ric rronsmreu oy n.-v. vuae
Marietta
College, Marietta,
Ohio
45750
ugh Erich Huckel is a ph [as contributed to the somng or cnemlcal IS. We asked him about his education persuch interdisciplinary \\-orlcs.
t a o different types of electrons. This concept proved especially useful to Hiickel for it made it possible for him to interpret t,he bonding conditions in benzene, the structure of which until then had remained relatively obscure. But it, is the predictive potential of any theory that makes it especially valuable. In t,his respect, too, the two methods by Hiickel proved successful. Their prediction that all monocyclic hydrocarbonswith 4n 2a electrons ( n = 0,1,2. . .) should have "aromatic" character was subsequently demonst,rated most beautifully. The theory also explained the amazing acidity of cyclopentadiene. When this compound dissociates, a cyclopent,adienyl anion is formed which, with its six r electrons in a planar fivc-membered ring, obeys the Hiickel rule. I n 1954 W. v. E. Doering could demonstrate that the wellknown salt-like compound obtained by bromination followed by heating of cycloheptatriene was the tropylium bromide. The tropylium cation with it,s six a electrons in a planar seven-membered ring is lilcexise a Huckel system. Finally R. Breslow was successful in the synthesis of cyclopropylium salts, which, with their two s electrons in a planar threemembered ring, represent the simplest "aromatic" compounds.
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This interview, one of a seriet which nllow* eontemporar.y chemists lo give us "firsthand" informatiun of i.he ext,emal circumst,anees and motivatdon of theil. work, was first published in C h m ~ i cin unserer Zrd, 4, 180 (1970). I'wmiision to publish a translated vel.sion was granted by Professor I h . E. Iliiekel and Verlag Chemie and in hereby gratefully acknowledged.
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Journal o f Chemicol Education
I was given excellent prerequisites o f home. M y fother hod been Internist (Specialist for internal medicine), Dozent at Tubingen and for fomily reasons had retired eorly in GGttingen. I hod two brothers. The older brother Walter I om certain you know. [Wolter Huckel, born 1895 Charlottenburg; Ph.D. GGttingen; Freiburg, Greifswald, TGbingen.1 I om the second son. M y younger brother become o pathologist and died eorly. My fother was very much interested in notural science, e.g., carried out chemical experiments with us. Early we studied Ostwald's book "Die Schule der Chemie." W e hod set up a chemical and physics loborotory. M y fother built his own opporotur with which he repeated, e.g., the experiment o f Hertz. Our fother introduced us quite eorly t o 011 areas o f noturol science. My brother Wolter had olreody decided t o study chemistry of of age 13. 1 chose t o study physics just prior to graduation from high school. I hod merely one undisturbed semester before the war commenced; in 197 5 or 197 6 1 hod t o terminate my studies completely. Since I was unfit for milifory service, I become o scientific helper of the model experiment01 station for oerodynomics. After the war I returned to the study o f physics of Gottingen and in 1920 started my docforol work under Debye-on experimental study dealing with "Scattering of X-rays by Liquid Crystolr" which 0. Lehmonn thought t o have discovered. Nothing come of it, except that these "liquid crystals" were not crystals but o f best o swarm o f ordered molecules. Beginning o f 1921 I groduoted offer Debye hod olreody moved from GGttingen t o the FTH of ZGich. When did your work with the strong electrolytes Editor: originate? HGckel: Already in 1927 Debye had wonted me t o follow him as on assisfont t o Zurich, but it was not possible since there were employment restrictions for foreigners in Switzerland. I was then offered o position os ossistont by the famous mothemotician Hilbert. A year later M a x Born gave me-likewise in GGttinoen-a oosition as on assisfont. The new quontum theory hod at thot time not yet been discovered and so Born and I worked occording t o the old quantum theory an rototionol spectra of multiotomic molecules. Everything [thot I had t o d o ] was actually spelled out. Since Born hod developed the concept, my work turned
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itor: ckel:
rrnd o f Chemical Educofian
remember. Maybe I did so on my own, or possibly my brother may hove pointed it out. I t was certainly obvious t o turn t o this problem. For a chemist, yes. For thot reason I presume that my brother hod given me a tip. Everyone worned me thot the problem wos too difficult. I was o f the opinion, however, fhot somehow it should be solvoble. The fundomental thought was thot here apparently the molecule must be viewed or a whole and not merely in terms o f the effects of neighboring otoms. That this must be so could be seen from the "directing" effects o f substituents. which transmit. somehow. the perturbotion throughout the ring. Most remor!&ble is the foct. thot when I treated the electrons in the entire m o l e c u l ~ w h e r e b y I seporoted K ond c electrons-the perturbotion goes through the whole molecule, even though I used for my calculation only the effecfs of neighboring otoms. To o certain extent this is analogous to a vibrating string, which I must view as o whole, even though the motion takes ploce through the effects o f infinitesimal-elements of the neighboring-here string, Slofer ond Bloch hod already worked out methods for calculating the effects o f electrons in o metal grit which were opplied, e.g., for the interpretation o f ferromognetism. Another procedure wosused by Bloch for electrons in metols. These hvo methods I opplied on the K electrons o f benzene. The first led finolly to the so-called VB (valence-bond); the second is presently referred t o os M O (molecular orbitol) or H M O (Huckel molecular orbital) method. The first is more volid for 11 disfonces, while the lotfer more for shor
