Overtone aromatic amines

NIR spectrophotometry in the region from 8000 to 4000 cm-1 was used to measure the kinetics of copolymerization of an aromatic bismaleimide (72) derived from an aromatic diamine (e.g. 5a), taking place at 160 to 180 °C. The following NIR spectral ranges were useful for this study primary amine first overtones (vn h) at 7000 to 6400 cm-1, double bond first overtone (vc=c-h) at 6100 cm-1, aromatic first overtones (vc-h) at 6000 to 5750 cm-1, aliphatic first overtones (vc-h) at 5750 to 5350 cm-1 and primary aromatic amine combination bands first overtones (vn h + <5nh2) at 5150 to 4800 cm-1. The process consisted mainly of a second-order Michael addition, as depicted in equation 14, and not the plausible imide opening to yield a maleic dianilide (119), as shown in equation 15. A Michael addition between maleimide moieties and secondary amine moieties present in the products (118) also takes place, however at a rate of about one fourth of that of the primary amine moieties. To improve the SNR of the measurements, usually the results of... 

Investigated systems include a broad variety of dissolved organometallic species, electrochemically active organic molecules and redox active polymers like polyani-line (for a review, see [142]). Both dissolved species and species attached by adsorption, covalent bonding or film-forming deposition have been studied. Dissolved poly aniline dispersions as prepared by chemical oxidation [145] show various transitions in the NIR, as depicted in a set of NIR spectra in Fig. 5.40. The bands around X = 1490 nm and 1950 nm are overtones of the N-H stretch mode of an aromatic amine, whereas the band around X = 2300 nm is caused by the oligomer itself, which presumably indicates the presence of mobile charge carriers. 

As in the case of the aliphatic amines, secondary aromatic amines show only one NH-stretching overtone. For A-butyl aniline in CCI4, for example, the overtone is at 6675 cm" (1498 nm). The effects of hydrogen bonding on the mechanical anharmonicity of the NH-stretching vibration of N-methylaniline have been reported."... 

In heterocyclic aromatic amines such as pyrrols, indoles, and carbazoles, Ihoe is a first overtone NH-stretching between 6803 cm (1470 nm) and 6897 cm" (1440 nm)." Unlike the aliphatic amines, where the intensity of the overtone is approximately the same as the intensity of the fundamental, the aromatic and heterocyclic amines have a much greater absorptivity difference between fundamental and overtone. The overtone intensities do not vary widely, but the intensities of the fundamentals vary by a factor of about 100 from aliphatic to heterocyclic. Table 8.1 lists some of the intensities, given in integrated peak area. 

Table 8.2 lists band positions and intensities of some primary aromatic amines in carbon tetrachloride, illustrating the effect of substituents. The table also includes the second overtone... 

N-H (2v) symmetric, primary aromatic amine in CCI4 as para-NH2 grouping N-H (2v),. CONH2 N-H (2v) stretching bonded NH, disordered phase from polyamide 11 N-H (2v),. CONH2 N-H (2v), secondary amine as (R-NH-R), dimethylamine (vapor), first overtone band intensity comparisons, CCI4 solution C-H, methyne (1-hexyne) as (R-C-C=C-H)... 

Finally, in the second overtone region only very weak bands can be observed for aromatic amines, the most outstanding being the symmetric band at about 9800 cm, of hmited analytical value . 

Mixtures of N-alkyl aromatic amines and N-alkyl-N-hy-droxyalkyl aromatic amines using the 1.5-/i first overtone of the NH stretching absorption and the first overtone of OH at 1.4 n. Beer s law was not followed for CCU solutions at 1.4 g due to H bonding through the OH group Mixtures of aniline and N-ethyl aniline (up to 99% of either) in CCU solution at 10 cm thickness, using 1.972 /i for aniline and 1.493 n for N-ethylaniline (aniline interference at the latter wavelength was considerable). Both followed Beer s... 

Near-infrared spectrometry is a valuable tool for analyzing mixtures of aromatic amines. Primary aromatic amines are characterized by two relatively intense absorption bands near 1.97 and 1.49 pm. The band at 1.97 pm is a combination ofN—H bending and stretching modes, and the one at 1.49 pm is the first overtone of the symmetric N—H stretching vibration. Secondary amines exhibit an overtone band, but they do not absorb appreciably in the combination region. Secondary amines exhibit an overtone band, but they do... 

There is some correlation between molecular structure and band position for certain bands, but because these are often overtone and combination bands, their positions are not as structure-dependent as the fundamental bands in the mid-IR. For example, primary amines, both ahphatic and aromatic, have two absorption bands, one at about 1500 nm and the second at about 1990 nm. Secondary amines have only one band at about 1500 nm. As expected, a tertiary amine has no NH band. Amides with an — NH2 group can be distinguished from R— NH—R amides by the number and position of the N—H bands. The reference by Goddu has a detailed table of NIR structure-wavelength correlations. 

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