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Theoretical Study of Furotropones 1007 THEORETICAL STUDY OF FUROTROPONES 1007 Wegen der vielen Zerfallsmöglichkeiten der bei- Experimenteller Teil den tert.-Butyl-Gruppen besitzt das Massenspektrum von 5-Oxo-2.2.8.8-tetramethyl-nonadien-(3.6) (1 h) Die Massenspektren wurden an einem MS 9-Instru- ment (AEI, Manchester) bei 150 °C Ionenquellentem- besonders viele Fragment-Ionen. Der [M-CO] peratur und 70 eV Elektronenenergie aufgenommen. Peak (m/e 162) beträgt nur noch einen geringen Die Proben wurden durch das Direkteinlaßsystem ein- Teil des Ionenstroms. Die wichtigsten Fragmentie- geführt. rungen sind im folgenden Schema zusammengefaßt. Fragmentierungen, für die metastabile Peaks auftre- ten, sind in den Schemata durch * gekennzeichnet. Die Zusammen fas sung berechneten und beobachteten Werte stimmen auf min- In der vorstehenden Arbeit wird dargelegt, daß destens ± 0,1 Masseneinheiten überein. a,a -Bis-acetylen-ketone in noch höherem Maße als Zur Synthese der untersuchten Verbindungen sei auf 4 5 andere ungesättigte Ketone unter Elektronenbeschuß frühere Arbeiten > verwiesen. decarbonyliert werden. Dieser Abbau erfordert die Knüpfung einer neuen Bindung und führt zu Diin- Radikalionen. Als Grund für diese bevorzugte De- Für Unterstützung dieser Arbeit danken wir der carbonylierung kann die strukturbedingte günstige Deutschen Forschungsgemeinschaft, dem Fonds der Che- mischen Industrie, der Stiftung Volkswagenwerk, dem Anordnung der wandernden zur aufnehmenden Wirtschaftsministerium Baden-Württemberg und der Gruppe angesehen werden. Direktion der BASF AG, Ludwigshafen/Rhein. Theoretical Study of Furotropones N. ZAMBELLI Faculty of Pharmacy and Biochemistry, University of Zagreb, Zagreb, Croatia, Yugoslavia and N. TRINAJSTIĆ Institute "Rudjer Bošković", Zagreb, Croatia, Yugoslavia (Z. Naturforsdi. 26 b, 1007—1010 [1971]; received April 19, 1971) Furotropones are predicted to be non-aromatic bicyclic molecules with polyenoid structures. Tropones fused with a furan ring, the so-called results for molecules [benzene, tropone, furan] from furotropones, represent a set of seven bicyclic iso- which the above mentioned molecules are made up. meric heteroconjugated molecules, differing only in The SCF molecular orbital method used here3 is the position of the heteroatoms. Their formulas are based on the HÜCKEL sigma-pi approximation4; given in Fig. 1. In the past a rather limited research the contribution of the sigma bonds to the heat of on these molecules was carried out in both ways: atomization being written as a sum of the bond experimentally1 and theoretically 2. energies, while that of the pi bonds is calculated Here we wish to report some SCF MO results for by DEWAR'S variant of POPLE'S SCF MO method 5. the ground states of the isomeric furotropones. We The essential difference between these two methods also wish to make comparison between them and is in choosing the key parameter of the theory: one- isomeric benzotropones. Similarly, we report some electron core resonance integral ßy . In P o p I e's Reprint requests to Dr. N. TRINAJSTIC, Institut "Rudjer 3 a A. L. H. CHUNG and M. J. S. DEWAR, J. chem. Physics Boskovid", Zagreb, Croatia, Jugoslawien. 42, 756 [1965]; b M. J. S. DEWAR and G. J. GLEICHER, 1 i. e., W. TREIBS and W. HEYER, Chem. Ber. 87, 1197 J. Amer. chem. Soc. 87, 685, 692 [1965]; c M. J. S. [1954]; W. HEYER and W. TREIBS, Ann. Chem. 295, 203 DEWAR and C. DE LLANO, J. Amer. diem. Soc. 91, 789 [1955]; K. TAKASE, Bull. diem. Soc. Japan 38, 301 [1969]; d M. J. S. DEWAR and T. MORITA, J. Amer. chem. [1965]; M. J. COOK and E. J. FORBES, Tetrahedron [Lon- Soc. 91,796 [1969]. don] 24,4501 [1968]. 4 M. J. S. DEWAR, The Molecular Orbital Theory of Organic i i. e., L. KLASNIC, Z. MAJERSKI, and N. TRINAJSTIC, Z. phy- Chemistry, McGraw-Hill, New York 1969. sik. Chem. [Leipzig] 239, 262 [1968]; D. R. BURNHAM and 5 J. A. POPLE, Trans. Faraday Soc. 49,1379 [1953]. M. J. COOK, Tetrahedron Letters [London] 1968, 3771. Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung This work has been digitalized and published in 2013 by Verlag Zeitschrift in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der für Naturforschung in cooperation with the Max Planck Society for the Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Advancement of Science under a Creative Commons Attribution Creative Commons Namensnennung 4.0 Lizenz. 4.0 International License. 