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Sdreizsen , Brechung u. Absorption unges. Verbindungen. 57 gekocht. Evtl. ungelostes Pbaoporphprin a5 geht beim Zugeben des Methylats in Losung. Die Farbe geht von Rot uber eine kurze Griinfarbung nach Oliv und Braun, schlieblich in Rotbraun iiber. Nach 5 Minuten wird abgekiihlt, in 3 Liter Ather uberfiihrt und mit 0,5-proc. Salzsaure das Methylat ausgewaschen. Mit 3-proc. Salzsaure wird das Chloroporphyrin e, ausgezogen und in frischen &her uberfiihrt. Mit Diazomethan wird in iiblicher Weise verestert nnd die Atherlosung eingeengt. Das Porphyrin krystallisiert in rhombischen Blattchen vom Schmelzp. 252'. Der Mischschmelzpunkt mit Naterial anderer Darstellung ergibt keine Depression. Desgleichen ist das Spektrum mit Material anderer Darstellung identisch. Ausbeute 65 Proc. Die analoge Reaktion fiihrt vom Vinylphaoporphyrin a, zum Vinylchloroporphyrin e,. Sorensen,Bedeutung des Problems fur andere Zweige der theoretischen organischen Chemie kurz besprechen. G r u n dl a g e-n. Ein iiberaus umfangroiches spektrochemisches Material ist vor allem von J. F. Eijkman'), J. W. Briih18), F . E i s e n -lohr8) und insbesondere Ton K. von A u w e r s und seinen Schulern4) mit groDter Sorgfalt gesammelt worden. Es um-faDt fast samtliche Kbrperklassen der organischen Chemie und hat an und fir sich schon mehrmals fur die Aufklarung konstitutiver und konfigurativer Verhiiltnisse gedient. Es durfte kaum ein anderes physico-chemisches Gebiet geben, bei dem das experimentelleMateria1 derart iiberwaltigend reieh ist.AuDer der Molrefraktion bei D-Licht sind meistens die Molrefraktion fur die 3 Wasserstofflinien (ar = 6562,8, B = 4861,3 und y = 4340,5) bestimmt worden; fur die Berechnung der Dispersion im sichtbaren Licht fur ungefarbte Verbindungen reichen diese Beobachtungen vollig aus. I n neuerer Zeit werden ofters die gelbe Heliumlinie (L = 5875,7), die rote Cadmiumlinie (1 = 6438,5), sowie die 3 Quecksilberlinien 5790,7, 5460,7 und 4358,3 verwendet. Refraktionsmessungen im Ultravioletten liegen nur vereinzelt vor. Besonders V. Henri5), H. Voellmye) und T. Ed. L o w r y und C. B. Allsopp') verdanken wir ausgedehnte und sorgfatige *) Recherches refractometrique, Haarlem 1919. Hg. von A. F. 8) Vgl. das Verzeichnis der wissenschaftlichen Veriiffentlichungen 8, Spektrochemie organischer Verbindungen, Stuttgart 1912. *) Vgl. das Verzeichnis der wissenschaftlichen Veriiffentlichungen H o 11 e m an.
Sdreizsen , Brechung u. Absorption unges. Verbindungen. 57 gekocht. Evtl. ungelostes Pbaoporphprin a5 geht beim Zugeben des Methylats in Losung. Die Farbe geht von Rot uber eine kurze Griinfarbung nach Oliv und Braun, schlieblich in Rotbraun iiber. Nach 5 Minuten wird abgekiihlt, in 3 Liter Ather uberfiihrt und mit 0,5-proc. Salzsaure das Methylat ausgewaschen. Mit 3-proc. Salzsaure wird das Chloroporphyrin e, ausgezogen und in frischen &her uberfiihrt. Mit Diazomethan wird in iiblicher Weise verestert nnd die Atherlosung eingeengt. Das Porphyrin krystallisiert in rhombischen Blattchen vom Schmelzp. 252'. Der Mischschmelzpunkt mit Naterial anderer Darstellung ergibt keine Depression. Desgleichen ist das Spektrum mit Material anderer Darstellung identisch. Ausbeute 65 Proc. Die analoge Reaktion fiihrt vom Vinylphaoporphyrin a, zum Vinylchloroporphyrin e,. Sorensen,Bedeutung des Problems fur andere Zweige der theoretischen organischen Chemie kurz besprechen. G r u n dl a g e-n. Ein iiberaus umfangroiches spektrochemisches Material ist vor allem von J. F. Eijkman'), J. W. Briih18), F . E i s e n -lohr8) und insbesondere Ton K. von A u w e r s und seinen Schulern4) mit groDter Sorgfalt gesammelt worden. Es um-faDt fast samtliche Kbrperklassen der organischen Chemie und hat an und fir sich schon mehrmals fur die Aufklarung konstitutiver und konfigurativer Verhiiltnisse gedient. Es durfte kaum ein anderes physico-chemisches Gebiet geben, bei dem das experimentelleMateria1 derart iiberwaltigend reieh ist.AuDer der Molrefraktion bei D-Licht sind meistens die Molrefraktion fur die 3 Wasserstofflinien (ar = 6562,8, B = 4861,3 und y = 4340,5) bestimmt worden; fur die Berechnung der Dispersion im sichtbaren Licht fur ungefarbte Verbindungen reichen diese Beobachtungen vollig aus. I n neuerer Zeit werden ofters die gelbe Heliumlinie (L = 5875,7), die rote Cadmiumlinie (1 = 6438,5), sowie die 3 Quecksilberlinien 5790,7, 5460,7 und 4358,3 verwendet. Refraktionsmessungen im Ultravioletten liegen nur vereinzelt vor. Besonders V. Henri5), H. Voellmye) und T. Ed. L o w r y und C. B. Allsopp') verdanken wir ausgedehnte und sorgfatige *) Recherches refractometrique, Haarlem 1919. Hg. von A. F. 8) Vgl. das Verzeichnis der wissenschaftlichen Veriiffentlichungen 8, Spektrochemie organischer Verbindungen, Stuttgart 1912. *) Vgl. das Verzeichnis der wissenschaftlichen Veriiffentlichungen H o 11 e m an.
