Structure and Bonding in Amines

Greenwell, H. C., Harvey, M. J., Boulet, R, Bowden, A. A., Coveney, P. V, and Whiting, A. 2005. Interlayer structure and bonding in nonswelling primary amine intercalated clays. Macromolecules 38 6189-6200. 

In most amines, the nitrogen atom is sp3 hybridized, with a pyramidal structure and bond angles close to 109°. In urea, both nitrogen atoms are found to be planar, with bond angles close to 120°. Explain this surprising finding. (Hint Consider resonance forms and the overlap needed in them.)... 

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. 

Nitrogen s unshared electron pair is of major importance in understanding the structure and properties of amines. Alkylamines have a pyramidal arrangement of bonds to nitrogen, and the unshared electron pair... 

Two complexes containing a dilithiated stilbene fragment have been prepared and isolated from the reactions of 1,2-diphenylethane with N-chelated butyl-lithium reagents. " The molecular and crystal structures of these compounds, stilbene bis(lithium tetramethylethylenediamine) (Figure 4a) and stilbene bis(lithium pentamethyldiethylenetriamine) (Figure 4b), have been determined by X-ray diffraction techniques. Each structure contains two amine-solvated Li atoms located above and below the olefinic bond of a stilbene molecule. The stilbene molecule is planar in both structures, and is in a trans configuration about the C(7)—C(7 ) bond, which is ca. 0.01 nm longer than that in trans-stilbene. " The optical and "C n.m.r. spectra of THF solutions of the related dilithium and disodium salts of tetraphenylethylene dianion, as well as the spectra of their mixtures, have been examined. " The data can be rationalized in terms of the... 

Several tandem reaction sequences have been developed for indole synthesis featuring a Buchwald-Hartwig aryl amination as one component. For instance, a tandem double JV-arylation of substrate 5 leads to indoles 6 through a cascade of C-N bond forming reactions. A range of structurally and electronically diverse amines can be used successfully in this transformation. 

The hydrolysis of simple imines occurs readily in aqueous acid and has been studied in great detail by kinetic methods. The precise mechanism is a fimction of the reactant structure and the pH of the solution. The overall mechanism consists of an addition of water to the C=N bond, followed by expulsion of the amine from a tetrahedral intermediate. ... 

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