NOTES
Oct., 1958
1341
and aromatic amiize~.~-5 The infrared spectra of benzenes show only slight intensity changes for very weak bands when iodine is complexed with various benzene@-7; Mulliken has pointed out that only slight changes are expected, because the charge-transfer complexing action is distributed over several atoms.8 When the complexing action is distributed over only two atoms, as for halogens in the benzene-halogen systems, the effect is observable in the infrared spectrum.9 The spectral changes in nitroaromatic-aminoaromatic systems may be due to crystal effect^,^ and may not be an important function of the formation of the complex. It was considered desirable to re-examine a nitroaromatic-aminoaromatic system and to avbid the complications of solid state spectra by studying a liquid complex formed by two liquids: nitrobenzene and aniline. Spectral variations of both components were investigated. The existence of a nitrobenzene-aniline TABLEI complex has been demonstrated by Gibson and HEATSOF FORMATION AND RADII LoefflerlO and by Weiss.I1 Crystal AHOY, radius, Conclusions are based on a quantitative investiSpecies kcal./niole A. gation of all of the bands of both components of the NOzC10* (c) 8 . 0 f0 . 4 ... complex; the most intense bands were studied NOS- ( 9 ) -89.0 2.10 quantitatively by means of special thin cells. c104- (g) -92.0 2.60 Small frequency changes were found for each of NOz+ ( 9 ) 244.5 1.02 the components, but changes of equal or greater magnitude in the spectra of carbon disulfide The derived values of the heats of formation were solutions ofappear each component. Minor intensity consistent from one compound to the next, in a changes, both positive and negative, occur for given series, to less than one kcal. from the average; both components and were found to be smaller however, in view of the approximate nature of than the changes found for carbon disulfide soluequation B, the results should not be regarded as tions of each; spectral changes appear t o be due being more accurate than five kcal. The derived mainly to solvent effects. Lack of any marked radii show internal consistency of 1 0 . 1 A. The changes assignable to complex formation might be radius for the NOz+ ion is to be interpreted as the due to the distribution of complexing action over radius perpendicular to the axis of the linear ion.* The value of the heat of formation of the nitronium many atoms, as suggested by Mulliken for benzenesion is in agreement with the value of 263 f 23 kcal. halogen systems.8 In any case, the spectrum of the derived from the ionization potential of nitrogen nitrobenzene-aniline molecular complex does not show the appreciable changes given by similar dioxide. complexes involving solid state spectra.294P6 ( 6 ) A. J. C. Wilson, editor, “Structure Reports for 1950,” Utrecht, Details of the investigation follow: Spectra of N.V.A., Oosthoek’s Uitgevers Mij., 1950,p. 435. the three liquids, nitrobenzene, aniline and 1:1 (7) Ref. 6, p. 230. nitrobenzene-aniline, and of various carbon disul(8) These values of the radii should not be taken too literally as they may easily be in error by as much as 0.2 A. They should be fide solutions of these were determined from 400 to regarded as formal values that satisfy the thermal data when inter6000 em. -I. Very thin, demountable, recessed preted b y equation B. The derived value for the nitronium ion radius cells,12 0.00025 and 0.00068 em., were used to inis a t least 0.2 A. less than would be expected on the basis of comparison vestigate the strongest bands. The weak bands with other radii. (9) E. C. G. Stueckelberg and H. D. Smyth, Phys. Rev., 86, 478 were examined by means of conventional cells. (1930). The absence of strong hydrogen-bonding in the aniline-nitrobenzene complex has been reported be known. The followine: comDounds were used to form these series: BaTC104);, NaC104, KC104, RbCIOa and B a ( N 0 A NaN03, KNOI, RbN03, CsN03. The necessary heats of formation were taken from reference 1, and the radii of the cations were taken from reference 6 . An iterative procedure was used to find values of r- for each pair of salts of common anion. The results were averaged to obtain r-. This average value of r- was used to compute AHOfx- from data on each compound. These values were then averaged. The results are presented in Table I. The ionic radius of the nitronium ion was obtained by subtracting the derived nitrate radius from the observed interionic distance (3.12 in nitrogen p e n t ~ x i d e . ~Equations A and B were then used to compute the two values for the heat of formation of the nitronium ion. The results were averaged and the average is listed in Table I.
w.)
INFRARED SPECTRUM OF T H E NITROBENZENE-ANILINE MOLECULAR COMPLEX BY R. A. FRIEDEL’ Contribution from Central Experiment Station, Bureau of Mines, U. S. Department of the Interior, Bruceton. P a . Received June 16, 1968
Appreciable changes in infrared spectral band positions and intensities have been reported for molecular complexes formed from nitroaromatics (1) Supervisory physical chemist, Bureau of Mines, Region V. U. 6. Department of the Interior, Pittsburgh, Pa.
