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V. A. IZMAIL’SKII and V. A. GLUSHENKOV
ABSORPTION SPECTRA OF DIPHENYLMETHANE AND DIPHENYLETHANE DERIVATIVES CONTAINING NITRO AND AMINO GROUPS IN DIFFERENT RINGS
(Presented by Academician B. A. Kazanskii, March 21, 1961)
We undertook a study of the absorption spectra of compounds constructed according to the scheme \( \mathrm{O_2N\Phi(CH_2)_n\Phi A} \). The spectra were measured for derivatives of \(n\)-\(\mathrm{NO_2}\)-diphenylmethane (\(n\)-\(\mathrm{NO_2}\)-DPM) (I) and \(n\)-\(\mathrm{NO_2}\)-diphenylethane (\(n\)-\(\mathrm{NO_2}\)-DPE) (II), in which the electron-donor chromophoric component \(A_2\)-H is \(\mathrm{NHCOCH_3}\), \(\mathrm{OH}\), \(\mathrm{NH_2}\), \(\mathrm{NMe_2}\)* (for the color, see Table 1). Compounds (II) were obtained analogously to (1) \((^{1})\).
\[ \mathrm{O_2N{-}\Phi_a{-}CH_2{-}\Phi_b{-}A} \tag{I} \]
\[ \mathrm{O_2N{-}\Phi_a{-}CH_2CH_2{-}\Phi_b{-}A} \tag{II} \]
\[ \mathrm{O_2N{-}\Phi_a{-}CH_2{-}\Phi_b} \tag{III} \]
\[ \text{spatial scheme for } \mathrm{O_2N{-}\Phi_a{-}CH_2{-}\Phi_b{-}A} \tag{IV**} \]
Analysis of the spectra of the \(n\)-\(\mathrm{NO_2}\)-DPM compounds (I) was carried out from the standpoint of the theory of inductively interacting systems \((^{2,3})\), developed for analyzing the spectra of diphenylamine derivatives of the structure \(4\)-\(\mathrm{O_2N\Phi NH\Phi A}\)-\(4'\).
In derivatives of \(4\)-\(\mathrm{NO_2}\)-diphenylamine the main chromophoric system is the system \(\mathrm{BKA'O_2N\Phi NH}\); in derivatives of \(n\)-\(\mathrm{NO_2}\)-DPM and \(n\)-\(\mathrm{NO_2}\)-DPE the main chromophoric system should be the system \(\mathrm{BKA'}\, n\)-\(\mathrm{O_2N\Phi CH_2}\) (IV), the state of which is modified by inductive interaction with the system \(\mathrm{KA^2}\). The validity of this approach is confirmed by the fact that in the spectra of (I) and (II) we find bands of the systems of both rings: ring \(a\), \(\mathrm{BKA'}\) (bands \(I^a\) and \(II^a\)) and ring \(b\), \(\mathrm{KA^2}\), more precisely \(\mathrm{A'KA^2}\) (bands \(I^b\) and \(II^b\)), Table 1.
Upon introduction of phenyl into \(\mathrm{O_2N\Phi CH_3}\) (No. 1) we observe a displacement of band \(I^a\) by \(+3\) mμ, and of band \(II^a\) by \(+10\) mμ. Bands \(I^a\) and \(II^a\), relative to the calculated sum of the extinctions of the systems of rings \(a\) and \(b\) (No. 4), are also shifted bathochromically by \(+3\) mμ and \(+10\) mμ, respectively, but the absorption limit at \(\lg \varepsilon = 1\) is shifted by \(+15\) mμ (Nos. 1–4, Table 1, Fig. 1). In agreement with \((^{3,5})\), we regard this effect as a consequence of increased polarization in the ground state of the \(\mathrm{BKA'}\,\mathrm{O_2N\Phi CH_2}\) system: as a result of mutual induction, in (III) there arises \(\delta-\), which enhances \(\Delta+\) in comparison with \(\Delta+\) in the initial \(\mathrm{O_2N\Phi CH_3}\). The correctness of this approach is confirmed: 1) by the fact that the curve of \(\mathrm{O_2N\Phi CH_2CH_2\Phi}\) (No. 5) almost coincides with curve (No. 1) in Fig. 2: replacement of the \(\mathrm{CH_2}\) group by the \(\mathrm{CH_2CH_2}\) group leads to a fall in the polarization of ring \(b\), to a decrease in inductive interaction, and to the approach of the spectrum to the calculated one (Nos. 4–5); 2) by the fact that a shift toward longer wavelengths occurs upon introduction into (I) and (II) of \(A^2 = \mathrm{NH_2}, \mathrm{NMe_2}\).
