Biographical Memoirs: Volume 46 (1975)

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ARTHUR MICHAEL August 2, 1853-February 8,1942 BY LOUIS F. FIESER THE FOLLOWING MINUTES were placed upon the records of the Faculty of Arts and Sciences of Harvard University at the meeting of May 18, 1943.~ "Arthur Michael, Professor of Organic Chemistry, Emeritus, died on February 8, 1942, in Orlando, Florida, in the eighty- ninth year of his age. Michael was born in Buffalo, New York, on August 7, 1853, the son of John and Clara (Pinner) Michael. He attended the Briggs Classical School in Buffalo. No formal classes in chemistry were held there at that time but Michael had special instruction in this subject at school from one of his teachers, and he performed the experiments by himself with great enthusiasm in a laboratory which his father had fitted up for him at home. "Thereafter, Michael had planned to go to Harvard College, but a serious illness intervened. As a result the Michael family, in the summer of 1871, went for a long sojourn in Europe. They arrived in Berlin just in time to see the German Army, fresh from the Siege of Paris, march triumphantly down Unter den Lind en. "After he had recovered from his illness and after an in- terval of preoccupation with art and literature, Michael suc- ~ E. W. Forbes, L. F. Fieser, and A. B. Lamb, "Arthur Michael," Harvard University Gazette 38(1943):246. 331

332 BIOGRAPHICAL MEMOIRS ceeded, in spite of his meager chemical training, in gaining admission to the Chemical Laboratory of Professor Hofmann at the University of Berlin. A year later, Michael transferred to Heidelberg for two years of study under the renowned Bunsen, who ever remained his scientific paragon. He returned to Berlin in 1876 for two years of study, and it was then that he began the execution and publication of his remarkably long series of brilliant and important researches. Hofmann was the outstanding organic chemist of Germany and his laboratory at that time was the focal point of the world for research in organic chemistry, and there Michael became acquainted with many of the future leaders in that field, among them Ira Remsen and our own Charles Loring Jackson. Michael concluded his student years by spending another year at the Ecole de Me'decine in Paris under the great Wurtz. "In 1880, Michael returned to America, and after a short period as Assistant in the Chemical Laboratory at Tufts Col- lege, was appointed Professor of Chemistry at that institution. He was able to devote practically all of his time to research and with the aid of private assistants and graduate students prose- cuted his investigations with great energy and success. Among the graduate students who came to study with him at that time was Miss Helen Abbott of Philadelphia. She and Michael were married in 1889, and after an 18 months' tour around the world, Michael accepted a position as Head of the Department of Chemistry at the recently established Clark University. This position soon proved most uncongenial, and after a few months he resigned and established a residence and a private laboratory on the Isle of Wight, where he pursued his researches for four years. In 1894, he resumed his professorship at Tufts College and remained there until 1907 when he became Professor Emeritus, whereupon he established a private laboratory on his estate at Newton Center. "In 1912, Michael was appointed Professor of Organic Chemistry at Harvard. He gave no lecture courses. At first his

ARTHUR MICHAEL 333 research students and his private assistants worked with him in his laboratory at Newton Center, but during his later years, they carried on their experimental work at the Converse Lab- oratory, reporting at frequent intervals to Professor Michael at his home. Michael became Emeritus here in 1936, nineteen years after he had taken a similar status at Tufts College. "Next to chemistry, Michael's chief interest was in art, especially ancient and medieval art. He began collecting at an early date and his home in Newton was a repository of thou- sands of rare objects of art. Through his friendship with Pro- fessor Fenollosa, his attention had been directed particularly to oriental art, and objects from the Orient were numerous and conspicuous in his collections. He also had a fine collec- tion of Early American silver. As might have been expected, Michael's erudition regarding the innumerable items of his collection was encyclopedic. At his death he bequeathed his American silver to the Smithsonian Institution and the mainder of his collection to the Albright Art Gallery in his native city of Buffalo. "As a young man, Michael passed many of his vacations among the mountains; the Alps, the Canadian Rockies, and the Selkirks. Indeed, he became a real mountain climber. Thus, in 1897, he was in the party that made the first ascent of Mount Lefroy, and a few days later, with Professor Fay of Tufts College, he made the first ascent of Mt. Victoria. These are the two splendid ice-capped peaks which dominate the vista at Lake Louise. re- . "Michael was an eager, alert, but retiring personality, deeply Immersed in his scientific and artistic pursuits. He had few intimates and he shunned publicity. Indeed, he declined to accept the award of a famous medal because of the publicity which this would entail. As a teacher, he was stimulating and inspiring and uncompromising in his insistence on thorough- ness and accuracy. In his home, among his beautiful Chinese porcelains and bronzes, his Greek and Roman statuettes, his

