CHEMISTRY

V. A. IZMAIL’SKII and K. A. NURIDZHANYAN

ABSORPTION SPECTRA OF 4-\(\mathrm{NO_2}\)-DIPHENYLAMINE DERIVATIVES

ON THE EFFECT OF ELECTRON-DONOR GROUPS IN THE \(m\)-POSITION

AND ALKYLATION OF THE NH GROUP

(Presented by Academician B. A. Kazanskii, March 4, 1960)

The study of the spectra of 4-\(\mathrm{NO_2}\) derivatives of diphenylamine (DPA) of structure (1) \((^1)\), on the basis of the principle of decomposing the structure into separate chromophoric components \((^{2-4})\), led to the conclusion that “a single conjugated system (with participation of the \(p\)-electrons of NH) with a single excitation vector along the \(\pi\)-system is absent.”

There are two decoupled systems, \(BKA^1\) and \(A^1KA^2\) (I), each with its own laws of transition to the excited state. In the spectra of (I) we find the bands of these systems. The vectors intersecting at the central N atom (which is an isolator of conjugation) prove, in this way, to be mutually coupled, depending to a corresponding degree on one another \((^1)\). As a result of disturbance of the coplanarity (V)*, the N atom of the \(\mathrm{NH(NR)}\) group may be conjugated either with \(a\) or with \(b\). Thus, the existence of geometrical isomers of conjugation is possible \((^7)\), which may explain the chromoisomerism in \(\mathrm{NO_2}\)-derivatives of DPA.

V

* \(B\) is an electrophilic chromophoric component \((\mathrm{NO_2})\), \(K\) is a conjugated system; \(A, A^1, A^2\) are electron-donor chromophoric components.
** The scheme V is constructed with allowance for standard sizes \((^5)\) under the condition of coplanarity. The H atom is indicated by the dotted circle. The planes of the benzene nuclei \(a\) and \(b\) are rotated by \(\sim 33^\circ\) \((^6)\). In the case of NMe the angle of deviation should be larger.

The principal chromophoric system is \(BKA^1\) (I), modified by the degree of polar displacements in the ground and excited states as a result of the influence of \(A^2K\). According to the rules relating the bathochromic effect to the degree of electronic displacements,* the greater the degree of electron displacement in

\[ BKA\ n\text{-}O_2N\Phi N< \]

from the state expressed by the limiting valence structural formula (I), the lower the excitation energy by light and the greater the bathochromic effect. From this point of view, the cause of the bathochromic effect in the transition from \(n\text{-}O_2N\Phi NH_2\), \(\lambda_{\max} 371\,m\mu\), to \(n\text{-}O_2N\Phi NHC_6H_5\), \(\lambda_{\max} 395\,m\mu\) (\(\Delta\lambda +24\,m\mu\) in ethanol and \(+34\,m\mu\) in cyclohexane) should be sought in the increase of electronic displacement and of the charge \(\Delta+\) on the N atom in the system

\[ O_2N\Phi N< \]

(II) as a result of the influence of the polar deformation of benzene nucleus \(b\) (II) (\(\delta-\) enhances the deformation). The influence of phenyl is thus close to the influence of alkyls, which

Table 1

Spectra of compounds in 95% ethanol*

* Nos. 1–6 and 27–30 were measured at \(C = 10^{-4}\). The remaining spectra at \(C = 10^{-3}\). \(\sim\lambda_{\max}\) was determined approximately from the bend of the curve; in parentheses are given \(\lambda\) and \(\varepsilon\) of a band whose origin is still unclear.
** \(Me=CH_3;\ Et=CH_2CH_3;\ Pr=CH_2CH_2CH_3;\ \text{iso-Pr}=CH(CH_3)_2;\ Ac=CH_3CO\).
*** The subdivisions of the bands of the \(BKA\) system into \(x\) and \(x'\) are given in the sense of \((^{9,11})\).

appears in the transition from \(n\text{-}O_2N\Phi NH_2\) to \(n\text{-}O_2N\Phi NMe_2\) (\(\lambda_{\max} 390\,m\mu\)) and \(n\text{-}O_2N\Phi NE_2\) (\(\lambda_{\max} 400\,m\mu\)). Hence one could expect that the greater the electron-donor activity of group \(A^2\) in (III), the greater the polarization of the system \(A^2K\), the greater will be \(\delta'\)-(III), and hence the greater will be \(\Delta'+\) on NH and the greater will be the bathochromic effect: \(H<NHCOCH_3<OCH_3<NH_2<NMe_2\) (\(\Delta\lambda = 0,\ +2,\ +5,\ +10,\ +15\)) \((^1)\). Thus were

