sphere interactions, and hydrogen bonding. 

Nitriles, RC=N, are considered derivatives of carboxylic acids because the nitrile carbon is in the same oxidation state as the carboxy carbon and because nitriles are readily converted into other carboxylic acid derivatives. This section describes the rules for naming nitriles, the structure and bonding in the nitrile group, and some of its spectral characteristics. Then it compares the chemistry of the nitrile group with that of other carboxylic acid derivatives. 

The THT and SMe2 adducts have structures of the type (18-B-V). Their chemistry has been extensively studied and it is summarized in Fig. 18-B-7. The diverse, and in some cases unique, reactivity of these compounds includes substitution with preservation of the geometry or with conversion to (MX4)2(/t-X)2 species, oxidative-addition,53 cluster formation, splitting of C—N bonds,54 and above all coupling of the molecules with triply bonded carbon atom.55 They catalytically trimerize and polymerize terminal acetylenes, and dimerize nitriles and isonitriles with incorporation of the new ligand into the complex. Another remarkable reaction of M2C16L3 is the metathesis of M=M and N=N bonds into two M=N bonds upon reaction with azobenzene. 

Nitriles are compounds that contain a cyano group, C=N, bonded to an alkyl group. Nitriles have no carbonyl group, so they are structurally distinct from carboxylic acids and their derivatives. The carbon atom of the cyano group, however, has the same oxidation state as the carbonyl carbon of carboxylic acid derivatives, so there are certain parallels in their chemistry. 

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