Research in the Chemistry of Carbazole Derivatives
Abstract Generated abstract
This study examines the coordination behavior of 9-acetylcarbazole and 3-acetylcarbazole in complexes with aluminum chloride, with and without hydrogen chloride, as part of work on the rearrangement of 9-acetylcarbazole to 3-acetylcarbazole. Infrared spectra measured in methylene chloride were compared for the free compounds and their complexes, focusing on changes in N-C, N-H, and carbonyl absorption bands. The spectra indicate that complex formation is associated with new intense absorption bands involving the nitrogen-containing carbazole nucleus, while carbonyl frequencies remain essentially unchanged. The authors conclude that the donor center in both acetylcarbazoles is the nitrogen atom rather than the acetyl carbonyl oxygen, and that interaction with aluminum chloride and hydrogen chloride probably involves protonation at nitrogen.
Full Text
Research in the Chemistry of Carbazole Derivatives
72. On the Structure of Complexes of Certain Acetyl Derivatives of Carbazole with Aluminum Chloride
V. L. Ivasenko, Yu. G. Yur’ev, E. E. Sirotkina, V. P. Lopatinskii
(Presented by the Scientific-Methodological Seminar of the Faculty of Chemical Technology)
In the course of studies carried out to clarify certain features of the mechanism of the rearrangement of 9-acetylcarbazole into 3-acetylcarbazole, the method of IR spectroscopy was used to determine the center of donor activity of acetyl derivatives of carbazole. IR spectra were recorded for the following two systems:
Group I — 9-acetylcarbazole, 9-acetylcarbazole with aluminum chloride, 9-acetylcarbazole with aluminum chloride and hydrogen chloride.
Group II — 3-acetylcarbazole, 3-acetylcarbazole with aluminum chloride, 3-acetylcarbazole with aluminum chloride and hydrogen chloride.
All measurements were carried out in methylene chloride solution on an IKS-14 spectrophotometer (prisms: NaCl, LiF; CaF₂ cells) at a temperature of 20°C (±1°). The concentration of donors was \(2 \cdot 10^{-1}\) M; the layer thickness was 0.124 mm.
Comparison of the IR spectra of the compounds of group I shows (Tables 1 and 2) that the absorption band of the unbound N—C groups lies in the region
Table 1
| Substance | \(\nu_{\max}\) N—C (cm\(^{-1}\)) | Intensity of the N—C absorption band, relative units |
|---|---|---|
| 9-acetylcarbazole | 2984—3104 | 0.32 |
| 9-acetylcarbazole with aluminum chloride | 2984—3550 | 0.95 |
| 9-acetylcarbazole with aluminum chloride and hydrogen chloride | 2984—3550 | 0.94 |
2984—3104 cm\(^{-1}\). Formation of the complex leads to the appearance of a new strong absorption band with the frequency of bound N—C groups, 3450 cm\(^{-1}\), which is approximately three times greater in intensity than the absorption band of the unbound N—C group.
The position and intensity of the stretching vibrations of the carbonyl group of 9-acetylcarbazole with aluminum chloride and hydrogen chloride do not change (Table 2).
Thus, the coordination center in the donor molecule is the nitrogen atom, and not the carbonyl oxygen of the acetyl group (1).
Table 2
| Substance | $\nu_{\max}\ \mathrm{C{=}O}\ (cm^{-1})$ | Intensity of the $\mathrm{C{=}O}$ absorption band, relative units |
|---|---|---|
| 9-Acetylcarbazole | 1682—1705 | 0.9 |
| 9-Acetylcarbazole with aluminum chloride | 1682—1705 | 0.9 |
| 9-Acetylcarbazole with aluminum chloride and hydrogen chloride | 1698—1705 | 0.91 |
When considering the IR spectra of compounds of group II (Table 3), it was found that in the molecule of 3-acetylcarbazole the N—H absorption band lies in the frequency region of 3449 $cm^{-1}$. Upon interaction of 3-acetylcarbazole with aluminum chloride and hydrogen chloride, in addition to it there appears a new, intense and broad absorption band in the region 3000—3300 $cm^{-1}$. This is a direct consequence of the decrease in the force constants of the N—H bond, which is caused by the transfer of electrons from the donor of the amino group to aluminum chloride.
Table 3
| Substance | $\nu_{\max}\ \mathrm{NH}$ free $(cm^{-1})$ | $\nu_{\max}\ \mathrm{N—H}$ bonded $(cm^{-1})$ |
|---|---|---|
| 3-Acetylcarbazole | 3449 | — |
| 3-Acetylcarbazole with aluminum chloride | 3449 | 3000—3300 |
| 3-Acetylcarbazole with aluminum chloride and hydrogen chloride | 3449 | 3000—3300 |
Noteworthy is the fact (Table 4) that upon formation of the complex of 3-acetylcarbazole with aluminum chloride and hydrogen chloride, the intensity of the carbonyl group changes insignificantly, while the frequency remains constant, which can apparently be explained by the sensitivity of the carbonyl group to various kinds of changes in the molecule (2, 3).
Table 4
| Substance | $\nu_{\max}\ \mathrm{C{=}O}\ (cm^{-1})$ | Intensity of the CO absorption band (relative units) |
|---|---|---|
| 3-Acetylcarbazole | 1682 | 0.79 |
| 3-Acetylcarbazole with aluminum chloride | 1682 | 0.73 |
| 3-Acetylcarbazole with aluminum chloride and hydrogen chloride | 1682 | 0.68 |
Conclusions
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It has been established that the center of donor activity of 9-acetylcarbazole and 3-acetylcarbazole in the formation of complexes with aluminum chloride is the nitrogen atom, and not the carbonyl oxygen.
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The formation of the complex compound is accompanied by the appearance of a new, intense absorption band.
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In the interaction of 9-acetylcarbazole and 3-acetylcarbazole with aluminum chloride and hydrogen chloride, the nitrogen atom of the carbazole nucleus is probably protonated.
References
- V. M. Kazakova, Ya. K. Syrkin. Proceedings of the Academy of Sciences of the USSR, Chemical Series, 673, 1958.
- W. West (ed.). The Application of Spectroscopy in Chemistry. Moscow, IL, 1964.
- L. Bellamy. The Infrared Spectra of Complex Molecules. Moscow, IL, 1963.