Under the influence of \(A^2\), a larger charge \(\delta' -\) should arise in (I) than \(\delta-\) in (III), which in turn should intensify the polarization in \(\mathrm{BKA'}\)
* \(\Phi = n\)-phenylene — \(\mathrm{C_6H_4}\); at the end of the chain — \(\mathrm{C_6H_5}\); \(\mathrm{Me} = \mathrm{CH_3}\); \(n = 1, 2\).
** Construction of scheme (IV) with allowance for standard dimensions shows the presence of spatial factors preventing coplanarity of the benzene rings \(a\) and \(b\): according to \((^{4})\) they are rotated by \(52^\circ\); the angle of the vectors of \(a\) and \(b\) is \(120^\circ\).
Table 1*
| No. | Compound (m.p. and color) | Solvent** | Bands of nucleus b: Ib λmax | Ib εmax | Bands of nucleus b: IIb λmax | IIb εmax | Bands of nucleus a: Ia λmax | Ia εmax | Bands of nucleus a: IIa λmax | IIa εmax | Exoband λmax | Exoband εmax | Absorption edge at lg ε = 1 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | O₂NΦCH₃ | C | — | — | — | — | 274 | 10850 | ∼320 | 830 | — | — | 385 |
| 2 | O₂NΦCH₃ | C | — | — | — | — | 277 | 10600 | ∼330 | 820 | — | — | 400 |
| 2a | O₂NΦCH₂Φ | B | — | — | — | — | 277 | 10400 | ∼330 | 500 | — | — | 385 |
| 2b | 31°, colorless | G | — | — | — | — | 267 | 11300 | ∼310 | 330 | — | — | 385 |
| 3 | H₃CΦ | C | — | — | 255 | 360 | — | — | — | — | — | — | — |
| 3 | H₃CΦ | C | — | — | 262 | 340 | — | — | — | — | — | — | — |
| 4 | (O₂NΦCH₃ + H₃CΦ) calc. | C | — | — | — | — | 274 | 10800 | ∼320 | 830 | — | — | 385 |
| 5 | O₂NΦCH₂CH₂Φ | C | — | — | — | — | 277 | 8200 | ∼330 | 450 | — | — | 385 |
| 5a | 70–71°, colorless | G | — | — | — | — | 267 | 14000 | ∼370 | 470 | — | — | — |
| 6 | O₂NΦCH₂ΦNH₂ | C | 235 | 11600 | — | — | 275 | 9200 | ∼330 | 1530 | ∼420 | 40 | 440 |
| 6a | 98°, orange-yellow | B | — | — | — | — | 275 | 8100 | ∼320 | 1760 | ∼420 | 20 | 435 |
| 6b | 98°, orange-yellow | G | 230 | 9680 | — | — | 255 | 14700 | ∼320 | 1700 | — | — | 400 |
| 7 | H₃CΦNH₂ | C | 235 | 11700 | 290 | 1800 | — | — | — | — | — | — | — |
| 8 | (O₂NΦCH₃ + H₃CΦNH₂) calc. | C | 235 | 15900 | — | — | 274 | 11800 | ∼320 | 900 | — | — | 385 |
| 9 | O₂NΦCH₂ΦNH₂ | A, 10⁻² | — | — | — | — | — | — | 330 | 2640 | ∼420 | 140 | 490 |
| 10 | O₂NΦCH₂CH₂·ΦNH₂ | C | 235 | 12800 | — | — | 275 | 13400 | ∼330 | 1100 | 420 | 135 | 475 |