334 BIOGRAPHICAL MEMOIRS medieval works of art, with his extraordinary cosmopolitan background of experience and acquaintance, he was an incom- parable host. "Michael was always very fond of children, although he never had any of his own. It is not surprising, therefore, that in his will, after disposing of his art collection, his library, and his chemical apparatus, he bequeathed the residue of his considerable estate to three Buffalo institutions for the care of crippled, blind and needy children. "Michael's research activities were prodigious and remark- ably prolonged. The first of his 225 separate articles describing his researches was published when he was twenty-three years old; the last appeared a few months after his death sixty-six years later. It would be idle to attempt to recapitulate these many contributions; a few may be mentioned for which he will be particularly remembered. "Michael was the first to synthesize a natural glucoside (helicin, 1879), and the method that he introduced has become the standard synthetic route to this important class of com- pounds. Another landmark was his discovery, in 1887, of the addition of active-hydrogen reagents to a!,,B-unsaturated esters and carbonyl compounds; this, the Michael reaction, proved capable of wide elaboration and, in one or another of many modifications, constitutes an important tool of the modern builder of molecules. Another general synthetic method dis- covered by Michael, a modification of the Perkin Reaction, is extensively used for the condensation of aldehydes and malonic acid (1883~. Finally may be mentioned his discovery of chlorine heptoxide, in 1900. "This enumeration might seem to imply that Michael was concerned chiefly with the experimental rather than the theo- retical aspects of chemistry. Actually the very opposite was the case. Michael was passionately interested in the theories of organic chemistry; that is, the fundamental laws and the mechanisms which might explain the marvelous variety and

ARTHUR MICHAEL 335 multiplicity of the compounds of carbon. All of his researches were undertaken to shed some light on these fundamental ques- tions, and his numerous and far-ranging experimental investi- gations did, as a matter of fact, lead to the elaboration of a general theory of organic reactions. He developed special con- ceptions of the nature of valence, the condition of unsaturated systems, and the forces involved in chemical reactions, and he formulated a principle according to which 'every chemical system tends to so arrange itself that the maximum of chemical neutralization is attained.' "While a few of Michael's collaborators learned to apply his method of reasoning, the Michaelian theories have had but little following, even though accorded the prominence of a special chapter in F. Henrich's treatise on the Theories of Organic Chemistry. Nevertheless, Michael himself, with his keen intuitive faculty, his wide experience in the laboratory, and his vast knowledge of the literature, could apply these concepts with extraordinary success both in the interpretation of known phenomena and in the prediction of unexplored happenings. Theories that can be thus applied certainly have a prima facie justification. "The vigor of Michael's interest in theory and his extreme independence of thought were responsible for another im- portant function which he performed throughout his long career to the great advantage of chemical science, namely, that of a sharp and penetrating critic of accepted views. "When the van's Hoff theory of geometrical isomerism was gaining general acceptance through the able exploitation of Wislicenus and others, Michael flatly refused to accept what to him was an unproved hypothesis. Alert to any opportunity to attack current doctrine, he saw the weakness in Wislicenus' assumption that additions to unsaturated substances necessarily proceed in the cis direction and, in- a series of carefully planned experiments, proved conclusively that bans addition does in- deed occur. He thereby corrected an erroneous feature of this

336 BIOGRAPHICAL MEMOIRS theory, but far from overthrowing the basic theory itself, his work extended and greatly strengthened a general concept that soon became a fully established tenet of the science. This ex- ample can be amplified by many others. Victor Meyer's view that the sulfone grouping is not comparable with the carbonyl and other acid-formina radicals was generally accepted until Michael (1889) succeeded in demonstrating the reactivity of the methylene groups in,8-sulfonyl esters. Michael was the first to question the C-metal formulation of the metal derivatives of nitroparaffins (1888), and, in 1908, he challenged Claisen's views with regard to the relative stabilities of enolates. In 1920 he severely criticized Tiffeneau's interpretation of the pinacol and benzilic acid rearrangements, and, in 1935, he attacked the experimental basis for analogies accepted over a period of years v , ~ as supporting the hypothetical addition—elimination mechan- ism of aromatic substitutions. His own astutely planned and faultlessly executed reinvestigations of the nitration and sul- fonation of olefins proved the previously accepted analogies to be nonexistent, and indeed the hypothesis that he contested is now discarded. "Summarizing, we can say that Michael was a powerful theorist, a keen critic and a consummate experimentalist. Or perhaps with equal appropriateness we can in conclusion quote the citation opposite his name in American Men of Science describing his field of activity, which reads, "Investigations in organic chemistry bearing on its fundamental laws and theory." In a review of the Michael reaction published 112 years after the initial discovery, E. D. Bergmann, D. Ginsburg, and R. Pappy cite 1045 references to its exploration and use. They note that in its original scope the condensation is a base-catalyzed addition of an addend or donor (A) containing an c'-hydrogen atom in the system O C—CH to a carbon-carbon double bond that forms part of a conjugated system of the general formula- ~ E. D. Bergmann, D. Ginsburg, and R. Pappo, "The Michael Reaction," Organic Reactions 10(1959):179.

ARTHUR MICHAEL 337 tion C C—C O in an acceptor (B). Typical acceptors are cY,,8-unsaturated aldehydes, ketones, and acid derivatives. All R Ri R3 Rs R6 I ~ ~ ~ ~ Base O=C—CH + C: C—C- O 1 2 1 4 A B R R1 R3 R5 R6 1 1 1 1 1 O C—C—C—C—CO 1 2 1 4 1 structures containing 0 C—CH— in which the hydrogen is active by the Zerewitinoff test will serve as donors in the Michael reaction. In addition, many compounds that do not meet this test of hydrogen activity, such as acetophenone, are effective Michael reactants. Typical acceptors are ~,,8-unsaturated alde- hydes, ketones, and acid derivatives. By extension of the orig- inal scope, the Michael reaction has come to be understood to include addends and acceptors activated by groups other than carbonyl and carboalkoxyl. The wider scope includes as donors nitrites, nitro compounds, sulfones, and certain hydrocarbons such as cyclopentadiene, indene, and fluorene that contain suf- ficiently reactive hydrogen atoms. Another hydrocarbon ac- ceptor is the conjugated tetraacetylenic compound (I), which adds diethyl sodium malonate as follows: CH3C_C—C_C—C_C—C_CCH3 + CH2(C02C2H~2 (I) Base CH3C_C—C_C—C—C—CH C(CH3)CH(CO2C2H5)~ The review article cited discusses the mechanism of the Michael reaction, the nature of the anion of the adduct, and the reverse, or retrograde Michael reaction, used for example in establishing the course of the biosynthesis of cholesterol, the question of para-bridged intermediates, the stereochemistry of the Michael condensation, and related topics. In presentin~ a

