Hattori Shuzo

Matsuoka Shin-ichi

Mori Akihiko

松岡 慎一

森 昭彦

服部 秀三

Kanazawa University Repository for Academic Resources

Proton Chemical Shifts of Molecular Complexes* By Shin聞ichiMATSUOKA，** Akihiko MORI** and Shuzo HATTORI*** (Received December 28， 1961) In troduction 45 It is well known that iodine forms molecular complexes in some solvents of which molecules have π-electrons. Up to now， these molecular complexes have been studied by many techniques and recently the absorption spectra of visible [ay and near ultra-violet region have been investigated in detail and then charac-teristic absorption spectra have been found1) in these complexes. As to the origin of these absorption spectra and the nature of the chemical binding in these complexes， there have been many interpretations， but first Mulliken has succeeded2) to give a reasonable explanation to them. He has conc1ued that molecular complexes are present because of the energy of stabiliza-tion resulting from the partial transfer of electrons from one to another of two molecules which formed the molecular complexes， and the n the characteristic absorption spectra of these complexes are called the charge transfer spectra. Since then， the molecular complexes have been studied in many branches， for example， electronic spectra， X-ray diffraction， and infra-red or Raman sp巴ctra.And som巴 studiesby means of electron spin r巴sonancehave appeared recent1y， but now， nuc1ear magnetic resonance study of these complexes is not able to be found. It may be expected that the change of electronic states of the molecules which is occurred as a result of formation of weak chemical binding in these complexes， would produce an effect on the chemical shifts of protons in these complexes， and therefore measurements were carried out on the chemical shifts of protons in solutions of iodine in aromatic substances as solvents. As samples， some pure solvents and two iodine solutions in these solvents of which iodine-concentrations are different， were prepared and proton chemical shifts of pure solvents were compared with thos巴 ofiodine solutions. Experimental procedure The proton resonance spectra were observed at 40 Mc， using a JN恥ι3type high-resolution nuc1ear magnetic resonance spectrometer of ]apan Electron Optics Laboratory Co.， Ltd. * A bries report of the measurements has been published in J. PhysょSoc.Japan 17 (1962) 1073. ** Department of Physics， Facu1ty of Science， Kanazawa University. ***Facu1ty of Engineering， Nagoya University. 46 Shin幽 ichiMATSUOKA， Akihiko MORI and Shuzo HATTORI As the first series， benzeneヲ toluene，and substituted toluenes were chosen as solvents旦ndiodine was dissolved into them so as to have two concentr旦tions，one was nearly iodine幽saturatedconcentration for e乱chsol ven t and the other was i tshalf (but， for benzene， its on巴圃third)。For measurements of the first series， thεexterna1 rεference using double-tube arrangements was employed and the sample solution was sealed in the inner tube and distilled water， as a reference substance， in the outer tube. Next， as the second series， xylene dεrivatives were taken up as solvents and sample solutions were prepared as mentioned above for the first series. In this case， both the externa1 and th巴 internal references were 巴mployed. And as a reference substance， methylene chloride was chosen rather than wat目。When the巴xternalreference was employed， a correction involving the differencε between the bulk diamagnetic susceptibilities of the reference substance and the sample was applied， ifthe bulk diamagnetic susc邑ptibilityof the solvent was known。The separation of the proton signal of the sample solution referred to the reference signal was obtained by employng the side band technique and the error of the present measurements did not exceed士 0.05ppm白Results and Discussion Th巴 resultsof the measurements for thεfirst series are summarized in Table I. In the table， for ρ開，chlorotoluene and ρ.bromotoluene， fine structures werε observ巴dfor ring proton spectra as shown in Fig. 1乱ndFig. 