The CH3—N Group

Amine derivatives with positively charged nitrogen atoms commonly occur in salts, in co-ordination compounds involving ammonia and in zwitterion structures. The latter have been discussed in the previous chapter, and will not be reconsidered here. 

Hydrochlorides of simple primary amines have been little studied, but appear similar to those of amino-acids. Methylamine hydrochloride, for example, absorbs at 3075 cm and at 2972 cm , and has an NH deformation band [84] at 1617 cm . In hydroxylamine hydrochloride the NH bonds are more strongly associated and are assigned [84] at 2955 cm and 2667 cm .  

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Tertiary amines are extremely difficult to identify spectroscopically. The C—N stretching band in aromatics can be identified in some cases, but there is no satisfactory correlation for aliphatic materials. The possibility of identification of the CH3 —N group is also discussed. 

Another arylation reaction which uses arenediazonium salts as reagents and is catalyzed by copper should be discussed in this section on Meerwein reactions. It is the Beech reaction (Scheme 10-49) in which ketoximes such as formaldoxime (10.13, R=H), acetaldoxime (10.13, R=CH3), and other ketoximes with aliphatic residues R are arylated (Beech, 1954). The primary products are arylated oximes (10.14) yielding a-arylated aldehydes (10.15, R=H) or ketones (10.15, R=alkyl). Obviously the C=N group of these oximes reacts like a C = C group in classical Meerwein reactions. It is interesting that the addition of some sodium sulfite is necessary for the Beech reaction (0.1 to 0.2 equivalent of CuS04 and 0.03 equivalent of Na2S03). 

Explain why the axial strain eneigies for the —C=N group and the —C=CH group are much smaller than that for the CH3 group. 

However, it is still common to find references to an older system of nomenclature. In this system, the total number of carbon atoms in the chain is indicated by the stem of the name chosen while the particular configuration that the carbon atoms adopted is indicated by the use of a distinguishing prefix. A straight chained molecule is given the prefix normal, which is abbreviated to n-, e.g. n-butane for CH3CH2CH2CH3. A compound that contains the (CH3)2CH- group is called iso, which... 

In some heterocyclic ring compounds having the nitrogen in a ring with a CH3 group attached to it, a band near 1050 cm" appears, indicative of the CH3—N structure. 

Tables III and IV list another series of compounds which have CH3—N groups. These compounds have more than one CH3 on the N atom and should be considered separately from the compounds in Table II since more vibrations will be found for the bends. We shall not discuss the assignments in detail however, the general range in which N—CH3 groups can be expected to appear is listed in the last row of the table. This spectral-range summary should be considered general. For more specific assignments, the assignments for the compounds listed in Tables II, III, and IV should be ex-...

The C N group in a ring does not give bands which interfere with the CH3 scissors vibrations although the scissors vibrations appear weak relative to the other bands in the spectrum. 

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