338 BIOGRAPHICAL MEMOIRS brief sketch of "an almost legendary figure, one of those giants of the days of the dawn of organic chemistry," W. T. Read ~ described Michael as "one of the most interesting figures that has ever appeared in the scientific world." In another review t Professor Albert B. Costa, historian of science of Duquesne University with research interests in nineteenth-century organic chemistry, described Michael's synthesis of natural glucosides and noted his preparation of pyrimidines by the reaction of ureas or thioureas with ethyl sodiomalonate. However, he states: "Michael's primary concern was not these experimental con- tributions but organic theory. So concerned was he with funda- mental principles that he elaborated a general interpretation of organic reactions and developed his own conceptions of the forces involved in chemical phenomena.! Energy conversions were for him the important controlling factors in all chemical changes, and he interpreted organic reactions in terms of energy in a long series of papers from 1888 on. His novel contribution to chemical theory was to introduce the thermodynamic con- ceptions of free energy and entropy into organic structural theory in order to overcome the pictorial and mechanical inter- pretation of chemical behavior. "Michael's speculations included the genesis of the chemical elements in energetic terms (1910~. The original corpuscles of matter were exclusively carriers of free chemical energy (con- vertible into less active chemical and physical energy), and all of the bound chemical energy (only partially reconvertible into free energy) appeared gradually in time from this original reservoir of free energy. Adopting the chemical evolutionary ~ W. T. Read, "American Contemporaries; Arthur Michael," Industrial and Engineering Chemistry 22(1930):1137. t A. B. Costa, "Arthur Michael (1853-1942). Meeting of Thermodynamics and Organic Chemistry," Journal of Chemical Education 48(1971):243. :t F. Henrich, Theories of Organic Chemistry, transl. T. B. Johnson and D. A. Hahn (New York: John Wiley & Sons, Inc., 1922).

ARTHUR MICHAEL 339 ideas then in vogue, he argued that the elements appeared in sequential order. In the earlier stages of the formation of the atoms of the elements the free energy of the original corpuscles was converted largely into bound energy and heat; thus, the atoms of the less active elements were formed. As the tempera- ture rose in the process of chemical evolution, such extensive conversions of free into bound energy did not occur and more reactive elements gradually emerged. With the genesis of the radioactive elements there appeared atoms with so much free energy that they were unstable. "Having the chemical elements with their varying degrees of activity based on their free energy content, Michael set out to interpret chemical reactions. His starting point was Kekule's idea that the first stage in every chemical reaction consisted in two molecules attracting each other through their chemical affinity to form a double molecule. Michael proposed that the free chemical energy in two unlike molecules was converted in part into bound energy and heat, the stability of the double molecule being determined by the extent of this conversion. He represented the reaction between sodium and chlorine in the following manner, using dotted lines to represent the free energy and solid lines the bound energy of atoms. ' ' ' Na Na 1 Na—Na + C1 C1 ~ C1 -C1 1 1 Na Na 1 1 C1 C1 Na Na 1 1 C1 C1 Na Na 1 1 1 2NaC1 (1) (2) (3)

340 BIOGRAPHICAL MEMOIRS "In phase (1) the free energy in sodium and chlorine mole- cules resulted in the formation of a double molecule of the elements. Phase (2) represented the neutralization of the free -energy as completely as possible. Finally, the bound energy between the two sodium atoms and two chlorine atoms was converted into bound energy between sodium and chlorine, the energy of the like atoms not being sufficient to hold these atoms together. "In general, every spontaneous chemical change involved the conversion of free into bound energy. Every atom repre- sented a Reunite quantity of potential chemical energy and had a tendency toward a condition of greater stability. Free energy and the affinity relationships of the atoms determined the chemical potential of a system. "To Michael, the second law of thermodynamics was the most firmly established generalization in science. The increase in entropy that took place in every spontaneous chemical change must be the soundest-basis for organic theory. For entropy, he substituted 'chemical neutralization,' meaning by this the neu- tralization of the free energy of the reacting atoms. The greater the conversion of free into bound energy that took place the more the neutralization of the chemical forces of the atoms. He then restated the second law in chemical terms: 'Every chemical system tends to arrange itself so that the maximum of chemical neutralization is attained.' "Michael applied this general theory in detail to organic chemistry. Molecular rearrangements, addition and substitution reactions, tautomerism, and stereochemical phenomena were among the aspects of organic chemistry included within his theory. In the case of molecular rearrangements he proposed four factors which determined whether rearrangements might occur: (1) the extent of free energy among the interchanging atoms or groups; (2) their affinity for each other and for the atoms in the group to which they migrate; (3) the amount of . ~ ~ .