Conclusions Tung oil has a refractive index and a dispersion so far above those of any other common oil that both are valuable criteria for identification purposes. With proper equipment the dispersion, in addition to the refractive index, can be determined with little extra effort and would confirm the conclusions drawn from the refractive index. Mixtures of tung oil with another vegetable oil (except oiticica and other rare conjugated oils) can be analyzed to within 0.5% from the refractive index for either the sodium or the mercury line if the refractive indices of the separate oils are known. The mixtures can be analyzed from the dispersion to within about 1% of the correct composition if the dispersions of the separate oils are known. If the adulterating oil is not known the adulteration can be more closely estimated from the depression of the dispersion than from the depression of the refractive index. When tung oil is bodied by heat the refractive indices for the sodium and mercury lines and the dispersion fall rapidly and continuously to the point of gelation, but the changes are so similar that no worth‐while additional information is obtained by determining more than one refractive index. The fact that refractive index decreases as viscosity increases suggests the use of the refractive index in controlling the bodying of tung oil. Other things being equal, the refractive index for the mercury line should give more accurate information on tung oil than that for the sodium line because of the greater changes in the refractive index for the mercury line upon adulteration or heating. A correlation coefficient of 0.83 was found for refractive index with the diene number of tung oil. A lower correlation coefficient was found for refractive index with the iodine number, but the latter would probably be higher if a more accurate method for the determination of the iodine number of tung oil were available.
This paper is the first of a series on the application of intensity calculations to the spectra and related properties of organic compounds containing conjugated or resonating double bonds. It is concluded that in most cases the characteristic strong absorption of such compounds (giving color if the number of conjugated double bonds is large enough) is due to an N→V transition (homopolar normal state→ionic excited state) similar to those already identified in paper II for I2, O2, C2H4, and other molecules. The present paper is devoted primarily to conjugated dienes. Unconjugated dienes and polyenes are treated incidentally, and it is shown theoretically that their ultraviolet spectra should be similar to those of alkenes (C2H4 and derivatives). There should be no strong absorption peak above λ2000, and the intensity per double bond should be about the same as in alkenes. These conclusions are in agreement with the rather scanty experimental data (examples, diallyl, rubber). Detailed calculations are made on 1, 3-butadiene by the molecular orbital method, assuming all the atoms to be in one plane. The results are applicable also to other conjugated dienes. Four N→V transitions must occur for the unsaturation electrons, i.e., those electrons which make the second or weaker bond in double bonds. This group of four transitions corresponds to the one N→V transition in alkenes; according to the calculations, the total absorption intensity per double bond is considerably increased by conjugation, especially if the molecules are in the transform. Conjugation causes the frequencies of the four transitions to scatter toward both longer and shorter wave-lengths as compared with alkenes, as Hückel's work implicitly shows. Although the calculated frequencies of the four transitions are independent of the shape of the molecule (within the range of reasonable assumptions), their intensities are very different for the cis- and trans-forms, and are also very sensitive to the bond angles. There is a marked tendency for the intensity to concentrate in the longer wave-length at the expense of the shorter wave-length N→V transitions, especially for the trans-form. In the latter, nearly all the intensity is concentrated in the longest wave-length of the four N→V transitions. This gives an essential clue to the explanation of the spectra of molecules containing conjugated polyene chains, e.g., carotene and related pigments, as will be shown in VI of this series. Comparison of the theoretical predictions with available data on the ultraviolet spectra of dienes shows in general good agreement if we suppose that butadiene and its derivatives exist in the trans-form, except that perhaps its centrally-substituted derivatives (e.g., isoprene) exist partly in the cis-form. This conclusion is in line with other evidence. The available data are, however, somewhat conflicting, and systematic new measurements on the ultraviolet spectra of dienes and polyenes would be extremely valuable. The cyclic dienes, which are necessarily cis, show much weaker absorption in their longest wave-length N→V absorption region than do the open-chain dienes, just as predicted; the cyclopentadiene absorption is half as strong as that of cyclohexadiene, also as predicted in view of the different bond angles in the two rings. The absorption in both these molecules, begins, however, at abnormally long wave-lengths. This can be explained by ``hyperconjugation,'' as will be shown in IV of this series. Application of the electron-pair bond method to the problem of the spectra of polyenes is briefly discussed. Sklar has suggested that transitions to excited states which are predicted by consideration of resonance among neutral canonical structures can account for long wave-length absorption and color in organic compounds. It is here tentatively concluded, however, that such transitions are probably in general weak, and that they are not always the longest wave-length absorption transitions.
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