CHEMISTRY

V. A. GLUSHENKOV and V. A. IZMAILSKII

THE EXO-INTERACTION BAND IN THE SPECTRA OF SALTS OF DIPHENYLALKANES WITH $\mathrm{NO_2}$ AND $\mathrm{OH}$ GROUPS IN DIFFERENT NUCLEI

(Presented by Academician B. A. Kazanskii, 30 IX 1961)

Taking into account that the electron-donor properties and the influence on the spectrum of the phenolate $\overset{\times\times}{\mathrm{O}^{-}}$ in chromophores of the VKA type* are very close to those of the $\mathrm{NMe_2}$ group ($^2$), we suggested, on the basis of a number of our works, for example ($^{3,4}$), that phenolate chromophoric components of the type $\mathrm{C_6H_5O^-}$, $n\text{-}\mathrm{CH_3C_6H_4O^-}$ should form colored complexes of the type [VK...AK], for example $[\mathrm{C_6H_5NO_2}\ldots \mathrm{C_6H_5O^-}]\mathrm{Na^+}$, analogous to $[\mathrm{C_6H_5NO_2}\ldots \mathrm{C_6H_5NMe_2}]$.

Further, proceeding from the fact established by us that the coloration of $\mathrm{NMe_2}$ derivatives of $n$-$\mathrm{NO_2}$-diphenylmethane ($n$-$\mathrm{NO_2}$-DFM) (I, $A^2=\mathrm{NMe_2}$) and $n$-$\mathrm{NO_2}$-diphenylethane ($n$-$\mathrm{NO_2}$-DFE) (II, $A^2=\mathrm{NMe_2}$) is a consequence not of endomolecular (through $\mathrm{CH_2}$ or $\mathrm{CH_2CH_2}$), but of exomolecular interaction of the VK and AK systems ($^5$), it could be expected that compounds of the type $\mathrm{O_2N\Phi}—(\mathrm{CH_2})_n—\mathrm{\Phi OH}$ would form colored salts of the type $[\mathrm{O_2N\Phi}—(\mathrm{CH_2})_n—\mathrm{\Phi O^-}]\mathrm{Na^+}$ as a result of strengthening of the donor group OH upon conversion to $\mathrm{O^-}$ and of manifestation of exo-interaction with formation of a colored complex of structure III or, more probably, IV.

To test this, derivatives of $n$-$\mathrm{NO_2}$-DFM (I) and $n$-$\mathrm{NO_2}$-DFE (II) with $A^2=\mathrm{OH}$ were synthesized, and the spectra of solutions of their salts ($A^2=\mathrm{O^-}$) were compared with the spectrum of a solution of $[\mathrm{O_2N\Phi CH_3}+\mathrm{H_3C\Phi ONa}]$, in which, according to what was stated above, formation of a colored complex $[\mathrm{O_2N\Phi CH_3}\ldots \mathrm{CH_3\Phi O^-}]\mathrm{Na^+}$ could be expected (Figs. 1, 2; the numbers of the curves correspond to the numbers in Table 1).

On addition to solutions No. 1 and No. 8 in alcohol of an equimolecular amount of caustic alkali, the pale-yellow coloration, as we expected, turns yellow. Bands $I^a$ and $II^a$ of the nucleus system $a$, on conversion to the salt, remain in the same place (No. 4 and No. 9); in the UV there appears band $I^b$ of the salt of component $\mathrm{H_3C\Phi ONa}$ (No. 5). The deepening of the color is a consequence of the appearance of a new absorption region—the exo-band $\sim 420$ mμ (Figs. 1, 2), close to the exo-band (II, $A^2=\mathrm{NMe_2}$) ($^5$) $\lambda_{\max} 430$ mμ. For No. 9 II ($A^2=\mathrm{O^-}$) the band appears in the form of a distinct bend, and for No. 7 only in the form of a shoulder ($\varepsilon = 10^3$ at $\lambda \sim 420$ mμ).**

* A conjugated cochromoform system ($^1$), constructed from an electrophilic chromophoric component B (for example $\mathrm{NO_2}$), an electron-donor chromophoric component A (for example $\mathrm{NMe_2}$), and a K-conjugated chromophoric component, for example $n$-$\mathrm{C_6H_4}$— (designation $\Phi$).

** With respect to the properties and spectra of I and II with $A^2=\mathrm{NH_2}$ and $\mathrm{NMe_2}$, one should be guided by ($^{5,6}$), since ($^7$) contains a number of errors.