ARTHUR MICHAEL 341 energy required to separate migrating parts from the remaining part of the molecule; and (4) the heats of formation of the sub- stances. He related these factors to the structures of the sub- stances involved and explained a variety of rearrangement re- actions, all of which entailed an increase in entropy, or in his terms, a neutralization of surplus free energy. A rearrangement might occur if a well neutralized substance was formed, pro- vided that the increase in entropy due to the intramolecular neutralization was greater than the decrease in entropy due to factor (3~. "Michael's account of the tautomerism of nitromethane and nitrosomethane is an interesting example of the application of his ideas. Nitrosomethane (CHINO) is unstable and spontane- ously forms the oxime (CH2: N OH), whereas nitromethane (CHINOS) is stable and its tautomer (CH2: NO · OH) is relatively unstable. He noted that the nitroso group has more free energy than the nitro group, the latter having the higher heat of forma- tion. In nitrosomethane the oxygen has a strong affinity for the hydrogen of the methyl group. By changing into the oxime, much of the free energy in the nitroso group is converted into bound energy and heat; hence, there has been formed a well neutralized substance. However, the nitro group has less free energy, and its oxygen is less capable of overcoming the bound energy holding the hydrogen to carbon in the methyl group. Furthermore, nitromethane is poorer in free energy than the strongly acidic tautomer; hence, a rearrangement would result in a decrease in entropy and would not be favored. "After the proof that tautomerism was the result of a mobile equilibrium between keto and enol forms, Michael investigated the conditions of stability of the forms and showed that the phenomena depended on the energy, affinity, and entropy re- lations of the tautomers and the solvent. He proposed an inter- action between solvent and solute molecules: Keto-Solvent= Enol-Solvent. If the transformation was accomplished by an

342 BIOGRAPHICAL MEMOIRS increase in entropy, tautomerization resulted with that particu- lar solvent, the degree of tautomerization depending on the relative increase in entropy. With a large difference, only one form was stable; a small difference meant that both forms were stable. "Michael concentrated much of his work on the theoretical aspects of addition to the double bond and the behavior of active methylene compounds. He claimed that addition reac- tions played a much more important role than chemists hitherto believed, and that many substitution reactions involved addi- tions as a preliminary stage. A substitution was more often than not the end result of an addition followed by an elimina- tion reaction. His interpretation of the mechanism of reactions according to an addition with the formation of an intermediate 'addition product' proved to be an important concept. "The addition process meant that a substance was unsatu- rated, and unsaturated compounds have free energy potentially convertible into bound energy. His understanding of unsatu- ration in organic compounds was a consistent aspect of his general theory. By removal of a hydrogen atom from each carbon atom in ethane, the energy used to hold these hydrogen atoms was now employed in increasing the self-saturation of the carbon atoms. Hence, ethylene is a storehouse of potential chemical energy. "Michael published many papers on the addition of unsym- metric addenda to unsymmetric unsaturated compounds. He proposed a 'positive-negative' rule as a way of determining the course of such addition reactions: the maximum neutralization is attained by the electronegative atom or group of the adden- dum combining with the more electropositive atom of the un- saturated molecule and the more electropositive atom or group to the more electronegative atom of the molecule. In propene (CH3CH:CH2), e.g., the positive methyl radical made the cen- tral carbon more positive than the end carbon atom. Hence,

ARTHUR MICHAEL 343 hydrogen iodide (H+I-) added to form mainly the secondary iodide (CH3CHICH3), although a small amount of primary iodide was also formed in agreement with Michael's distribution principle (see below). The addition of ICI and BrC1 gave dif- ferent results. ICI (I+C1-) added to form mainly the primary iodide. Michael found experimentally that the isomeric addi- tion products were present in a ratio of 3:1 of the primary to the secondary iodide. With BrC1 the two atoms were more nearly equal in electronegativity and more nearly equal amounts of the primary and secondary bromide were formed. (He obtained them in a 7:5 ratio.) These relations were con- sistent with the energetic character of the compounds. In the addition of hydrogen iodide to propene the maximum entropy increase was realized in the formation of the secondary iodide; it has a greater heat of formation than the primary compound and thus a greater neutralization within the molecule. "The positive-negative rule also clarified Michael's malonic and acetoacetic ester syntheses. These too were instances of heterogeneous addition. Both ethyl sodioacetoacetate and methyl iodide had pronounced positive-negative properties. Their reaction involved the separation of iodine from the methyl group, the attraction of sodium for iodine compared to the attraction of sodium for oxygen, and the attraction of methyl for one of the unsaturated atoms in the ester. The methyl would tend to combine with the most negative of the unsatu- rated atoms. The positive metal directed the course of reaction ONa CH3—C=CH COOC2H5 + CH3I + + ONa O CH3—C—CH HOOCH ~ CH3 C—CH COOC2H5 + NaI I CH3 CH3

