334s
WILLIAM L. MOSBY
1701.
75
[CONTRIBUTION FROM THECENTRAL RESEARCH LABORATORY, GENERAL ANILINE A N D FILMCORPORATIOS]
The Ultraviolet Absorption Spectra of Some Polymethylnaphthalenes B Y WILLIAM
L. MOSSY’
RECEIVED FEBRUARY 5, 1953 The ultraviolet absorption spectra of several polymethylnaphthalenes are given, and features of these spectra are discussed in connection with various properties of the compounds.
The ultraviolet absorption spectra of all of the of 2,3,5trimethylnaphthalene has been published dimethylnaphthalenes2 and twelve of the fourteen by Morton and de G o ~ v e i a ,while ~ that of the possible trim ethyl naphthalene^^ have been pre- 2,3,6-isomer seems unrecorded, although the subsented in detail. Of the two trimethylnaphthal- stance is known.5 Only one example,6 apparently, enes missing from the Swiss study, the spectrum has appeared on the ultraviolet spectra of the higher methylnaphthalenes. The syntheses and infrared spectra of some of these higher methylnaphthalenes were recently presented,’ but, unfortunately, the infrared spectrograms of these substances, like those of the dimethylnaphthalenesS are not amenable to facile interpretation. 4.0 Figure 1 shows the ultraviolet absorption spectra of four tetramethylnaphthalenes : 2,3,6,7- (A) ; u 1,4,6,7- (B); 1,4,5,7- (C); and 1,4,5,8- (D). Figure M 2 gives the corresponding curves for (D), 1,2,3,43.0 (E), 1,2,3,4,5-pentatetramethylnaphthalene methylnaphthalene (F) and 1,2,3,4,5,8-hexamethylnaphthalene (G). All of the curves show, of course, a bathochromic shift relative to the curve of naphthalene, such as is 2.0 usually characteristicg for alkyl substituted aromatic systems. However, a pronounced gradation in the degree of bathochromic displacement is 220 260 300 340 readily apparent as one progresses from comX in mp. pounds A to D. Since, in compound D, all of the Fig. 1.-The ultraviolet absorption spectra (in methanol) methyl groups occupy positions of greater conjugating power, it would be expected, in accordance of the tetramethylnaphthalenes: A , 2,3,6,7-; B, 1,4,6,7-; with PuUman’slO conclusions, l1 that this compound C , 1,4,5,7-; D, 1,4,5,8-. would show a greater bathochromic shift than other 1 I tetramethylnaphthalenes. This is clearly the case among the tetramethylnaphthalenes whose curves are shown in Figs. 1and 2, and it is almost certainly true for all other tetramethylnaphthalenes. It is apparent,l 2 even in the di-2 and trimethylnaph-
-
(4) R. A. Morton and A. J. A. de Gouveia, J . Chem. SOC.,917 (1934). (R) I*, Ruzicka and L. Ehmann, Helv. Chim. A d a , 16, 140 (1932). (6) R. Schwyzer, H. Biswas and P. Karrer, { b i d . , 34, 669 (1951). (7) W. L . Moshy, THISJ O U R N A L , 74, 2561 (1952). (8) E. E. Vago, E . M. Tanner and K. C. Bryant, J . Insl. Petroleum, 36, 293 (1949). (9) B. Pullman and A. Pullman, “Les Theories Electroniques de la Chimie Organique,” Masson & Cie, Paris, 1952, p . 515. ( I O ) B. Pullman, Compl. rend., 222, 1396 (1946); Bull. SOC. chim. France, 1 5 , 533 (1948). (11) Extensive verification of this principle is to be found in the literature, and among the examples cited in R. A. Friedel and M. Orchin, “Ultraviolet Spectra of Aromatic Compounds,” John Wiley and Sons, Inc., New York, N. Y., 1951. See also, E. Clar and Ch. 220 260 300 340 Marschalk, Bull. SOC. chim. France, 433 (1950). X in mp, (12) E. g., the following data taken from references 2, 3 and 4 : Fig. 2.-The ultraviolet absorption spectra (in methanol) di- or trimethylnaptlialene Xmax. log f of: D, 1,4,5,%tetramethylnaphthalene; E, 1,2,3,4-penta1,42 89 3.88 1,s. 2 87 3.96 methylnaphthalene; F, 1,2,3,4,5-pentamethylnaphthalene; 1,s285 3.85 G, 1,2,3,4,5,8-hexamethylnaphthalene. 2,3279 3.71 __-___2,6274 3.67 (1) Calco Chemical Division, American Cyanamid Company, 2,7275 3.69 Bound Brook, New Jersey. 1,4,5292 3.90 (2) A. S . Bailey, K. C. Bryant, R. A . Hancock, S. H. Morrell and 3 70 1,3,6284 J. C. Smith, J. Ins!. Petrolezrm, 33, 503 (1947). 3 87 2,3,6283 (3) E. Heilbronner, IJ. Frijlicher and PI. A. Plattner, Helu. Chim. 1,3,7280 3.74 Acta. 32, 2479 (1949).
