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Happy 85th Birthday toProfessor Alexandru T. Balaban!

During many of my professional and official trips in Europe and USA during 1990-1992, many scientists that I met(some of them Nobel Laureates) immediately after finding out that I am from Romania, their first question was Do youknow Professor Balaban ? It was the easiest answer I ever responded to in my life. Yes, I do. But, I never told them howproud I was to be his undergraduate student at Polytechnic Institute from Bucharest in 1962, while he was a junior facultyin the Organic Chemistry Chair.

Alexandru T. Balaban is the most productive chemist that Romania ever had, covering a large area of topicspublished 795 papers, 9 authored books, 79 books chapters, 8 edited books, and 27 patents.

His outstanding intellectual skill was supported by a strong and permanently updated knowledge of chemical literature,and moreover he covered large and diverse areas of Chemistry. It is not my aim here to dive into too many technicaldetails; those are nowadays easily available on public domains. I will rather emphasize, hopefully, in part the essence ofProfessor Balaban scientific achievement combined with a more sentimentalist approach on his superb chemistry andhuman traits. Some of my comments will be illustrated with excerpts from publications that bring some recollectionsfrom those passing years.

During 60+ years of active involvement in chemistry research, Professor Balaban showed preference for bothexperimental and theoretical chemistry fields. However, the balance was modulated by objective justification (mostlyregarding financial resources for chemicals, journals, books, instrumentation, etc.).

A. Experimental chemistry1. Reactions catalyzed by aluminum chloride.2. Heterocyclic compounds: Pyrylium salts, oxazoles, boron compounds.3. Free Radicals.

B. Mathematical Chemistry:1. Graph theory

A1. Friedel-Crafts chemistry was the favorite topic for Professor Nenitzescu. Professor Balaban was admitted asgraduate student (Professor Nenitzescu being his PhD mentor) in 1953, before finishing the undergraduate studies,and successfully defended his Thesis in 1959. The Thesis provided chemistry for 15 papers mostly published in peerreview journals and two chapters in a Monograph. Two notable achievements have emerged from his Thesis.

Contribution to understand the Scholl reaction (discovered in 1910), and lately used to synthesis of graphene nanoribbons.

A Scholl intramolecular dehydrogenation is when 1-benzoylnaphthalene is converted by AlCl3 into benzanthrone.

The expertise of Nenitzescu – Balaban team concerning AlCl3 reactions in Organic Chemistry, was quickly recognizedinternationally. Professor George Olah (Nobel Prize in chemistry in 1994) has invited Professors Nenitzescu and Balabanto write two chapters (Dehydrogenating Condensations of Aromatics (Scholl and Related Reactions) and AliphaticAcylation), in the famous multivolume Friedel-Crafts and Related Reactions (1964).

A2. The discovery of an efficient synthesis of pyrylium salts, presently known as Balaban-Nenitzescu-Praill reaction.

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This is the most cited experimental chemistry paper of Professor Balaban (Web of Science accessed January 10,2016): 125 hits.

A fascinating story, in the backstage of the PhD Thesis of Professor Balaban, that lead to the discovery of new synthesisof pyrylium salt is narrated in what follows. No references existed in the 70 years literature sources concerning therelative high distribution coefficient of pyrylium salt in water. The outstanding talent of the young chemist Balabandiscovered this fact. While I started working in Professor Nenitescu’s Organic Chemistry lab, I was fascinated to learnthat Prof. Balaban had the idea to analyze the aqueous layer where pyrylium salts are soluble. Most of the biased organicchemist arrogantly neglected this. Traditionally, during an experimental work-up the attention is focused only upon theorganic layer. This was a lesson I took home; for the rest of my professional life, I paid equally attention to the aqueouslayer of the experimental work-up.

Professor Balaban’s discovery that alkenes can be diacylated to produce pyrylium salts continued after his PhD workto enlarge the scope of this chemistry. Many papers (see Rev. Roum. Chim. 2012, 57, 535-557) and review papers on thistopics emerged from his pencil such as the first book on pyrylium salts:

A. T. Balaban, A. Dinculescu, G. N. Dorofeenko, G. W. Fischer, A. V. Koblik, V. V. Mezheritskii and W. Schroth, PyryliumSalts. Syntheses, Reactions and Physical Properties, Adv. Heterocyclic Chem., Suppl. Vol. 2, A. R. Katritzky (Ed.), AcademicPress, New York, 1982

followed by

- W. Schroth and A. T. Balaban, in “Methoden der Organischen Chemie (Houben-Weyl)”, vol. E7b, Hetarene II (Teil 2),R. P. Kreher (Ed.), G. Thieme

Verlag, Stuttgart, 1992;- T. S. Balaban and A. T. Balaban, “Pyrylium Salts” in “Science of Synthesis; Houben Weyl Methods of Molecular

Transformations”, Stuttgart, 2003;- A. T. Balaban and T. S. Balaban, in Science of Synthesis, Knowledge Updates 2013/3: Pyrylium Salts (Update 2013)

m Thieme Verlag, 2013, Stutttgart, pp. 145-216 (see an excerpt below).