344 BIOGRAPHICAL MEMOIRS "Michael found experimentally that if the metal was less positive and the addendum more negative, e.g., silver acetoace- tate and acyl iodide, then the affinity relations were changed. The affinity to methyl was diminished more than that of metal to oxygen and the tendency of the reaction was toward substi- tution, not addition. Silver acetoacetate and methyl iodide still produced a methylated compound, but in decreased yield. If an acyl iodide was substituted for methyl iodide, substitution took place instead of addition, the acidic group attaching to oxygen. The positive and negative groups of both components distributed themselves to produce the maximum neutralization of affinities. "Since all reactions do not produce one set of products, Michael introduced his 'distribution principle': 'If two un- saturated atoms A and B are present in a molecule which ex- hibits unequal affinity towards C and D of the addendum GD, and if A has greater affinity for C than has B. addition will occur if the affinity of AC-BD is greater than that of CD, and the more readily and completely the larger the difference. In this process of addition not only the affinity of A to C and of B to D comes into action, but also that of A to D and B to C, and therefore the further possibility is presented, not only of the combination of AC-BD, but of AD-BC, and the latter in increasing proportion the nearer the two combinations AC-BD is greater than AD-BC approach one another.' Thus, the more closely two atoms of a molecule resemble each other in chemi- cal affinity for a third, the more nearly equal will be the relative number of molecules of the two compounds formed. "Another important contribution, perhaps as important as his thermodynamic theory in its direct influence on organic chemists, was Michael's role as a critic. He responsibly through- out his long career was a sharp and penetrating critic of ac- cepted views. When the theory of ;,eometrical isomerism was gaining acceptance through the work of Wislicenus and others,

ARTHUR MICHAEL 345 he refused to accept what was to him the unjustified assumption that additions to unsaturated compounds always proceeded with the formation of cis products and that eliminations oc- curred more easily with cis than with bans isomers. In a series of carefully planned experiments Michael proved conclusively that bans additions did occur and that all of the then adopted configurations of geometric isomers were erroneous. He proved that fumaric acid derivatives were the direct products of the addition of halogens and hydrohalic acids to acetylenic acids and that the fumaric configurations of halo-succinic acids lost HX or halogen more readily than the isomeric compounds with the maleic acid configuration. He argued that both cis and bans additions and eliminations may occur in a given case to yield a mixture of isomers whose relative proportions depended on conditions incompatible with any mechanical conception of the process. "Far from overthrowing the basic theory, Michael felt that his correction of it greatly strengthened stereochemistry and ensured that it would become a fully established part of organic chemistry. Where chemists such as Wislicenus had erred was in thinking that the stereochemical course of reactions could be represented by purely mechanical, geometric means; adequate understanding required the use of thermodynamic factors. "Another example of his penetrating criticism was his rein- terpretation of several types of rearrangements, as illustrated by his examination of the benzilic acid rearrangement KOH C6H.5COCOC6H5 ~ (C6H5~2C(OH)COOK He studied the explanations of the rearrangement of benzil into benzilic acid put forth by Nef and by Tiffeneau and found them to be chemically impossible. Tiffeneau, e.g., proposed the addition of an alkali molecule to each carbonyl group, fol- lowed by the elimination of water and isomerization to dipo-

346 BIOGRAPHICAL MEMOIRS tassium benzilate. Michael pointed out that there was no experimental evidence that benzil could add two molecules of alkali or that benzilic acid formed a dibasic salt. His explana- tion was in terms of affinity and energy: the affinity of the car- bon atoms of the two carbonyl groups in benzil was greatly decreased by the attached oxygen atoms, and the compound was easily ruptured at that point. But in the presence of alkali the following reaction took place OK C6H5COCOC6H5 + KOH ~ C6H5 C—COC6H5 1 OH The alkali greatly increased the amount of energy needed to rupture the carbon-carbon bond, while decreasing the amount of energy needed to break the bond between the phenyl group and the newly saturated carbon atom. Thus, a change in affinity relations had occurred, and the system, instead of rupturing a carbon-carbon bond, was converted by migration of the phenyl group and a hydrogen atom into a salt of benzilic acid with a large increase in entropy OK OK OH 1 1 1 C6H5 C COC6H5~ C C C6H5 1 11 1 OH o C6H5 "Michael was a critic of all purely mechanical interpretations of organic.reactions, such as Victor Meyer's steric hindrance concept and Baeyer's strain hypothesis. He experimentally showed that steric hindrance was very limited and was appli- cable to the esterification of substituted benzoic acids only when hydrochloric acid was used as a catalyst. He demonstrated that the formation of esters of such acids without this catalyst proceeded as smoothly as with other organic acids.

ARTHUR MICHAEL 347 "Baeyer explained the ready formation and stability of five- and six-membered rings by postulating that the ease of forma- tion of a ring depended on the amount a bond must deviate from the tetrahedral angle of 109°28' in order to form the bond. Since the strain hypothesis did not consider the chemical affinity and energy relations nor the influence of side groups, it could not be for Michael a comprehensive explanation of ring forma- tion. He proved experimentally that with certain side groups cyclobutyl derivatives were as easily formed as any derivatives of five- or six-membered rings. He prepared a four-membered ring compound by the addition of ethyl sodiomalonate to ethyl citraconate COOC2H,~ ONa CHIC—C CHCOOC2H, + HC C—OC2H COOC2H5 CH3—C—CH2COOC2Ha ~ ONa 1 / C C' 1 \ I OC,2Ha COOC2H5 \ COOC2H5 COOC2H5 —C~H5OH CH3—C—CHCOOC2H5 1 1 C C—ONa COOC2H5 To Michael, the strain hypothesis required significant modi6- cation before it could over a satisfactory explanation of ring ~ . formation. "Michael's speculations were an attempt to broaden and develop structural theory in organic chemistry. Structural theory was too mechanical and the attempts to remedy its de- fects were always along mechanical lines, such as conceptions of new kinds of valencies (partial, dissociated), oxonium and carbonium theories, steric hindrance, etc. All of these were inadequate to the challenge, for they all failed to consider energy-affinity relations. For Michael, all the forces in nature