* This rule was stated by Izmail’skii as a consequence of the hypothesis of the relation between color and mesomeric structure as early as 1915 \((^{7,8})\), and later by Lewis and Calvin \((^9)\).

the previous conclusions were confirmed \(^{(10)}\). These effects \(\Delta \lambda\) are considerably smaller than those values (\(+40\) to \(+120\) m\(\mu\)) which would have occurred if the conjugated chain had in fact been lengthened by \(4\pi\)-electrons. The conjugation of \(n\)-\(A^2\) with \(\mathrm{NO_2}\) is disrupted by the absence of coplanarity \(^{(5)}\). The aim of the present study is to test the influence on the spectrum of \(A^2\) in the \(m\)-position (IV) and to determine the effect on the spectra of \(n\)-\(A^2\)- and \(m\)-\(A^2\)-substituted compounds (V) of a further disruption of coplanarity by introducing an alkyl group into NH (Table 1).

According to calculations of molecular diagrams for \(\mathrm{C_6H_5NH_2}\), the electronic charges at \(m\)-C are lower than at \(n\)-C and at the C atoms of the unsubstituted benzene

Fig. 1. 1, 2, 8, 27—see Table 1; \(I\)—\(n\)-\(\mathrm{O_2N\Phi NH\Phi OCH_3}\)-\(n'\)

nucleus \(^{(12)}\). It could therefore be expected that, in the case of \(m\)-derivatives (IV), hypsochromic effects would be observed, since \(\delta'''^{-} < \delta^{-} < \delta'^{-}\). Indeed, for \(m\)-\(A^2 = \mathrm{H}, \mathrm{OCH_3}, \mathrm{NHCOCH_3}, \mathrm{N(COCH_3)_2}, \mathrm{NH_2}, \mathrm{NMe_2}\), \(\Delta \lambda = 0, -2, 0, -7, +4, +8\) m\(\mu\) (Table 1, Nos. 1–6). The presence of a negative effect thus appeared clearly for \(m\)-\(\mathrm{OCH_3}\) and \(m\)-\(\mathrm{N(COCH_3)_2}\). However, for strong donors (\(m\)-\(\mathrm{NH_2}\) and \(m\)-\(\mathrm{NMe_2}\)) the effects were positive in character (\(+4, +8\)), although according to the molecular diagrams by the molecular-orbital method a negative effect could have been expected here as well \(^{(12)}\).

If the concept set forth above—of the influence of the magnitude of the charge \(\delta'''^{-}\) on the magnitude of the charge \(\Delta''^{+}\) (IV) and on the spectrum—is correct, then it must be admitted: 1) in the case of such strong donor groups as \(\mathrm{NH_2}\), \(\mathrm{NMe_2}\), the total electron density in benzene nucleus \(b\) is increased so much that in the \(m\)-position to \(\mathrm{NH_2}\), \(\mathrm{NMe_2}\) there is a greater electronic charge than in the unsubstituted benzene nucleus \(e\)(III), i.e., in the case of \(\mathrm{NH_2}\), \(\mathrm{NMe_2}\), \(\delta'''^{-} > \delta^{-}\); 2) according to our spectroscopic data, calculations of electronic charges in the molecular diagrams of \(\mathrm{C_6H_5NH_2}\) are not sufficiently accurate (the discrepancy between values calculated by the molecular-orbital method and by the mesomeric method \(^{(12)}\) says the same). On the other hand, the spectroscopic data obtained by us, indicating definite differences in the effects of groups on the electronic charge at the \(m\)-C atom for groups of the type \(\mathrm{NHCOCH_3}\), \(\mathrm{OCH_3}\) and groups of the type \(\mathrm{NH_2}\), \(\mathrm{NMe_2}\), are in agreement with values of the electron-density estimate based on the magnetic parameter \(^{(13)}\).

Upon alkylation of NH for H, Me, Et, \(\mathrm{C_3H_7}\), iso-\(\mathrm{C_3H_7}\), \(\Delta \lambda = 0, -8, -3, -4, -5\) m\(\mu\) (Table 1, Nos. 1, 7, 12, 17, 22). Such a strong hypsochromic effect of \(\mathrm{CH_3}\) (1, 7) is explained by disruption of coplanarity of nuclei \(a\) and \(b\) and by withdrawal from conjugation of the N atom of the \(\mathrm{NR\Phi}\) group with nucleus \(a\) (as na-