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The interest for pyrylium chemistry, a domain in which Professor Balaban is so active and productive, has beenextended in the recent years from research into the syllabus of the undergraduate experimental education. MITChemistry Department is one of the few places in the world where all chemistry majors undergraduate students aresynthesizing a pyrylium salt, which in the next step is converted to N-t-butyl xylidine. In the last step of the syntheticsequence, the xylidine is incorporated into a molybdenum(III) complex. The three-coordinated molybdenum(III) complexis ultimately used to cleave the nitrogen molecule (see http://ocw.mit.edu/courses/chemistry/5-33-advanced-chemical-experimentation-and-instrumentation-fall-2007/lecture-notes/n2lect.pdf)

B. Mathematical Chemistry: chemical applications of graph theoryDuring late 50’ and early 60’ Professor Balaban started to be interested in exploring if other atoms than can conserve

aromaticity. In a systematic approach for all possible combinations of atoms capable to form monocyclic aromaticcompounds, Professor Balaban concluded that boron-containing aromatic rings are worthy of a closer examination.Later, Professor Balaban became aware that his analysis was in fact the famous graph-theoretical called thenecklace problem. Now a foot was set into starting a new domain: the graph theory. Frank Harary (the world’s experton graph theory) was instrumental in collaborating with Professor Balaban. Additionally, as a happy coincidence, theinterest in Nenitzescu’s group for [10-annulene] valence isomer and the invention by Prof. Balaban of reactiongraphs for the reaction mechanism postulated by Professor Nenitzescu for a oxidation of hydrocarbons with Cr6+ providedthe launching pad for a mature mathematical chemistry that exploded in the ensuing years. Now, we do not talk aboutBalaban reaction(s) but about Balaban index J, Balaban graphs (10-cage, 11-cage). In fact the most cited among hispapers: 810 hits (Web of Science accessed on Jan. 9, 2016) is about Balaban index J:

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Balaban cage-10 is illustrated below:Many papers have resulted from an impressive international collaboration of Professor Balaban with chemists from

USA (R. Hoffmann, NP 1985, D. J. Klein, P. v. R. Schleyer, C. Djerassi, J. A. Pople, F. Harary, A. R. Katritzky, W. Seitz), UK (A.R. Katritzky, P. F. G. Praill), Germany (W. Schroth, G. Fischer, V. Wray), France (C. Roussel, J. Metzger, C. Rulliere), Russia(V. I. Minkin, G. N. Dorofeenko) Croatia (M. Randiæ), Bulgaria (D. G. Bonchev, O. Mekenyan).

Writing these lines, I cannot ignore the harsh conditions that any chemist in Romania, prior to 1989, was exposed to ineach stage of a research producing science. Mostly during 80’ there was lack of documentation (no journals, no books),no money for chemicals and major instrumentation, and extremely complicated and painful bureaucracy to publish. Onlya few very strong and dedicated chemists have been able to survive. Definitely, our role model was Professor Balaban.

Professor Balaban is a great teacher, all the time well prepared, clear in explanation and very eloquent in all comments.I still remember how hard I struggled to be in his Organic Chemistry Section. Is still vivid a personal experience after anun-announced Quiz with two topics, one about hybridization and a second water addition to the double bond. Becauseof my extensive readings of Pauling’s original papers, I had the time to finish in one hour only the topics on hybridization.I had the pleasant surprise to see a 9+ grade (on scale 0-10) on my Quiz. Throughout my teaching carrier (50+) I alsoadopted the same attitude to highly grade a quality work even though the time limitations was precluding fully finishingthe Exam.

Vice-President of the Romanian Academy, decorated with National Order for Faithful Service by the President ofRomania, proprietor of a very impressive scientific output, part of it created in an amazing broad international collaboration,awardee of the American Chemical Society (1994), tenured tracked as Professor at the age 70 at Texas A&M Universityat Galveston, Professor Balaban now is enjoying his 85th anniversary together with family (wife Nelly, children: Silviu,Irina, the grandson Alexandru; and Silvia, granddaughter) and many, many friends!

Wishing you a Happy Birthday and at least as many more years as is the atomic number of Livermorium (Lv), namedafter the town of Livermore (Lawrence Livermore National Laboratory) where we presently live in California.

Mircea D. GheorghiuSan Jose State University,CA 95192, USA