348 BIOGRAPHICAL MEMOIRS had the same end: the realization of the maximum increase in entropy, and a sound chemcial theory must have this funda- mental law as a basis. He stressed the need for thermochemical and physico-chemical investigations in order to reveal the inti- mate connection between energy relations and chemical be- havior and hoped that the union of thermodynamical principles with structural theory would lead to a more profound science of organic chemistry. His Harvard colleagues, in summarizing his contribution to chemistry, referred to him as 'a powerful theorist, a keen critic and a consummate experimentalist.' "

ARTHUR MICHAEL BIBLIOGRAPHY KEY TO ABBREYIATIONS 349 Am. Chem. .T- American Chemical Journal Ber. dtsch. chem. Ges. Berichte der deutschen chemischen Gesellschaft }. Am. Chem. Soc. Journal of the American Chemical Society |. Org. Chem. Journal of Organic Chemistry ~. prakt. Chem. {ournal fur praktische Chemie Ann. Chem. = ~ustus Liebigs Annalen der Chemie 1876 Uber die Einwirkung von Kaliumsulphhydrat auf Chloralhydrat. Ber. dtsch. chem. Ges., 9:1267. With T. H. Norton. Trijodresorcins. With S. Gabriel. Uber die Darstellung und Eigenschaften des Ber. dtsch. chem. Ges., 9:1752. 1877 Uber die Einwirkung von wasserentziehenden Mitteln auf SaureanLydride. Ber. dtsch. chem. Ges., 10:391. Zur Darstellung der Paramidobenzoesaure. Ber. dtsch. chem. Ges., 10:576. With T. H. Norton. Uber die Diamidosulphobenziddicarbonsaure. Ber. dtsch. chem. Ges., 10:580. With A. Adair. Zur Kenntniss der aromatischen Sulphone. Ber. dtsch. chem. Ges., 10:583. Uber die Einwirkung des Broms auf Aethylphtalimid. Ber. dtsch. chem. Ges., 10: 1644. 1878 With L. M. Norton. Uber die Einwirkung des Chlorj odes auf aromatische Amine. Ber. dtsch. chem. Ges., 11:107. With A. Adair. Zur Kenntniss der aromatischen Sulphone. Ber. dtsch. chem. Ges., 11:116. 1879 Uber die Synthese des Phenolglykosides und des Orthoformylphenol- glykosides oder Helicins. Comptes rendus hebdomadaires des seances de l'academie des sciences, 89: 355; also in Ber. dtsch. chem. Ges., 12:2260; Am. Chem. J., 1:305. With A. Kopp. Einwirkung verschidener Salzen auf Aldehyd Versuche angestellt. Ber. dtsch. chem. Ges., 12:2091.

350 BIOGRAPHICAL MEMOIRS On a new formation of stilbene and some of its derivatives. Am. Chem. i-, 1:312; also in [. Am. Chem. Soc., 2:42 (1880~. Laboratory Notes. I. On mono-ethylphthalate. Am. Chem. .~., 1:413; also in Ber. dtsch. chem. Ges., 13:1873 (1880~; l. Am. Chem. Soc., 2:220 (1880~. Laboratory Notes. II. On a new formation of ethyl-mustard oil. Am. Chem..r., 1:416; also in l. Am. Chem. Soc., 2:221 (1880~. Laboratory Notes. III. On the preparation of methyl aldehyde. Am. Chem. ~., 1:418; also in Ber. dtsch. chem. Ges., 13:1864 (1880~; J. Am. Chem. Soc., 2:221 (1880~. Laboratory Notes. IV. On the "migration of atoms in the molecule" and Reimer's chloroform aldehyde reaction. Am. Chem. l., 1:420. 1880 Aethylsenfolbildung. Ber. dtsch. chem. Ges., 13: 1866. With L. M. Norton. On ~- and ,8-monobromcrotonic acids. Am. Chem. i., 2:11. With C. Gundelach. Preliminary note on the synthesis of methyl- conine and constitution of conine. Am. Chem. i., 2:171. Darstellung von Methylaldehyd. J. Am. Chem. Soc., 2:221. 1881 With C. Gundelach. Vorlaufige Notiz uber die Synthese des Methyl- coniins und die Constitution des Coniins. Ber. dtsch. chem. Ges., 14:110. Uber die Einwirkung von aromatischen Oxysauren auf Phenole. Ber. dtsch. chem. Ges., 14:656. With L. M. Norton. Uber cY- und ,8-Monobromcrotonsaure. Ber. dtsch. chem. Ges., 14:1202. Uber die Synthese des Methylarbutins. 14:2097. Zur Kenntniss des p-Coniins. Ber. dtsch. chem. Ges., Ber. dt.sch. chem. Ges., 14:2105. 1882 Uber die Synthese des Salicins und des Anhydrosalicylglucosids. Ber. dtsch. chem. Ges., 15:1922.