Table 1

* The numbers of compounds and solutions in Table 1 correspond to the numbers in Figs. 1 and 2. For comparison, see the spectra of the parent compounds (O₂NΦCH₃; O₂NΦCH₂Φ; O₂NΦCH₂CH₂Φ) in the table in [5].

* C — alcohol, Б — benzene, Г — n*-hexane. The NaOH concentration is equimolecular with the corresponding phenol.

That these bands are of the same origin and are a consequence of the exomolecular interaction of the systems of nucleus \(a\) \((\mathrm{BK(A')})\) and nucleus \(b\) \((\mathrm{A'KA^2})\) is confirmed by the following: 1) its position coincides with the exo-band of a solution of the complex \(C = 10^{-2}\) mole/liter \([\mathrm{O_2N\Phi CH_3 + CH_3\Phi ONa}]\) (7, 9, Fig. 2); 2) when the concentration is increased from \(10^{-4}\) to \(10^{-2}\) mole/liter, owing to the shift of the equilibrium

\[ \mathrm{BK} + \mathrm{AK} \rightleftarrows [\mathrm{BK}\ldots \mathrm{AK}] \]

to the right, \(\varepsilon\) at 420 mµ increases (4, 4a, 9, 9a), and the absorption edge shifts toward longer wavelengths.

However, whereas for a solution of the components the formation of the complex at \(C = 10^{-4}\) mole/liter almost disappears (7, 7a, Table 1), in the case when the components AK and BK are connected with one another by the group \(Q = \mathrm{CH_2CH_2}\) and \(\mathrm{CH_2}\), the exo-interaction is manifested to a considerably greater extent; the band lies at considerably larger values of \(\varepsilon\), and lowering the concentration causes a greater decrease in the value of \(\varepsilon\) (9, 9a, Fig. 2). This indicates that, in the case when the components of the complex are connected with one another in the molecule by the group \(Q\), the conditions for formation of complex (IV) are more favorable \((\mathrm{CH_2CH_2} > \mathrm{CH_2})\) than in the case when the components are two independent molecules.

Fig. 1

In the case of weak donors \(A^2 = \mathrm{OH}, \mathrm{NHCOCH_3}\) in alcohol, even at \(C = 10^{-2}\) mole/liter, almost complete coincidence is observed with the spectrum calculated for the sum of the components (3 and 1, 8; 12 and 10, 13): \(\varepsilon_{\max}\) of band \(I^b\) for Nos. 10, 13 is a consequence of the superposition of the component bands (12, Table 1). Exo-interaction in an incipient form is manifested here only in a small shift of the absorption edge relative to the calculated curve, more clearly when the concentration is increased from \(10^{-4}\) to \(10^{-2}\) mole/liter. That the indicated effect is a consequence of exomolecular interaction is evident from the fact that the magnitude of the bathochromic shift of the absorption edge increases 1) when the concentration is increased from \(10^{-4}\) to \(10^{-2}\) mole/liter and 2) when the \(\mathrm{CH_2}\) group is replaced by \(\mathrm{CH_2CH_2}\).

A small effect of endomolecular interaction is manifested only in insignificant bathochromic shifts of bands \(I^b\) and \(II^a\) with some increase in \(\varepsilon\). This effect was explained from the standpoint of the theory of inductively interacting systems (5). The assumptions (8) concerning the presence of a single conjugated system are erroneous; the influence of \(\mathrm{NO_2}\) on the decrease in the reactivity of \(\mathrm{NH_2}\) has other causes. If conjugation existed between \(\mathrm{BKA'}\) and \(\mathrm{A'KA^2}\) (I), then, in view of the considerable increase of the \(\pi\)-system and the presence of a single vector of electron displacement upon excitation by light, we should have observed a significant shift of the principal band \(I^a\).

Thus, the ability of phenolate components to form colored donor–acceptor complexes of the type of aminocomponent complexes with nitro compounds has been established. The ability has been established for phenols of the structure $\mathrm{O_2N}\Phi — Q — \Phi\mathrm{OH}$ with $Q = (\mathrm{CH}_2)_n$ to form colored salts with the appearance of an exo band as a result of extramolecular interaction. It may be assumed that, for a large value of $n$, exo—

Fig. 2

interaction may arise not only by an intermolecular route, but also intramolecularly, through bending of the chain. By the term “exomolecular” ($^{9,10}$) we include interactions between the A K and B K systems, carried out not only intermolecularly but also intramolecularly through bending of the chain when structural possibilities are present.

Laboratory of the Chemistry of Dyes and Problems
of Color at the Moscow Pedagogical
Institute named after V. I. Lenin

Received
29 IX 1961

CITED LITERATURE

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