Bonding in amines

Properties and Reactions. Amine boranes are usually colodess, crystalline compounds, which exhibit sharp melting points and thermal stability when pure. Primary and secondary amine boranes are generally soHds at ambient temperatures. With the exception of trimetbylamine borane, the ahphatic /-amine boranes are Hquids. The nature of the bonding in amine boranes has been the subject of theoretical investigations (21—23). 

The nature of the bonding in amine-boranes and related adducts has been the subject of considerable theoretical discussion and has also been the source of some confusion. Conventional representations of the donor-... 

The acidification of N—H bonds in amines and stabilization of the amide anion resulting on dissociation can be achieved by a variety of groups, which all have electron-withdrawal properties in common. These anions can then act as N-donors towards Cd or Hg. 

Considerable controversy surrounds the nature of the bonding in amine oxides and analogous phosphine and arsine oxides. These species are often depicted in textbooks as double-bonded (0=PH3, 0=AsH3) in order to rationalize the unusually short bond lengths. However, both theoretical wavefunction analysis53 and NMR... 

Using simple orbital interaction considerations, explain the polarity of the N— bond in amine oxides. 

Typical examples for type 2 are the cleavage of the carbon-oxygen bond in benzylic ethers (X = OR) either directly or indirectly via triarylamine cation radicals [49] (Eq. 22.42), the cleavage of the carbon-nitrogen bond in amines (X = NR2) [50] (Eq. 22.43), and the cleavage of the carbon-sulfur bond in sulfides (X = SR) [51] (Eq. 22.44) ... 

In contrast, few examples of reductive elimination reactions that form the C-N bond in amines are known. Only in the past several years have complexes been isolated that undergo these reactions [49-54]. These reductive eliminations are the crucial C-N bond-forming step of the aryl halide and triflate amination chemistry discussed in this review. Information on how these reactions occur, and what types of complexes favor this process, has been crucial to the understanding and development of new amination catalysts [50],... 

For hydrates, the question is, to what extent does the nitrogen atom lone pair contribute to hydrogen bonding in amine hydrates Hydrogen bonding is expected to explain the difference between gaseous and solid ammonia couplings. 

The bonding in amines is similar to that in ammonia. The nitrogen atom is sp -hybridized, the three substituents are directed to three corners of a tetrahedron, and the lone pair of nonbonding electrons occupies the fourth corner of the tetrahedron. An interesting feature of this tetrahedral structure is that amines undergo a rapid pyramidal inversion, which interconverts mirror-image structures. 

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