ARTHUR MICHAEL 1883 351 On the action of aromatic oxy-acids on phenols. Am. Chem. l., 5:81; also in Ber. dtsch. chem. Ges., 16:2298. With A. M. Comey. On some properties of phenylsulphonacetic ethers. Am. Chem. i., 5:116; also in Ber. dtsch. chem. Ges., 16:2300. Synthetical researches in the glucoside group. Am. Chem. I., 5: 171. With A. Kopp. On the formation of crotonic and ,B-oxybutyric aldehydes from ethyl aldehyde. Am. Chem. I., 5:182; also in Ber. dtsch. chem. Ges., 16:2501. Laboratory Notes. V. On the action of sodium ethyl oxide on brom- ethylidenebromide. chem. Ges., 16:2499. Am. Chem. i., 5: 192; also in Ber. dtsch. Laboratory Notes. VI. A new synthesis of allantoin and some sug- gestions on the constitution of uric acid. Am. Chem. I., 5:198; also in Ber. dtsch. chem. Ges., 16:2506. Laboratory Notes. VII. On a convenient method for preparing bromacetic acid. Am. Chem. I., 5:202; also in Ber. dtsch. chem. Ges., 16:2502. Laboratory Notes. VIII. On several cases of intermolecular re- arrangement. Am. Chem. l., 5:203. Laboratory Notes. IX. On a new synthesis of cinnamic acid. Am. Chem. l., 5:205. With A. M. Comey. On the action of aldehydes on phenols. II. Am. Chem. I., 5:349. Laboratory Notes. X. Some convenient quantitative lecture appa- ratus. Am. Chem I., 5:353. Laboratory Notes. XI. Observations on the action of acetylchloride and acetic anhydride on corn and wheat starch. Am. Chem. l., 5:359. On the constitution of resocyanin. 1884 Am.Chem.~., 5:434. With G. M. Palmer. On the action of sodium phenylsulphinate on methylene iodide. Am. Chem. I., 6:253. With G. M. Palmer. On the conversion of organic isocyanates into mustard oils. Am. Chem. I., 6:257.

352 BIOGRAPHICAL MEMOIRS Synthetical researches in the glucoside group. III. Am. Chem. J., 6:336. With J. F. Wing. On the action of methyl iodide on asparagine. Am. Chem. l., 6:419. 1885 With G. \1. Palmer. On some properties of phenylsulphonacetic ethers. II. Am. Chem. i., 7:65. With i. F. Wing. Note on the constitution of the addition-product of chlorhydric acid to ethylcyanide. Am. Chem. J., 7:71. On the decomposition of cinchonine ' Chem. [., 7:182. by sodium ethylate. Am. With G. M. Palmer. On simultaneous oxidation and reduction by means of hydrocyanic acid. Am. Chem. l., 7: 189. With l. F. Wing. On the action of alkyl iodides on amido acids. Am. Chem. J., 7:195. With G. NI. Palmer. On resacetophenone. Am. Chem. i., 7:275. With J. F. Wing. On inactive aspartic acid. Am. Chem. .T-, 7:278. 1886 .. ·— Uber einen Zusammenhang zwischen Anilidbildung und der Consti- tution ungesattigter, mehrbasischer, organischer Sauren. Ber. dtsch. chem. Ges., 19: 1372. .. . With G. M. Palmer. Uber einen Zusammenhang zwischen Anilid- bildung und der Constitution ungesattigter, Mehrbasischer, organischer Sauren. IT Rer ritsch rE`~m f~ec 1q 187\ Uber die einwirkung des Anilins auf die Brommalein- und Chlo~ fumarsaure. Ber. dtsch. chem. Ges., 19:1377. With G. M. Browne. Zue Isomerie in der Zimmtsaurereihe. Ber. dtsch. chem. Ges., 19: 1378. Zue isomerie in der Fettreihe. Ber. dtsch. chem. Ges., 19:1381. Uber die Nitrirung des Phenylhydrazins. Ber. dtsch. chem. Ges., 19:1386. With i. P. Ryder. Zur Kenntniss der Einwirkung von Aldehyden auf Phenole. Ber. dtsch. chem. Ges., 19:1388. Die Citraconsaure als Reagenz zur Erkennung und Scheidung der Aromatischen Amine. Ber. dtsch. chem. Ges., 19:1390. With G. M. Browne. Uberfuhrung der ~-Bromzimmtather in Benzoylessigather. Ber. dtsch. chem. Ges., 19:1392. Einwirkung von Phosphorpentachlorid auf einige organische Ver-

ARTHUR MICHAEL 353 bindungen. Gesellschaft deutscher Naturforscher und Arzte. Tageblatt Naturforsch-Versammlung zu Berlin, 411. 1887 ·— Uber eine bequeme Darstellungsweise von bromirten Fettsauren. [. prakt. Chem., 35:92. Das Verhalten von Essi~saure und eini~en Derivaten derselben gegen ·— ~ O Funffach-chlorphosphor. l. pral~t. Chem., 35:95. , Uber die Constitution der Trimethylentricarbonsaure. l. prakt. Chem., 35: 132. Uber die Bildung des Indigblau aus Orthonitrophenylpropiolsaure mittelst Cyankalium. {. prakt. Chem., 35:254. With G. M. Browne. Uber alloisomerie in der Crotonsaurereihe. i. prakt. Chem., 35:257. ·— Uber die Addition von Natriumacetessig- und Natriummalon- saureather zu den Athern ungesattigter Sauren. i. prakt. Chem. 35: 349; also in Am. Chem. l., 9: 112. Die Reduction von alpha- und alloalphabromzimmtsauren zu Zimmtsaure. ~. prakt. Chem., 35:357. With G. M. Browne. Uber aromatische Hydroxylamine. l. prakt. Chem., 35:358. On some new reactions with sodium acetacetic and sodium malonic ethers. Am. Chem. l., 9:124; also in l. prakt. Chem., 35:449. With J. P. Ryder. On the action of aldehydes on phenols. III. Am. Chem. J., 9: 130. .. Uber das Verhalten von Oxalsaureather zu Resorcin. J. prakt. Chem., 35:510. Bemerkungen zu einer Abhandlung des Hrn. L. Claisen. Ber. dtsch. chem. Ges., 20:1572. Researches on alloisomerism. I. A relation between the constitution of polybasic unsaturated organic acids and the formation of their anilides. Am. Chem. }., 9:180. With G. \~. Palmer. Researches on alloisomerism. II. Am. Chem. J., 9:197. On the action of phosphorus pentachloride on the ethers of organic acids, and on some derivatives of acetic acid. Am. Chem. ~., 9:205. On the action of phosphorus pentachloride on acetanilide. Chem. J., 9: 2 1 7; also in J. prakt. Chem. 35: 207. Preliminary notes. Am. Chem. ~., 9: 219. Am.