was observed for $\mathrm{NMe_2}$ ($^{14}$)). The action of other alkyls was analogous in character, but it varied depending on the competing inductive and steric influences. On introducing $n'\text{-}A^2$ into $n'\text{-}\mathrm{O_2NФN(Me)Ф}$, a bathochromic effect was observed: for $n\text{-}A^2=\mathrm{H}, \mathrm{OCH_3}, \mathrm{NHCOCH_3}, \mathrm{NH_2}, \mathrm{NMe_2}$, $\Delta\lambda = 0, +1, +4, +10, +10$ m$\mu$ (Table 1, Nos. 7–11). This confirms the hypothesis that here, as in the case of (III), there is only inductive interaction of $BKA$ and $A^2K$. If $\lambda_{\max}$ for Nos. 8–11 is compared with $\lambda_{\max}$ of the parent No. 1, then the effect of $n\text{-}\mathrm{OCH_3}$ and $n\text{-}\mathrm{NHCOCH_3}$ is clearly hypsochromic, $\Delta\lambda = -4, -4$ m$\mu$, and only for $n\text{-}\mathrm{NH_2}$ and $n\text{-}\mathrm{NMe_2}$ is $\Delta\lambda =$

Fig. 2. 1, 5, 10, 29—see Table 1; II—$n\text{-}\mathrm{O_2NФNHФNH_2}\text{-}n'$

$= +2, +2$ m$\mu$. Unexpectedly, on introducing into No. 7 $m\text{-}A^2=\mathrm{OCH_3}, \mathrm{NHCOCH_3}, \mathrm{NH_2}, \mathrm{NMe_2}$ (Nos. 26–30), instead of a hypsochromic effect a bathochromic effect was observed ($\Delta\lambda = +3, +3, +7, +7$ m$\mu$), the origin of which requires explanation. However, simultaneous introduction of $m\text{-}A^2$ and $\mathrm{CH_3}$ gave, in comparison with the parent No. 1, a hypsochromic effect: for $m\text{-}\mathrm{OCH_3}$ and $m\text{-}\mathrm{NHCOCH_3}$, $\Delta\lambda = -5, -5$ m$\mu$; for $m\text{-}\mathrm{NH_2}$ and $m\text{-}\mathrm{NMe_2}$, in both cases $\Delta\lambda = 0$ and $0$ m$\mu$ (Table 1, Nos. 1, 27–30).

Compounds Nos. 2–30 have been described previously ($^{15}$).

Laboratory of Dye Chemistry and Problems of Color
at the V. P. Potemkin Moscow Pedagogical Institute

Received
20 II 1960

CITED LITERATURE

$^{1}$ V. A. Izmail’skii, K. A. Nurindzhanian, DAN, 129, No. 5, 1053 (1959).
$^{2}$ V. A. Izmail’skii, Khim. nauka i prom., 3, 232, 236 (1958).
$^{3}$ V. A. Izmail’skii, Tr. 4 Soveshch. po voprosam anilinokras. khimii, 1939, Izd. AN SSSR, 1941, p. 41.
$^{4}$ V. A. Izmail’skii, Tr. 8 Soveshch. po anilinokras. khimii, 1947, Izd. AN SSSR, 1950, p. 88.
$^{5}$ A. I. Kitaigorodskii, Organicheskaya kristallokhimiya, Moscow, 1955, p. 11.
$^{6}$ A. W. Hanson, Acta Cryst., 6, 32 (1953); J. Toussaint, Bull. Soc. chim. Belg., 54, 319 (1945).
$^{7}$ V. A. Izmail’skii, E. A. Smirnov, ZhOKh, 26, 2044 (1956).
$^{8}$ V. A. Izmail’skii, ZhRKhO, 48, pt. II, 19 (1916); 50, 168 (1918).
$^{9}$ G. N. Lewis, M. Calvin, Chem. Rev., 25, 273 (1939); Usp. khim., 10, 32 (1941).
$^{10}$ V. A. Izmail’skii, A. M. Simonov, ZhOKh, 16, 1659, 1667 (1946).
$^{11}$ W. Kumler, J. Am. Chem. Soc., 68, 1184 (1946).
$^{12}$ B. Pullman, A. Pullman, Les théories électroniques de la chimie Organique, Paris, 1952, pp. 208, 171.
$^{13}$ H. S. Gutowsky et al., J. Am. Chem. Soc., 74, 4809 (1952).
$^{14}$ A. I. Kipriyanov, Izv. AN SSSR, OKhN, 1950, No. 5, 492; ZhOKh, 23, 493, 626, 874 (1953); Usp. khim., 22, 1246 (1953).
$^{15}$ K. A. Nurindzhanian, V. A. Izmail’skii, Khim. nauka i prom., 6 (1960).