Nitrogen in amines

The geometry at nitrogen in amines is discussed in an arti cle entitled What Is the Geometry at Trigonal Nitro gen T in the January 1998 issue of the Journal of Chem ical Education pp 108-109... 

Since it has been observed that the hydrogen atoms attached to nitrogen in amines were not easily abstractable in free radical reactions (6, 74), it may be assumed that the aldehydic part of the formamide molecule will be more reactive in the photoaddition reactions than the amino function, thus leading to the following addition reaction with terminal olefins,... 

Oxidative Coupling of C-H Bonds Adjacent to the Nitrogen in Amines. 283... 

In sum, the course of heteroatom oxidation appears to be sensitive to the oxidation potential of the heteroatom, the acidity of hydrogens on the adjacent carbon, and steric factors. The bulk of the evidence suggests that oxidation of the nitrogen in amines generally involves electron abstraction followed primarily by A-dealkylation if a labile proton is present, or nitrogen oxidation if it is not. As the nitrogen oxidation potential increases, there is a shift toward direct insertion into the C-H bond, as is thought to occur in the A-dealkylation of amides. 

A dipole moment of 1.46 x 10 Cm (4.38 D) for the nitrogen-oxygen bond is larger than the moments of other semipolar bonds (3). The spatial arrangement around nitrogen in amine oxides is tetrahedral as in quaternary ammonium salts. Tetrahedral configuration was demonstrated by Meisenheimer, who separated iV-ethji-iV-methjianiline iV-oxide [825-19-4] into its optical isomers (4), and later confirmed by electron diffraction studies ( ) ... 

The donor substituent perturbation of lone pair centers is transparently demonstrated in sulfides (Fig. 7). The parent molecule H2S exhibits for its Jt-type sulfur lone pair perpendicular to the molecular plane an ionization needle at 10.5 eV [20]. Two (H3C)3SiCH2 substituents broaden the needle considerably, indicating charge delocalization and lower its first vertical ionization potential by 2.5 eV = 241 kJ mol to 8.0 eV. In the dimethyl sulfide derivative with three RsSi substituents at the same carbon center, the total shift reaches almost 3 eV (Fig. 7), an amazing demonstration of the extreme donor power of P-trimethylsilyl substituents. Tremendous substituent perturbations are also observed at other lone-pair heterocenters such as nitrogen in amines [1, 2b], with the ionization energies IE] lowered from 10.85 eV in NH3 to 7.66 eV in N(CH2SiR3)3, a difference of 3.19 eV ... 

The nitrogen in amines is sp hybridized, the nonbonding electron pair functioning as the equivalent of a substituent. This tetrahedral arrangement inverts rapidfy through a planar transition state. 

Dimethyl carbonate can be used for methylation of nitrogen in amine compounds at a temperature of 180°C under continuous-flow gas-liquid phase-transfer catalysis conditions (which involve transfer of organic ionic reactant species between water and an organic phase) as shown below for the methylation of aniline ... 

Scheme 1.2 Proposed alkynylation of an a-C-H bond of nitrogen in amines (top) and aldehdye-alkyne-amine (A ) coupling (bottom).

The proposed iminium intermediate in the CDC-type allgmylation implies that other C-H based pronueleophiles, besides terminal allqmes, can also couple with an a-sp C-H bond of a nitrogen in amines via the same process. Thus, we examined eleetron-rieh arenes as one such nucleophile via a cross-dehydrogenative Friedel-Crafts type arylation. Indole derivatives were coupled with N-aryl-THIQs under the CuBr/TBHP system to produce the desired CDC reaction product in good-to-excellent yields (Scheme 1.9). It is worth noting that the reaction was not sensitive to moisture or air, and that the desired product was obtained in reasonable yield even when the reaction was... 

The success of the sp C-H/sp C-H and sp C-H/sp C-H couplings led us to explore the possibility of the even more challenging CDC reaction between sp C-H and sp C-H bonds. We started with the reaction of an a-sp C-H bond of nitrogen in amines with nitroalkanes, which would provide aza-Henry-type reaction products. Using CuBr as the catalyst and TBHP as the terminal oxidant, various p-nitroamine derivatives were generated by this new methodology (Scheme 1.22). ... 

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