1008 N. ZAMBELLI AND N. TRINAJSTIC atomization] for a number of conjugated hydro- carbons 3c and heteroconjugated molecules 3d. Previous work by DEWAR and co-workers 3' 7 also indicated that the heats of atomization of classical polyenes can be written as sums of "polyene" bond energies. "Polyene" bond energies used in this work [a] Atom or ion Valence state Wi [ii,ii] [eV] [eV] C trtrtr 77 - 11.16 11.13 0 tr2tr2tr 77 [>C=0] - 17.70 15.23 5 4 0 + tr2trtr 77 6<ir)3 [>0] - 33.90 18.60 7V2 17 [b] The two-center integrals were found using the expression of 12 OHNO (K. OHNO, Theoret. Chim. Acta [Berlin] 2, 219 [1964]) [ii,jj]=e*[r*ij+lRi+Rjl*]-il* where 2 Ri=e2/[ii, ii] and 2 Rj = e2/[jj, jj]. 1 Table 1. [a] One-center integrals, [b] Two-center integrals. 13 Type of Atom Core Wt [ii,ii] Fig. 1. Topology of the studied molecules. bond charge [eV] [eV] original procedure ßfj was fitted to spectral data, C=0 C 1.100 - 12.29 11.69 while in D e w a r's variant ßfj is fitted to thermo- O 0.900 - 16.02 14.49 chemical data [thermocycle procedure 6]. Th simple C-Ö C 1.093 - 12.21 11.64 0 1.814 - 30.60 17.67 idea behind D e w a r's procedure is that parameter ßfj — good for predicting the energies of excited Table 2. One-center integrals after sigma polarization cor- states — may not be neccessarily good for the rections. ground states, as it is the case. Bond lengths cor- Bond Bond energy responding two-center integrals are recalculated at [eV] each iteration [variable beta-procedure 3b]; the final result is therefore self-consistent for variation of C-H 4.4375 integrals with bond length. The parameter values C-C 4.3499 C=C 5.5378 are given in Tables 1 — 3. C = 0 7.1575 C—Ö 4.1594 This procedure has been shown to give excellent estimates of the ground state properties [heat of Table 4. "Polyene" bond energies. Bond D" D' R" R' a" a' F G [eV] [eV] [A] [Ä] [A-1] [A-i] [Ä] [A] CC 5.5600 3.9409 1.338 1.512 2.3177 2.0022 1.512 0.174 CO 7.1011 3.9987 1.230 1.395 2.1787 1.7870 1.395 0.165 Table 3. Thermocycle data. 6 M. J. S. DEWAR and H. N. SCHMEISING, Tetrahedron [Lon- STIC, J. chem. Soc. [London], Ser. A 1969. 1754; c M. J. S. don] 5, 166 [1959] ; ibid. 11, 96 [I960]. DEWAR, A. J. HARGET, and N. TRINAJSTIC, J. Amer. diem. 7 a M. J. S. DEWAR and N. TRINAJSTIC, Tetrahedron Letters Soc. 91, 6321 [1969] ; d M. J. S. DEWAR and N. TRINAJ- 1969, 2129; b M. J. S. DEWAR and N. TRINAJSTIC, J. chem. STIC, J. Amer. chem. Soc. 92. 1453 [1970]. [London] 1969, 2129; b M. J. S. DEWAR and N. TRINAJ- THEORETICAL STUDY OF FUROTROPONES 1009 are given in Table 4. Accepting the conclusion that Molecule Bond Bond length the bonds in classical polyenes are localized 3b' 8, we Experimental Calculated are then led to a simple definition of the aromatic Benzene 1-2 1.387a 1.396 stabilization, as a difference between the heat of Furan 1—2[1 -5] 1.367h 1.371 atomization of a given conjugated molecule and 2—3[4 -5] 1.350 1.354 that calculated for a corresponding classical struc- 3-4 1.458 1.460 ture. The heats of atomization of classical structures Tropone 1—2[1 -7] 1.449° 1.45d 1.463 2—3[6--7] 1.369 1.36 1.355 of hydrocarbons and heteroconjugated molecules can 3—4[5--6] 1.431 1.46 1.452 be estimated by summing up the "polyene" bond 4-5 1.373 1.34 1.357 energies. 1-8 1,270 1.23 1.259 Table 6. Calculated and observed bond lengths [in A], Results and Discussions a A. LANGSETH and B. P. STOICHEFF, Canad. J. Phys. 34, 350 [1956]. b B. BÄK, L. HANSEN, and J. RASTRUP-ANDERSEN, Calculated heats of atomization and indices of Discuss. Faraday Soc. 19, 30 [1955]. c, d Experimental stu- aromatic stabilization for studied molecules are dies by KURODA C and by OGASAWARA and KIMURA d re- listed in Table 5. Results are interesting. Benzene, ported at the International Symposium on Non-Benzenoid Aro- matic Compounds, held at Sendai, Japan, in August 1970. tropone, and furan have distinctly different indices of aromatic stabilization. Benzene has this index Table 6], and confirms that in these ring systems rather large [20.0 kcal/mole] and can be regarded single and double bonds alternate. Bonds in benzene as true aromatic compound. On the other hand, are, of course, all of the same length. tropone and furan have small indices of aromatic The bond lengths in furan are very similar to stabilization [0.8 and 1.6 kcal/mole, respectively]. those of ci's-l,3-butadiene 12. Similarly, there is some This reflects their chemical behaviour; thus tropone spectroscopical evidence about polyenoid character and furan readily undergoes DIELS-ALDER reac- of tropone 13. tions 9'10. Therefore, we can consider tropone and Annelation of the two non-aromatic rings can furan as non-aromatic cyclic polyenoid molecules.
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