CHEMISTRY

V. A. IZMAILSKII, Yu. A. FEDOROV

GENETICS OF THE SPECTRA OF DERIVATIVES OF BENZYLIDENEANILINE AND BENZYLIDENE-1-NAPHTHYLAMINE CONTAINING NO₂ AND NMe₂ GROUPS

(Presented by Academician A. N. Terenin, March 23, 1964)

Izmailskii and Smirnov (¹) pointed out that, in discussing the spectra of benzylideneaniline (BA) and its derivatives (I) and (II), two types of participation of CH = N in conjugation should be taken into account: by means of the π-electrons of the double bond and by means of the free doublet of the N atom. In the latter case the coplanarity of nuclei a and b is disturbed. This was confirmed by the fact that in the case (II, B = NO₂) bands of the H₂NΦNO₂ system are observed.

K — the entire conjugated system; K_b — the conjugated system of nucleus b with a substituent and the CH = N group (the K_b band); K_a — bands of the system of the aniline nucleus a with a substituent; B = H, NO₂; A = H, NMe₂, OH, OCH₃.

In analyzing the spectra, account was taken of the possibility of manifestation in the spectrum of a band of a single conjugated system of the stilbene type (K-band) (Fig. 4 (¹); Fig. 13 (²)) and of bands of partial conjugated systems: nucleus b with CH = N (K_b — band of the XC₆H₅CH = N system) and nucleus a with the N atom of the CH = N group (K_a — band) (I, II)*. The same hypothesis was put forward by Ebara (³), without mentioning priority (¹), and with erroneous spectroscopic data**. Brocklehurst (⁴) confirmed the idea of noncoplanarity (¹) and gave an interpretation of the spectral bands of BA at ~312 and 256 mμ. He assigned the 256 mμ band to the K_b system, comparing it with C₆H₅CH=NMe (λ_max 246 mμ). The presence of the K_a band of the aniline =NC₆H₅ system has been observed (³, ⁵).

We undertook to check these conclusions on a series of BA and benzylidene-1-naphthylamine (BNph) derivatives (III) and (IV), and, in order to eliminate possible decomposition in alcohol (¹) of derivatives (II, IV, B = NO₂), we investigated the spectra in dichloroethane (DCE).

* In the present work we have used simplified designations of the chromophoric systems K, K_a, and K_b, without indicating all the constituent parts of the chromophoric system (BKA, BK, AK, etc.), as is customary in our papers.

** Ebara did not take into account the decomposition of compounds (II, B = NO₂) in alcohol (¹) and even in mixtures of alcohol and conc. HCl. As a result, the conclusions lack an experimental basis and are sometimes clearly erroneous.

Table 1

Spectra of compounds in 1,2-dichloroethane, \(C=10^{-4}\) mol/l

\(^{1}\) The numbers of the compounds in Table 1 correspond to the numbers in the figures.
\(^{2}\) Classification of the bands of the \(a\) nucleus according to [11].
\(^{3}\) Classification of the bands of Nph derivatives (Nos. 13–28) and anthracene (Antr) derivatives (Nos. 29–32) according to [9].
\(^{4}\) Superposition of bands.
\(^{5}\) Antr = \(\alpha\)-anthranyl.

In the spectrum of BNph (IV, \(A=B=H\), Table 1, No. 13) four bands were found: the K-band \(\lambda_{\max}=347\) mµ; the small \(\varepsilon\) (8400) is caused by violation of coplanarity; the \(K_b\)-band at 257 mµ of the \(\Phi\mathrm{CH=N}\) system; and the bands of the \(K_a\) system at 290 and 233 mµ—both bands of the \(\alpha\)-naphthylamine system, shifted toward the UV because of replacement of the \(\mathrm{H_2N}\) group by the \(\mathrm{CH=N}\) group and partial disturbance of conjugation of the N atom with the Nph nucleus.