2， respecti vely， and therefore the chemical shifts of ring protons for these samples were not so accurate. Schaefer and Schneider have shown3) that the resonance spect日 ofmeta同protons in p-chlorotolu邑neand 1トbromotoluene appeared at 0.05 剖ld 0.07 ppm high町 field than ortho四protons respectiv巴ly. These separations betw邑enmeta司and ort加盟 protonspectra are comparable order of spin-spin coupling constants between ring protons旦t40 Mc 乱ndso complex spectra would be predicted for these compounds. J¥一Fig. 1. Fine structures of r!ng protons in t-chJorotoJuene。，~ Fig.2司 Fine structures of ring protons in ρbromotoluene。Proton Chernical Shifts of Molecular Cornlうlexes 47 A correction fo1' bulk diamagnetic susceptibilities of the 1'efe1'ence substance and the sal11ple was l11ade according to the following exp1'ession， o = o伽十 (2π/3)(x~ef -Xv)， whe1'e o and OObS a1'e the corrected and the obse1'ved chel11ical shifts， and x~ef and Zψa1'e th巴 bulkdiamagnetic susceptibilities fo1' the 1'efe1'ence subst且nce and the sal11ple. Fo1' iodine国solutions，thei1' bulk diamagnetic susceptibili ties we1'e eval uated by the 1'elation Xo (so1.) =ゆ(2)・xv (I2)十 φ(solv.)・ん (solv.)，whe1'eゆ(2)andゆ(solv.)a1'e the volul11e fractions， and x v(I2) and れ (solv.)a1'e th巴 volul11esusceptibilities of iodine and the solvents， 1'espectively. Fo1' some of the solvents， diamagnetic susceptibilities， which we1'e not known， evaluatedネ withthe aid of those of the 1'elated compounds and Pascal's constants. Table 1. Proton chemical shifts of benzene-and substituted toluene-iodine solutions. (1n ppm from water as external reference， and corrected for bulk diamagnetic susceptibility.) 12-conc. Proton chemical shift， (H -Hr) fHr Solvent (mol-%) Ring proton Methyl proton * We are indebted to Dr. J. Maruha of Chemical Department of this University for suggesting the method toestimate the unknown susceptibilities. 48 Shin-Ichi MATSUOKA，Akihiko MORI and Shuzo HATTORI From Table I， differences of the chemical shifts which were dependent upon the concentrations of iodine were not able to be found within the experimεntal errors. This fact means probably that in the molecular complexes fonn巴d in iodinトsolutions wi th th巴sesolvents， th巴 relativelarge changεof electronic st旦teswhich is able to affect the chemical shifts of solvents， is not occurred. Benesi and Hildebrand have shown1l that the iodine-mesitylen巴 complexis a much tighter one than the iodine-benzene complex. Therefore， as the second seri巴s，xylenes were chosen as solvents and sample solutions were prepar巴d in which concentrations of iodine are the same as the first series. Now， methylene chlorid邑was used as the reference substance， because the position of the spectrum of wa白人 which was used in the first seri日sas the reference， 1Ssensi ti ve to the change of the temp巴ratureand impurities contained. And also， in this series， both the internal and the extern旦1references were employed and in the case of the latteム th巴 bulkdiamagnetic susceptibility corrections were applied， as in the first serics， for the samples of which susceptibility was known. Solvent o-xylen邑問-xylenep-xylene mesJ tylene pseudo-Cumene Table I. Proton chemical shifts of xylene-iodine solutions. (In ppm from methylene chloride.) Proton chemical shift， (H -Hr) /H， 2.16 十2.68-2.12 十2.73-2.14 十2.71(-2.14 -2.05) 十2.63(-2.09 -2.05) 十2.63(-2.0ヲ -2固06)1 +2.64 -2.10 十2.63-2.10 十2.64-2.06 十2.69-1.32 十1.44-0.89 十1.91 -0・50 十2.33-2.02 十2.66 十2.73-1.99 十2.69 十2.762.00 十2.68 +2.74 -1.33 十3.61-1.35 十3.61-1.36 十3.60十3.62十3.63十3.61-0.90 十3.830.94 十3.80。.97 十3.762.35 十1.29-0.89 -0.94 十1.74十2.16十3.76 十3.90十3.72 十3.86-1.00 I +3.67 十3.77* For 0-and例-xylenes，corrected for bulk diamagnetic susoeptibility， and uncorrected for others. The results of the measured chemical shifts of protons in solvents of iodine-xyl巴nesolutions are shown in Table 1I. Of this