| 10a | 138°, yellow-orange | G | — | — | — | — | 255 | 19200 | ∼330 | 730 | ∼400 | 130 | 437 |
| 11 | O₂NΦCH₂CH₂·ΦNH₂ | A, 10⁻² | — | — | — | — | — | — | ∼330 | 2700 | ∼420 | 270 | 508 |
| 12 | O₂NΦCH₂ΦNMe₂ | C | 265 | 25200 | — | — | ∼270 | 20000 | ∼340 | 2235 | ∼420 | 190 | 480 |
| 12a | 87°, yellow-orange | B | — | — | — | — | ∼270 | 18900 | ∼340 | 1600 | ∼420 | 100 | 438 |
| 12b | 87°, yellow-orange | G | 262 | 25700 | ∼302 | 4000 | — | — | ∼340 | 1600 | — | — | 409 |
| 13 | H₃CΦNMe₂ | C | 252 | 13300 | 302 | 1900 | — | — | — | — | — | — | — |
| 14 | O₂NΦCH₂ΦNMe₂ | DMA | — | — | — | — | — | — | ∼340 | 3400 | ∼420 | 670 | 500 |
| 15 | (O₂NΦCH₃ + H₃CΦNMe₂) calc. | C | 252 | 19000 | — | — | ∼270 | 13900 | ∼330 | 800 | — | — | 385 |
| 16 | O₂NΦCH₂·CH₂ΦNMe₂ | C | 260 | 19500 | — | — | ∼275 | 14400 | ∼340 | 1100 | 430 | 250 | 515 |
| 16 | O₂NΦCH₂·CH₂ΦNMe₂ | G | 260 | 20600 | ∼302 | 3480 | — | — | ∼340 | 750 | ∼400 | 170 | 504 |
| 16a | 147°, yellow-orange | DMA | — | — | — | — | — | — | ∼340 | 3400 | 430 | 830 | 530 |
| 17 | 147°, yellow-orange |
* The numbers of the compounds and solutions in Table 1 correspond to the numbers in the text and in the figures. The concentration of the solutions is \(10^{-4}\) mol/l.
* C = alcohol, B = benzene, G = n*-hexane, A = aniline, DMA = dimethylaniline.
\((\Delta' + > \Delta +)\), and, according to the rule relating the bathochromic effect to the degree of electron displacements in the ground state \((^{2,5,6})\), the spectrum should shift to the red. The influence of \(A^2 — \mathrm{NH_2}\) in No. 6 (I) on \(\lambda_{\max}^{II^a}\) is still not large: \(\lambda_{\max}^{II^a}\) remained at ∼330 mμ, but \(\varepsilon_{\max}^{II^a}\) increased to 1530 (Nos. 1, 2, 6). However, for No. 6 a strong bathochromic displacement of the absorption boundary is observed: at \(\lg \varepsilon = 1\), \(+40\) and \(+55\) mμ (in comparison with No. 2 and No. 1, Fig. 1), and a new band at ∼420 mμ appears in the form of an inflection. It is a consequence not of endomolecular, but of exomolecular interactions of the external field of the electrophilic system \(BKA'O_2N\Phi CH_2\) with the electron-donor system \(A'KA^2CH_2\Phi NH_2\) (IV), with formation of a donor–acceptor complex as a result of association (see the analogous association \((^7)\)).
