SPECTRA, STABILITY CONSTANTS, AND STRUCTURES OF ANILINE-POLYNITROBENZENE COMPLEXES
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Date
1951
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Ohio State University
Abstract
The stability constants and absorption spectra of the 1:1 complexes between aniline and m-dinitrobenzene (mN) and between p-dinitrobenzene (pN) and s-trinitrobenzene (sN) have been determined by a spectrophotometric study of chloroform solutions containing the polynitrobenzenes (N) and aniline. The formation of these complexes may be represented in the equilibria, $$N + A \leftrightharpoons NA, K = (NA)/(N) [A].$$ Quantities in parentheses denote molar concentrations and [A] is the mole fraction of aniline. Our calculated values for the stability constants, K, are: $$K(mNA) = 0.72; K(pNA) = 0.70; K(sNA) = 5.1.$$ The spectra were determined in the $340-600 \mu$ range. The spectrum of the sNA complex has a maximum at $400\mu$ with $\log \epsilon = 3.4$. The extinction coefficients of the mNA and pNA complexes increase continuously with decreasing wavelength in the above wavelength range, but do exhibit pronounced inflections at ca. $380 \mu$ with log $\epsilon$ again about 3.4. Evidence for the existence of 1:2 complexes, $NA_{2}$, has been obtained. Equations have been formulated which show how variations in the K's and $\epsilon$'s with solvent composition can affect the interpretation of the spectrophotometric data. The stabilities and spectra of the NA complexes can be semiquantitatively understood in terms of the quantum-mechanical theory of acid-base (in the Lewis sense) interactions formulated by $Mulliken.^{1}$ The theory indicates the improbability of certain symmeterical geometrical structures for the NA complexes. Probable structures are suggested.
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*National Research Council Postdoctoral Fellow, 1950-1951 $^{1}$ R. S. Mulliken, J. Chem. Phys. 19, 514 (1951)
Author Institution: Physics Department, University of Chicago
Author Institution: Physics Department, University of Chicago