(2) W. R. Burton and R. E. Richards, J . Chem. Soc., 1316 (1950). (3) A. N. Terenin and N. Yaroslavskii, Acto physico-chin. U.R.S.S., 1’7,240 (1942). C. A . , 87,6553 (1943). (4) H . Kainer and W. Otting, Chem. Ber., 88, 1921 (1955). (5) R. D.Kross and V. A. Frtssd, J. A m . Chem. Sac., 79, 38 (1957). ( 6 ) (a) D. L. Glusker, H. W. Thompson and R. S. Mulliken, J . Chem. Phys., 21, 1407 (1953); (b) W. Haller, G . Jura and G. C. Pimentel, ibad., 22, 720 (1954). (7) E . E. Ferguson, zMd., 26, 577 (1956). (8) R. S. Mulliken, ibid., 23, 397 (1955). (9) J. Collin and L. D’Or, mbad., 23, 397 (1955); D’Or, Alewaeters, and Collin, Rev. trau. chim., 76, 862 (1956); Person, Erickson and Buckles, J . Chem. Phys.. 2’7, 1211 (1957). (10) Gibson and Loeffler, J . A m . Chem. Soc., 62, 1324 (1940). (11) J. Weiss. ibid.. 245 (1942). (12) R. A. Friedel and M. G . Pelipetz, J . O p t . Sac. Am., 48, 1051 (1953).
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COMMUNICATION TO THE EDITOR
by Coggeshall13 and is confirmed by the present work. Other workers have reported differences between the spectra of nitrobenzene and aniline and the spectrum of the complex at 8300 to 12000 cm.-’, the region of the overtones of the NH and CH stretching bands.3 Our investigation of the 1:1 complex also disclosed differences between the spectra of aniline and of the complex in the NH stretching region from 3200 to 3450 cm.-l but the observed shift of the two free NHz stretching bands, 15 cm.-l to higher frequencies, in the spectrum of the complex are attributable merely to the solvent action of nitrobenzene. The same shifts of the free NHz bands were observed for solutions of aniline in carbon disulfide. Intensities of the NH bands are decreased by nitrobenzene, indicating that nitrobenzene produces some dissociation of intermolecular hydrogen bonds of aniline; weak hydrogen bonding between nitrobenzene and aniline is not apparent, but cannot be ruled out. Carbon disulfide produces a greater diminution of aniline N H band iiitensities than does nitrobenzene. Intensities of other aniline bands in the spectrum of the complex showed the following: (a) except for the NH bands, all bands show intensity enhancement of from 0 to 25%; (b) the largest increased intensities are %yo for the 1500 cm.-l band and 20% for the 692 cm.-l band. Except for the ’ (13) N. D. Coggeshall, footnote 10 in article by Landauer and McConnell, J . Am. Chem. Soc., 74, 1221 (1952).
Vol. 62
NH bands, the same or slightly greater enhancement of intensities was shown by the spectrum of aniline in carbon disulfide. A small shift in band position was found for the 880 cm.-l band of aniline, which shifts to 879 cm.-l in the iiitrobeiizene complex. In carbon disulfide this band shifts to 878 cm.-l. Another very small shift, 2 cm.-l to higher frequency, occurs for the unsymmetrical band of nitrobeiixeiie a t 703 cm. - l in the presence of aniline. Also, the band becomes symmetrical. The same changes occur for nitrobenzene in carbon disulfide. Small intensity changes found for nitrobenzene in the complex are: (a) most of the absorption bands showed changes; some were enhanced and some were diminished; (b) the largest enhancements were found for the symmetrical and unsymmetrical NOz stretching modes, 1347 and 1527 cm.-l, with increases of 15 and 25%) respectively; (c) the intensity of the 703 cm.-l band increased by 10%; (d) the largest diminution of intensity, 20%, was found for the 793 cm. -1 band. Substitution of carbon disulfide for aniline produces coiisiderably more enhancement of intensities; no bands of nitrobenzene in carbon disulfide showed diminution of intensities. Differences between the effects of aniline and carbon disulfide on nitrobenzene appear to be attributable to differing solvent effects. Spectral measurements by Leonard Shufler and John Queiser and purification of compounds hy Stanley Laiiger are gratefully acknowledged.
COMMUNICATION TO THE EDITOR T H E OPTICAL ACTIVITY O F COPPER HELICES
Sir: A recent publication by Tinoco and Freeman1 coiicerning the optical activity of oriented copper helices contains a misinterpretation of an important paragraph which appears in an earlier paper by Winkler.2 Both papers dealt with an extension of E(. F. Liiidman’s early work on the apparent optical activity of dissymetric systems of conductors. Tinoco and Freeman stated that “Winkler attempted to repeat this [Lindinan’s] work and claimed that the optical rotation observed (1) L. Tinoco and M. P. Freeman, J . Phgs. Chem., 61, 1196 (1057). (2) M. H. Winkler, ibid.,60, 1656 (1956).
by Lindman was due to anisotropic scattering and not to optical activity.” An exchange of correspondence with the latter authors has established that that claim was not intended. The sentence in the paper by Winkler which states that “the observed effects were due to diffraction” refers oiily to changes in intensity. No reference to optical activity was intended then. The logical consistency of the paper was somewhat dependent on the assumption) under which the paper was written, that the helices used were optically active. PROTEIN FOUNDATION, INC. MARVINH. WINKLER 281 SOUTHSTREET PLAIN 30, MASS. JAMAICA RECEIVED JULY 28, 1958
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