View Article Online / Journal Homepage / Table of Contents for this issue ABSORPTION SPECTRA OF HYDROCARBONS. 1319 Published on 01 January 1908. Downloaded by University of California - San Diego 12/04/2016 06:21:24. CXXV1.-The Study of the Absoiption Spectra of the Hydrocarbons isolated from the Products of the Action of Alunzinium Chloride on Nup12tkccle.r~e. By ANNIEHOMER, Fellow of Newnham College, and JOHNEDWARD PURVIS, M.A. FROMthe products of the action of aluminium chloride on naphthalene, besides PP-dinaphthyl previously isolated by Friedel and Crafts from the same reaction, there have been isolated three new hydrocarbons which have been described in detail by one of us (Homer, Trans., 1907, 9 1, 1103). The substances isolated were : (.i) CI4Hl6, a homologue of naphthalene, either tetramethyl- or 4s2 View Article Online 1320 HOMER AND PURVIS: THE STUDY OF THE diethyl-naphthalene, more probably the former ; (ii) CZ0Hl4, /3@-dinaphthyl; (iii) c26H22, a substance supposed to be a homologue of dinaphthanthracene, C,,H14 ; and (iv) C40H26, probably tetra- naph t h yl. @B-Dinaphthylis formed by the condensation of two naphthalene molecules. It was thought that the hydrocarbon C,,HZ6 was formed by the condensation of either two PP-dinaphthgl or four naphthalene molecules, more probably by the former, as an increase in the time allowed for the action of aluminium chloride on naphthalene, or a rise in the temperature at which the reaction was conducted, caused a decrease in the amount of the hydrocarbon aad an increase in the amount of the hydrocarbon C,,H,, produced. It was suggested that the substance C261322was a homologue of dinaphthanthracene, CZ2Hl4,and its formation from alkylnaphthalenes, which are also formed during the reaction, was given as follows : The intense fluorescence of the substance suggested the presence of an anthracenoid linking, In the method of formation thus proposed, hydrogen would be eliminated from a /3-methyl group of trimethylnaphthalene. It was thought (Zoc. cit.) that further evidence as to the constitution of the respective products ?f the reaction in question might be produced from a comparative study of their absorption spectra with that of, naphthalene; and it was also suggested that the absorption spectrum of the hydrocarbon C,,H,, should be compared with that of the supposed parent substance, dinaphthanthracene, CZ2Hl4,and of picene, the isomeride of dinaphthanthracene. It mas with these objects in view that the investigation here Published on 01 January 1908. Downloaded by University of California - San Diego 12/04/2016 06:21:24. described was undertaken. EXPERIMENTAL. The hydrocarbons C,,H,,, CZ0Hll, C40H26,C26H22, were prepared according to the methods given iu the paper by Homer (Zoc. cit.). The standard strength of our solutions was taken as N/lOOO, a normal solution being considered as a solution containing one gram- molecular weight of solute in 1000 C.C. of the solution. The adjustable cell used has been previously used and described by Purvis and Foster (Proc. Camb. Phil, Soc., 1907, 14, 381). It is a modification of the very useful instrament described by Bdy and Desch (Trans., 1904, 85,1039). The results of the study of the absorption spectra of the substances under consideration have been plotted in the accompanying curve8 so View Article Online ABSORPTION SPECTRA OF HYDROCARBONS. 1321 that the abscissae represent oscillation frequencies, and the ordinates the logarithms of relative thicknesses of the solution. From eye observations we could observe directly the bands due to the hydro- carbon C26H22,and the absence df bands in the hydrocarbons C40H20,C20H14, CI4H,,; but in order to compare the absorptioncurves with those of other substances like naphthalene we decided to plot the curves in exactly the same way, so as to obtain comparable results. I. Naphthalene and C14H1,. The absorption spectrum of naphthalene has been given in detail by Hartley (Trans., 1881, 39, 153), who has shown that there are four bands characteristic of this substance, Their mean wave-lengths are : 2855 2726 2631 2550 which correspond with oscillation frequencies of : 3451 3690 3840 3921 The curve for an N/lOOO solution of the hydrocarbon C,4H16in alcohol also shows four bands (Fig. 1). The mean oscillation frequencies of these bands are as follow : 3434 3562 3680 3776 These four bands are thus nearer the red end of the spectrum and appear to be less persistent than the corresponding bands in the naphthalene curve. The curve for the hydrocarbon Cl,H,, is there- fore in accordance with the suggestion in the previous paper that this substance is an alkyl derivative of naphthalene. It is suggested on p. 1327 that the methyl groups are probably in the 1, 4, 5, 8 positions. Published on 01 January 1908. Downloaded by University of California - San Diego 12/04/2016 06:21:24. 