The presence of exomolecular interaction in solution No. 6 is confirmed by the observed increase in the bathochromic displacement of the spectral curve in the region of the exoband: 1) when the concentration is increased from \(C = 10^{-4}\) to \(C = 10^{-2}\) mol/l; 2) on going from \(CH_2\) to \(CH_2CH_2\), i.e., to the DPE derivative No. 10; 3) when an excess of the \(A'KA^2\) component is added to the alcoholic solution in the form of \(CH_3\Phi NH_2\) or \(C_6H_5NH_2\) (No. 9, Fig. 1, Table 1); 4) for spectrum No. 10 in aniline (No. 11, Fig. 1). This conclusion is confirmed by the considerably stronger endo- and exo-effect for (I, \(A^2 = \mathrm{NMe_2}\)). Since \(\mathrm{NMe_2}\) is stronger than \(\mathrm{NH_2}\) (No. 12, Table 1, Fig. 2), band \(II^a\) shifted bathochromically by \(+10\) mμ and considerably
increased, while for the exopole the shift of the absorption edge at \(\lg \varepsilon = 1\) is already \(+95\) and \(+80\) m\(\mu\) relative to Nos. 1 and 2. That this effect is a consequence of the appearance of an exopole as a result of exomolecular interactions of the type of interaction in donor–acceptor complexes of nitrotel with arylamines is demonstrated by: the presence in Nos. 12 and
Fig. 1
Fig. 2
14 of stronger shifts than in Nos. 6 and 9 and in comparison with the spectrum of No. 15, calculated for the sum of the components \((\mathrm{O_2N\Phi CH_3 + CH_3\Phi NMe_2})\); the appearance, for the DPE derivative \((\mathrm{II}, A^2 — \mathrm{NMe_2})\), of a clearly expressed maximum of the exopole \(\lambda_{\max}^{\mathrm{exo}} = 430\) m\(\mu\) \((\varepsilon = 250)\), despite the low concentration \(C = 10^{-4}\) M/l, and, finally, by an increase of \(\varepsilon_{\max}\) of the exopole to 800 (Fig. 2) with a shift of the absorption edge at \(\lg \varepsilon = 1\) to \(+130\) m\(\mu\) and \(+145\) m\(\mu\) relative to Nos. 2 and 1 (Table 1) for solution No. 17 in \(\mathrm{C_6H_5NMe_2}\) (i.e., when using component \(\overline{K}A_2\) in excess to shift the equilibrium toward a higher concentration of the complex).
We see (Table 1, Fig. 3) that in the spectrum of No. 12, O₂NΦCH₂ΦNMe₂, in the region of bands Iᵃ and IIᵃ there is a considerable deviation from curve No. 15, calculated for the sum of the components, and an even greater deviation from Nos. 1 and 2, which indicates a significant effect of endomolecular mutual influences of the NMe₂ and NO₂ groups: \(\lambda^{16}_{\max}\) for No. 15 (252 mµ) is shifted to the red by \(+13\) mµ, with a considerable increase in \(\varepsilon\) from 19000 to 25200. For No. 16 this effect decreases (\(\Delta\lambda + 8\) mµ and \(\varepsilon_{\max}\) 19500), i.e., in No. 16 the endomolecular interactions weaken: as a result of the greater separation of the charges \(\Delta' +\) from \(\delta' -\) in (II), the polarization of the nucleus \(a\) system decreases.
Fig. 3
Since in \(n\)-NO₂-DPM the planes of both nuclei \(a\) and \(b\) are rotated by 52° (⁴), the conditions for conjugation of the nuclei by means of CH₂ are disturbed. As a result, the CH₂ group can interact, depending on the rotation of the benzene nuclei, now with nucleus \(a\), now with nucleus \(b\). This may be explained by the existence of two rotational states (conformations) and may be represented by schemes (Va) and (Vb) with different positions of conjugation of CH₂ with one of the two nuclei \(a\) or \(b\) (\(\sigma,\pi\)-conjugation). Owing to the polar opposition of NO₂ and CH₂, position (Va)
\[ \mathrm{O_2N{-}\langle a\rangle{-}CH_2{-}\langle b\rangle{-}A^2} \tag{Va} \]
\[ \mathrm{O_2N{-}\langle a\rangle{-}CH_2{-}\langle b\rangle{-}A^2} \tag{Vb} \]
is more favorable (a larger value of the conjugation energy) and therefore predominates.
Laboratory of Dye Chemistry and the Problem of Color
at the V. I. Lenin Moscow State Pedagogical Institute
Received
21 III 1961
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