Nitrogen atoms

Zhdankin s azide sonrce 11 can affect azidation a to a nitrogen atom through the same mechanism discussed in the previous section (see Section 2.2.6. ).  

and coworkers used t-butyl hydroperoxide to form a carbon-centered radical a to the nitrogen of an amide 30. The carbon-centered radical can abstract a sulfur atom from a disulfide 31 to form a new C—S bond. This is one of the few transition metal-free C—S bond-forming reactions.  

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The nonbonding electrons of the nitrogen atom are important in determining spin re-pairing, and thus the conical intersections. This is the physical origin of the topicity concept developed by Salem and co-workers [2,30]. Two different spin... 

In this molecule, the aluminium receives a pair of electrons from the nitrogen atom. The nitrogen atom is referred to as a donor atom and the aluminium as an acceptor atom. Once the bond is formed it is identical to the covalent bond of previous examples it differs... 

The strongly electronegative (p. 49) chlorine atom becomes a chloride ion, the proton accepting the electron pair donated by the nitrogen atom. A similar reaction occurs when ammonia is passed into water, but to a much lesser extent as oxygen in water is a poorer donor of the electron pair ... 

The element before carbon in Period 2, boron, has one electron less than carbon, and forms many covalent compounds of type BX3 where X is a monovalent atom or group. In these, the boron uses three sp hybrid orbitals to form three trigonal planar bonds, like carbon in ethene, but the unhybridised 2p orbital is vacant, i.e. it contains no electrons. In the nitrogen atom (one more electron than carbon) one orbital must contain two electrons—the lone pair hence sp hybridisation will give four tetrahedral orbitals, one containing this lone pair. Oxygen similarly hybridised will have two orbitals occupied by lone pairs, and fluorine, three. Hence the hydrides of the elements from carbon to fluorine have the structures... 

What effect does the presence of a lone pair of electrons on the nitrogen atom have on ... 

Ammonia as a donor molecule. Because of the presence of the lone pair of electrons on the nitrogen atom, ammonia can behave as an electron pair donor. For example, ammonia abstracts a proton from a water molecule producing the tetrahedral ammonium, NH4, ion and forms the compounds HjN- AlClj and HjN- BClj. 

Pure hydrazine is a colourless liquid, melting point 275 K, and boiling point 387 K. It is surprisingly stable for an endothermic compound = -i- 50.6 kJ mol ). Each nitrogen atom has a lone pair of electrons and either one or both nitrogen atoms are able to accept protons to give and the less stable... 

Perhaps the most important complex of iron(II) is heme (or haeme). Haemoglobin, the iron-containing constituent of the blood, consists essentially of a protein, globin, attached through a nitrogen atom at one coordination position of an octahedral complex of iron(II). Of the other five coordination positions, four (in a plane) are occupied by nitrogen atoms, each of which is part of an organic... 

Cobalt compounds have been in use for centuries, notably as pigments ( cobalt blue ) in glass and porcelain (a double silicate of cobalt and potassium) the metal itself has been produced on an industrial scale only during the twentieth century. Cobalt is relatively uncommon but widely distributed it occurs biologically in vitamin B12 (a complex of cobalt(III) in which the cobalt is bonded octahedrally to nitrogen atoms and the carbon atom of a CN group). In its ores, it is usually in combination with sulphur or arsenic, and other metals, notably copper and silver, are often present. Extraction is carried out by a process essentially similar to that used for iron, but is complicate because of the need to remove arsenic and other metals. 

With RAMSES, the conjugation between the C=0 rr-system and the lone pair of the nitrogen atom in the amide group is taken into account (see Figure 2-51b). 

Figure 2-51. a) The rotational barrier in amides can only be explained by VB representation using two resonance structures, b) RAMSES accounts for the (albeit partial) conjugation between the carbonyl double bond and the lone pair on the nitrogen atom. 

Figure 2-52. a) Two semipolar resonance structures are needed in a correct VB representation of the nitro group, b) Representation of a nitro group by a structure having a pentavalent nitrogen atom, c) The RAMSES notation of a nitro group needs no charged resonance structures. One jr-system contains four electrons on three atoms. 

Figure 7-6. Graphical representation of the procedure for calculating the effective polarizability on the nitrogen atom of 2-aminopropane.

An effective polarizability, reflecting the stabilization of a positive charge on the protonated nitrogen atom through polarizability, is calculated by Eq, (16). 

Thus, the values calculated for effective polarizability at the nitrogen atom for a series of 49 amines carrying only alkyl groups was correlated directly with their proton affinities, a reaction that introduces a positive charge on the nitrogen atom by protonation (Figure 7-7) [40. ... 

Figure 10.3-40. The rating for the disconnection strategy carbon-heteroatom bonds is illustrated, Please focus on the nitrogen atom of the tertiary amino group. It is surrounded by three strategic bonds with different values. The low value of 9 for one ofthese bonds arises because this bond leads to a chiral center. Since its formation requires a stereospecific reaction the strategic weight of this bond has been devalued. In contrast to that, the value of the bond connecting the exocyclic rest has been increased to 85, which may be compared with its basic value as an amine bond.

Dissolve ca. 0 2 g. of product (I) in cold ethanol, and add with shaking 1-2 drops of dilute sulphuric acid. A deep purple coloration appears at once. This shows that salt formation has occurred on the quinoline nitrogen atom to form the cation (Ha), which will form a resonance hybrid with the quinonoid form tils). [Note that the forms (IIa) and (11b) differ only in electron position, and they are not therefore tautomeric.] If, hoAvever, salt formation had occurred on the dimethylaniino group to give the cation (III), thrs charge separiition could not occur, and the deep colour would be absent. 

Now add more dilute sulphuric acid drop by drop the colour almost completely fades, as salt formation occurs on both nitrogen atoms with suppression of the resonance hybrid formation. 

A purple or rose pink coloration i produced when sodium hydroxide and dilute copper sulphate solution are added to compounds containing two -CONH- groups attached either to one another, or to the same nitrogen atom, or to the same carbon atom. It is therefore also given by oxamide, NHjCO CONH, malonamide, NHtCO-CH, CONH, and by proteins and peptides. In fact the -COKH - is often spoken of as the peptide linkage. 

How would w e obtain the MNDO approximations to the properties of the nitrogen atom) ... 

Compounds with one cychcally bound nitrogen atom. 

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