Spectra of \(\Phi\mathrm{CH=NArNO_2}\). Upon introduction into BA of the strong electron-acceptor group \(\mathrm{NO_2}\) in the \(n\)-position to the N atom of nucleus \(a\), conjugation of the N-atom doublet is enhanced. The \(K_a\) band at 322 mµ of BA-\(\mathrm{NO_2}\)-4 is a hypsochromically shifted band of the \(n\)-\(\mathrm{NO_2}\)-aniline system (Nos. 3, 4, Fig. 1, Table 1). Even a \(\chi'\)-band is observed

Fig. 1

~226 mµ, typical for cochromophores of the BKA type (⁶). The angle of rotation of ring a with respect to ring b should approach 90°. However, the increase in ε (Δε 2800) in comparison with 4-NO₂-aniline indicates the possibility of superposition of a stilbene-type K band (4-NO₂-stilbene 350 mµ). The hypsochromic shift of the λ_max band of the O₂NΦNH₂ system (Δλ = −18 mµ) is explained by replacement of the H₂N group by CH=N. The K_b band (O₂NΦCH=N) is overlapped.

Fig. 2

Similarly, for BNph-NO₂-4 (No. 15), λ_max = 380 mµ is a hypsochromically shifted band of 4-nitro-1-naphthylamine (Δλ = −22 mµ). The 262 mµ band belongs mainly to ring b (probably with some superposition of the β-band of NO₂NphNH₂-1,4, 257 mµ) (Fig. 1, Nos. 15, 16, 2). This is confirmed by the observation that in O₂NΦCH=NNphNO₂-1,4 (No. 20) the 262 mµ band is shifted to 282 mµ, which is close to 285 mµ for O₂NΦCH=NCH₃ (No. 6, Table 1). Such a shift would not have been observed if the 262 mµ band belonged to ring a. The 230 mµ band belongs to the naphthalene system.

Spectra of O₂NΦCH=NArX. The concept of disturbance of coplanarity (¹) and the possibility of manifestation of three quasiautonomous systems is also confirmed for derivatives of types (I, B = NO₂, A = H) and (III, B = NO₂, A = H), as well as in the presence in them of an additional 4-NMe₂ group in ring a. In all compounds 5, 17 and 7, 18 we find a K band and also a K_b band corresponding to the O₂NΦCH=N system (No. 6) (Fig. 2, Table 1). The system of ring b thus reveals its quasiautonomy, which is a consequence of the absence of coplanarity. In the naphthalene 4-nitrobenzylidene derivatives the β-bands of the amino system of ring a* are also clearly visible: for No. 17 (III, B = NO₂, A = H) 230 mµ (ε = 45,300) (Fig. 2, Table 1). For No. 18 (III, B = NO₂, A = NMe₂) the band 257 mµ (ε = 18,000) is very close to the band 255 mµ (ε = 16,900) of N,N-dimethylnaphthylenediamine-1,4 (No. 19).

Spectra of 4′-Me₂NΦCH=NArX. The high intensity of the K bands of 4′-Me₂NBA and 4′-Me₂NBNph (Table 1, Nos. 10, 22) (ε = 35,300, 30,500) indicates their genetic relationship with the K band of 4-Me₂NΦCH=NCH₃ (λ_max = 305 mµ, ε = 24,000). The increase in ε simultaneously with λ_max from 305 to 355 and 367 mµ is a consequence of addition to the conjugated

* In the translation (¹²) of article (¹¹), the term “quasiautonomous” was translated incorrectly: instead of quasiautonomic, quasiatomic was given.

system of the benzene or naphthalene nucleus and by approximation to the system \(4\text{-}\mathrm{Me}_2\mathrm{N}\Phi\mathrm{CH}=\mathrm{CH}\Phi\). Complete coplanarity, however, is absent, as is evident from the presence of the \(K_b\) band, which appears in the \(\lg \varepsilon(\lambda)\) curve as an inflection in the region of 320 mµ, and also of the \(K_a\) band of the system \(=\mathrm{NC}_6\mathrm{H}_5\) (240 mµ) (Table 1, Nos. 10, 10a). When \(4\text{-}\mathrm{NO}_2\) is added to nucleus \(a\), as might be expected, a considerable further bathochromic shift of the K band is observed to 405 (No. 12) and 425 mµ (No. 24); however, \(\varepsilon\) in both cases decreases somewhat (Table 1), and, in addition, bands appear in the region of 312 (No. 12), 322 and 342 mµ (No. 24), which we regard as bands of the \(K_b\) system with superposition of the system of nucleus \(a\). This indicates that in both cases there are deviations from coplanarity.