table， complex fine structures Proton Ch仰 ucalShifts of Motecular Complexes 49 were observed for ring-proton spectra of m→cylen旦sshown in Fig. 3， and so the observed chemical shifts for these spectra were not so reliable. Also， for methyl proton spectra of pseudocumene (1， 2， 4-trimethylbenzene)， doub1et lines were obtained with intensities of 1 : 2. Fig. 3. Fine structures of ring protons in 1抑 xylene.For these samples， except 小 andm-xylenes， the correction for the bull王diamagnetic susceptibilities was not applied， since the susceptibilities of these were not found. Compared the obtained chemical shifts in the case of the internal reference with those in the external reference which were corrected for the differences of bulk diamagnetic susceptibilities for m-and o-xylenes， respectively， it is found that there are discrepancies amounting about 0.8 to 1.0 "ppm between them. This indicates that the correction for bulk diamagnetic susceptibility is only a part of corrections which are required when chemical shifts of the internal reference are compared wi th those of the external. Now， these discrepancies of chemical shifts amounting about 0.8 to 1.0 ppm are seemed to be explained by the following factorsの.About 0.5 ppm of these arises from anisotropy in the susceptibi1ity of the solvent. It is well known th乱taro-matic s01v巴ntstend to produce high field shifts in th巴 solute.1n the present case， methyl b巴nzenesolvents are seemed to shift the position of methylene chloride signal to high field by about 0.5 ppm in the internal reference case. And additional anisotropy in aromatic ring arising from formation of 7ト complexes of aromatics with reference substance， methylene chloride， is responsible for the remainder， about 0.5 ppm. To detect the differenc巴sof chemical shifts caused by chemical factors， itis desirable to employ thεinternal ref巴rence，and it is mor巴 profitable to use the reference substance which has little s01vent effects on spectra園 Therefore，it was not so suitable to use methylene chloried旦sthe reference， because it has dipole moment and is affected easily the dielectric constant of the solvents. As the referenc巴 substance，relativ巴 inertand proper one is seemed to be cycloh巴xane，50 Shin-ichi MATSUOKA， Akihiko MORI and Shuzo HATTORI C6H12， or cyclopentane， C5H10・Returned to he results in Table n， except the case of mesitylene旦ssolvents， the expected differences of chemical shifts which depend upon the concentrations of iodine are not able to be found. While， in the case of mesitylene (1，3，5ぺrimethyl開benzene) as solvents， considerable differences of the chemical shifts which depend upon the concentrations of iodine，呂refound，旦sshown in Fig. 4， and are seemed probably to be significant， but in pseudocum巴neas solvents， it is rather surprising that the similar differences does not exist. Now， more precise measurements employing cyclohexane as thεinternal reference substance and some theoretical considεrations on thεresults are in progress. ? ?? ?me廿lyl-H;--一寸12 conc. (moレ%) 1 1 u 0.0 1. 1 Ii弘山3.3 主主Fig. 4. Iz-concentration-dependent proton chemical shifts of mesitylene。Magnetic field increases from left to right. Proton Chemical Shifts of Molecular Com.ρlexes 51 Aclmowledgments we wish to acknowledge our indebtedness to Dr. N. Nakagawa of the Universi-ty of Electro愉Communicationsfor the valuable discussion and to Miss R. Murotani for the preparation of several samples. References 1) H. A. Benesi and J. H. Hildebrand: J. Amer. Ch巴m.Soc. 70 (1948) 2382， 71(1949) 2703. 2) R. S. Mulliken: J. Amer. Chem. Soc. 72 (1950) 600， 74 (1952) 811. 3) T.Schaefer and W. G. Schneicler: J. Chem. Phys. 32 (1960) 1218. 4) A. D. Buckingham， T. Schaefer ancl W. G. Schneicler: J. Chem. Phys. 32 (1960) 1227. 

Proton chemical shifts of molecular complexes

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Proton chemical shifts of molecular complexes

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