July 20, 1953
ULTRAVIOLET ABSORPTION SPECTRA OF POLYMETHYLNAPHTHALENES 3349
thalenesj3 that a greater bathochromic shift is anol solutions of the compounds, using a Cary recording spectrophotometer. Thanks are due to Dr. C. E. Larrabee associated with a-than with @-methylsubstitution. for a sample of 1,2,3,4-etramethylnaphthalene which he Attention has been drawn by BadgeP to evidence prepared by a modificLtion of Hewett’s method.lg The supporting the contention that substituents in the synthesis and properties of 2,3,6,7-tetra~nethylnaphthalene~o a-position of naphthalene are conjugated with the and the other polymethylnaphthalenes’ discussed have been described. When the spectrum of 1,4,5,8-tetramethylrings to a much greater degree than are such sub- naphthalene measured in isooctane instead of methanol, stituents in the P-position. Further support for a very slight was hyperchromic displacement of the longer wave this contention may be adduced from the curves in length maxima was the only observable effect. The values Fig. 1, and the data in note 12. Both the batho- of Am,, for the different compounds together with the values of the intensity are tabularized below, chromic and hyperchromic displacements exhibited corresponding The parenthe. ized figures represent “should.rs” or inflecare significant, the greater intensity of absorption tions. evidenced, as usual, by the system having a greater degree of conjugation.14 log e Only a slight difference is detectable in the posi- 2,3,6,7-Tetramethylnaphthalene( A ) (4.04) tions of the absorption maxima exhibited by 4.06 lJ2,3,4,5-pentamethy1- (F) and 1,2,3,4,5,8-hexa3.46 methylnaphthalene (G). This is of interest in 3.58 view of the pronounced trend toward higher values 3.68 of Amax as one proceeds from the mono- to the tetra3.67 methylnaphthalenes. A further characteristic of 3.46 the absorption spectra of both F and G is the dis2.83 appearance of fine structure (especially) from the (2.67) 300-340 mp range. This latter effect might arise 2.86 from the presence of intramolecular strain. Everard and S ~ t t o n ’have ~ explained the anomalous 1,4,6,7-Tetramethylnaphthalene( B ) 4.77 dipole moments of the 4,8-dihalo-1,5-dimethoxy(3.33) naphthalenes on the basis of such distortion. This (3.59) strain should naturally be a t a maximum in the 3.76 octamethylnaphthalene, the preparation and study 3.82 of which would be of interest in this connection.l6 (3.67) This strain might also be expected to produce a 2.62 hypsochromic displacement l7 which often counter(C) 485 acts the normal bathochromic effect of methyl 1,4,5,7-TetramethylnaphthaIene (3.80) substitution. 3.87 Further, though less precise, evidence of intra(3.32) molecular strain might be inferred from the melting 2.92 points of, for example, lJ4,5,6-tetramethylnaphthal3.09 ene (D) which melts a t 132O, and the strain-free 2,3,6,7-analogj which melts a t 191’. 1,4,5,8-Tetramethylnaphthalene (D) 4.83 (3.87) 3.92 (3.83) (3.50) (3.18) 3.28
Experimental18 The ultraviolet spectrograms were obtained from meth(13) G. M. Badger, J . Chem. Soc., 2500 (1949); G. M. Badger, R. S. Pearce and R. Pettit, ibid., 1112 (1952). (14) The author is indebted t o the referee for stressing the importance of the position of substitution upon the vertical and horizontal polarizations possible within the molecule. The high intensities of the peaks a t 310 and 325 mp in (A) may find explanation on such a basis, as suggested for other @-substituted naphthalene derivatives by Y. Hirshberg and R. N. Jones [Can.J . Research, B47,437 (1949)l. (15) K. B. Everard and L. E. Sutton, J. Chem. Soc., 2312 (1949). (16) While this manuscript was in press, the synthesis of,inter alia, octamethylnaphthalene was described by B. J. Ahadir, J. W. Cook and D. T. Gibson [ibid., 8 (1953)], and the non-planar configuration as a result of intramolecular strain was confirmed through X-ray analysis by D. M. Donaldson and J. M. Robertson [ibid.,17 (1953)l. (17) See for example: A. van Dormael, Ind. chim. belgc, 15, 138 (1950); R . N. Jones, Chem. Reus., 34, 1 (1943); G. H. Beaven, D. M. Hall, M. S. Lesslie and E. E. Turner, J. Chem. Soc., 858 (1952); H. Brockmann and R. Randebrock, Chem. Ber., 84, 533 (1951); M. S. Newman and M. Wolf, THISJOURNAL, 74, 3225 (1952); M. S. Newman and H. Whitehouse, ibt’d., 71, 3664 (1949); G. M. Badger, J. E. Campbell and J. W. Cook, J. Chem. SOL, 2326 (1950); R. N. 63, 313 (1941): E. Clar and D. G. Stewart, Jones, THISJOURNAL, ibid., 74, 6235 (1952), and ref. 9 , p. 467. (18) The author is indebted to Dr. Henry Hemmendinger and Mrs. Janet Schwar for the ultraviolet measurements.
1,2,3,4-Tetramethylnaphthalene(E)
4.84
(3.70) 3.75 (2.65) 1,2,3,4,5-Pentamethylnaphthalene(F)
4.80 (3.74) 3.78 (2.87)
1,2,3,4,5,8-Hexamethylnaphthalene (G)
4.73 (3.68) 3.78
EASTON, PA. (19) C. L. Hewett, J . Chem. SOL.,293 (1940) (20) W. L. Mosby, THISJOURNAL, 76, July 20, (1953).