Spectra of \(\mathrm{X}\Phi\mathrm{CH}=\mathrm{NArNMe}_2\). Of considerable theoretical interest is the observation \({}^{1}\) that \(\mathrm{NMe}_2\) in nucleus \(a\) on the side of the N atom in BA produces a substantially larger bathochromic effect than in nucleus \(b\): in BA-\(\mathrm{NMe}_2\)-4 and BNph-\(\mathrm{NMe}_2\)-4 (Nos. 9, 21) \(\lambda_{\max}\) is 375 and 380 mµ; for \(4'\text{-}\mathrm{Me}_2\mathrm{N}\)-BA and \(4'\text{-}\mathrm{Me}_2\mathrm{N}\)-BNph (Nos. 10, 22) \(\lambda_{\max}\) is 355 and 367 mµ (Table 1). The \(4\text{-}\mathrm{NMe}_2\) group creates a \(\delta^-\) charge on the carbon of nucleus \(c\) bonded to the N atom of the \(\mathrm{CH}=\mathrm{N}\) group and thereby reduces the capacity of the N-atom doublet for conjugation with nucleus \(a\) and promotes the formation of a more coplanar conjugated K system of the type \(4\text{-}\mathrm{Me}_2\mathrm{N}\Phi\mathrm{CH}=\mathrm{CH}\Phi\) (\(\lambda_{\max}\) 340 mµ, \(\varepsilon\) 29 500 in alcohol). That the disturbance of coplanarity in No. 9 is nevertheless considerable is evident from the small value of \(\varepsilon\), 18 250, and also from the presence of bands of the \(K_b\) and \(K_a\) components. As a result of steric hindrance and the withdrawal of \(4\text{-}\mathrm{NMe}_2\) from the plane of the naphthalene nucleus, the intensity of the K band for BNph-\(\mathrm{NMe}_2\)-4 (No. 21) is greatly reduced, \(\varepsilon = 11\,600\) instead of 18 250 for No. 9. An analogous decrease in \(\lambda_{\max}\) and \(\varepsilon_{\max}\) of the K band as a consequence of steric hindrance is found for No. 18 in comparison with No. 7 (Fig. 2, Table 1).

The explanation set forth for the stronger influence on the magnitude of the shift of \(\lambda_{\max}\) of \(\mathrm{NMe}_2\) in nucleus \(a\) than in \(b\) differs from Smith’s explanation \({}^{10}\), based on LCAO-MO calculations, by transitions to an excited state associated with electron migration toward the structures

\[ \Phi-\overline{\mathrm{CH}}-\mathrm{N}= \begin{matrix} \large\hexagon \end{matrix} + \]

and

\[ -\begin{matrix} \large\hexagon \end{matrix} =\mathrm{CH}-\mathrm{N}= \begin{matrix} \large\hexagon \end{matrix} + . \]

The author did not take into account that the transition to the excited state depends not so much on the microstructure of the initial BA system as on the ground state and the steric conditions in the microstructure of the substituted derivative. The substituent may introduce changes into the electron distribution in the ground and excited states. Our investigations provide an approach to explaining the genetics of the spectra from the standpoint of the possibility of manifestation in the spectra of separate quasi-autonomous chromophoric systems connected with different conditions for electron migration upon transition to the excited state.

Laboratory of Dye Chemistry and Problems of Color
at the V. I. Lenin Moscow State Pedagogical Institute

Received
20 III 1964

CITED LITERATURE

1. V. A. Izmail’skii, E. A. Smirnov, ZhOKh, 26, 3042 (1956).
2. V. A. Izmail’skii, Khim. nauka i prom., 3, No. 2, 243, 245 (1960).
3. N. Ebara, Bull. Chem. Soc. Japan, 33, No. 4, 534 (1960).
4. P. Brocklehurst, Tetrahedron, 18, 299 (1962).
5. J. Schulze et al., Helv., 44, 428 (1961).
6. W. Kumler, J. Am. Chem. Soc., 68, 1184 (1946).
7. G. Grammatikakis, Bull. Soc. chim. France, 1951, 534.
8. M. Calvin, H. W. Alter, J. Chem. Phys., 19, 765 (1951).
9. E. Clar, Aromatische Kohlenwasserstoffe, Berlin, 1952.
10. W. F. Smith, Tetrahedron, 19, 445 (1963).
11. E. E. Milliaresi, V. A. Izmail’skii, DAN, 146, No. 5, 1094 (1962).
12. E. M. Milliaresi, V. Izmailskii, Proc. Acad. of Sci. USSR in English translation, 146, No. 1–6, 894 (1963). Consultants Bureau, N. Y.