11. The Hydrocarbons C2oHI4 and C,,H2,. N/lO,OOOsolutions of these compounds in benzene were compared. It was found that stronger solutions did not show selective absorption. The curves for both these substances in benzene show only two weak bands (Fig. 2). The mean oscillation frequencies of these bands were : For CmHI4.................... 3184 3430 For CdOHN..................... 3060 3200 The bands exhibited by the solutions of the hydrocarbon C,oH2, are nearer the red end of the spectrum than those exhibited by solutions of the hydrocarbon C20H14; but in the former case they are so weak that they may be regarded as traces, Since benzene solutions of the hydrocarbons C,,H,, and C40H2, exhibit the same type of curve, it seems reasonable to infer that these View Article Online 1322 HOMER AND PURVIS: THE STUDY OF THE substances have a similar constitution. The hydrocarbon C,,H,, has been shown to be PP-dinaphthyl by Watson Smith (Trans., 1877, 15, 551 ; 1879, 17, 224) and Chattaway (Trans., 1895, 67, 653). The hydrocarbon CdoH,,; therefore probably has the constitution which has already been suggested, namely, that of tetranaphthyl. At the present stage it is impossible to state how the two PP-dinaphthyl molecules have been condensed to yield tetrsnaphthyl. In order to compare the absorption spectrum of /3P-dinaphthyl with that of naphthalene, it was necessary to examine it in alcoholic FIG. 1. Oscillation frequencies. 31 32 34 36 38 40 Published on 01 January 1908. Downloaded by University of California - San Diego 12/04/2016 06:21:24. Full curve - C,,HI6 in alcohol. N/1000 solution.4L Dash ,, --- BfLDinaphthyl (CmH1,) in alcohl. N/lO,OOO s01~tion. solution. An N/lO,OOO solution of PP-dinaphthyl in alcohol (Fig. 1) shows three absorption bands of which the mean oscillation frequencies are : 3204 3436 3556 It is remarkable that whilst naphthalene in alcoholic solution gives four bands, PP-dinaphthyl in the same solvent gives only three bands, although PB-dinaphthyl consists of two naphthyl groups. Now there are two possible explanations of this phenomenon, which are as follows: View Article Online ABSORPTION SPECTRA OF HYDROCARBONS. 1323 (i) The diminished absorption power is due to steric hindmnce. The molecule of PP-dinaphthyl may be so arranged in space that there is crowding within the molecule such that the vibrations of some of the carbon atoms within one naphthyl group are hindered by the too close proximity of vibrating atoms in the other naphthyl group. The effect of this hindrance will be evidenced by a decrease either in tho rate or the amplitude of the vibrations of the atoms affected. In either case the effect of the steric hindrance will be evidenced by a diminished capacity for selectively absorbing light, although the increased size of the molecule will increase the general absorption. (ii) The diminished ccbsoqAon power may be due to the twisting of one naphthyl group relatively to the other. If there is twisting in one of the naphthyl groups, the atoms in that group will no longer vibrate in the same plane as the corresponding atoms in the other group. The twisting effect is probably more marked for some of the,atoms than for the others. Consider the effect of this twisting in the two extreme cases, where : (a) The atoms are practically not affected. In this case the effect of the vibrations of these atoms on a ray of light will be the same as that of the corresponding atoms in the other naphthyl group. That is to say, the corresponding atoms of the two naphthyl groups will augment each other’s absorbing power. (b) The atoms are so much twisted that they vibrate in the same plane as the corresponding atoms in the other naphthyl group, but they are now in opposite phase. In this case the vibrating atoms nullify each other’s effect on the ray of light. That is to say, if these atoms in the naphthalene molecule selectively absorbed light, they will now allow light to pass. Moreover, between these two extremes cases there will be inter- Published on 01 January 1908. Downloaded by University of California - San Diego 12/04/2016 06:21:24. mediate stages. But the total resultant effect of the various degrees of twisting of the second naphthyl group will be such that the selective absorption power of PP-dinaphthyl is less than that of naphthalene. If the above argument holds good, .the decrease in selective absorption ought to be more marked in the case of tetranaphthyl. Owing to the insolubility of this hydrocarbon in alcohol it cannot be compared with naphthalene, but a glance at the curves in Fig. 2 shows that the two bands exhibited by this substance in benzene solution are so much weaker than the corresponding bands for P/3-dinaphthyl that they are practically eliminated. This fact is in accordance with the explanation offered above.