354 BIOGRAPHICAL MEMOIRS Antwort auf eine Bemerkung von L. Claisen. {. prakt. Chem., 36:113. With G. \~. Browne. 9:274. With G. M. Browne. prakt. Chem., 36: 174. Remarks on the constitution of levulinic and maleic acids. Am. Chem. J., 9:364. Researches on alloisomerism. Am. Chem. l., Zur isomerie in der Crotonsaurereihe. J. 1888 Preliminary notes on the constitution of sodium acetacetic and malonic esters. Am. Chem. {., 10:158. Uber das verhalten von Natriummalonather gegen Resorcinol. {. prakt. Chem., 37:469. Zur constitution des Natriumacetessigather. l. prakt. Chem. 37:473. With H. Pendleton. Zur Alloisomerie in der Krotonsaurereihe. J. prakt. Chem., 38:1. Zur kritik der Abhandlung von J. Wislicenus: "Uber die raumliche Anordung der Atome in organischen Molekulen." J. prakt. Chem., 38:6. 1889 Bemerkung zu der Abhandlung von J. Wislicenus: "Zur geome- trischen Constitution der Krotonsauren und ihrer Halogen- substitutionsprodukte." ~. prakt. Chem., 40:29. With H. Pendleton. Zu Alloisomerie in der Zimmtsaurereihe. J. prakt. Chem., 40:63. With P. Freer. Uber die einwirkung von Jodwasserstoffsaure auf die Krotonsauren. l. prakt. Chem., 40:95. Uber die Regelmassigkeiten bei der Anlagerung von Halogenver- bindungen an ungesattigte Sauren. J. prakt. Chem., 40:171. 1890 Bemerkung zu d~er Abhandlung von Otto und Rossing uber die Ersetzbarkeit des Natriums in Natriumphenylsulfonessigather durch Alkyle. Ber. dtsch. chem. Ges., 23:669. Bemerkungen zu der Abhandlung von Goldscl~midt und Meissler uber "Versuche zur Constitutionsbestimmung tautomerer Ver- bindungen." J. prakt. Chem., 42: 19.

ARTHUR MICHAEL 355 1891 With P. C. Freer. Uber die Addition von Natriumacetessig- und Natriummalonsather zu den Athern ungesattigter Sauren. II. J. prakt. Chem., 43:390. With O. Schulthess. Untersuchungen uber Alloisomerie. I. Zur Kenntnis der Halogenentziehung bei organischen o~-,8-Halo- gensaureathern. l. prakt. Chem., 43:587. Zur Kenntnis der Lavulinsaure und des Acetondiessigsauredilaktons. t. prakt. Chem., 44:113. Bemerkung zu der Abhandlung von Ad. Claus: uber die Umsetzung von Dibrombernsteinsaureester mit Zink. l. prakt. Chem., 44:399. With G. Tissot. Zur Kenntnis der Homologen der Apfelsaure. Ber. dtsch. chem. Ges., 24:2544. 1892 On the constitution of sodium aces-acetic ether. 14:481. With O. Schulthess. Am. Chem. J., Uber die Addition von Natriumacetessig- und ·— Natriummalonsaureather zu den Athern ungesattigter Sauren. J. prakt. Chem., 45:55. Zur Konstitution des Natriumacetessigather. 45:580; 46:189. ·e Untersuchungen uber Alloisomerie. II. Tul. I. Uber die Addition von Brom zu Acetylendicarbonsaure und deren Athylather. J. prakt. Chem., 46:209. With C. C. Maisch. Uber die Einwirkung von Natriumathylat auf Dibrombernsteinsaureather. i. prakt. Chem., 46:233. M7ith O. Schulthess. Untersuchungen uber Alloisomerie. II. III. Uber die Crotonsaure und Derivate derselben. J. prakt. Chem., 46:236. Untersuchungen uber Alloisomerie. II. IV. Uber die Bildung von fester Crotons~iure bei der Reduktion von allo-c~-Brom- und -chlorcrotonsaure. l. prakt. Chem., 46:266. With G. Tissot. Untersuchungen uber Alloisomerie. II. VI. Beitrage zur Kenntniss einiger Homologen der Apfelsaure. J. prakt. Chem., 46:285. With G. Tissot. Untersuchungen uber Alloisomerie. II. VII. Uber J. prakt. Chem.,

356 BIOGRAPHICAL MEMOIRS die Addition von Chlor zu mehrbasischen ungesattigten Fett- sauren. l. prakt. Chem., 46:381. Untersuchungen uber Alloisomerie. II. VIII. Vergleich der Ver- suchsergebnisse mit den theoretischen Folgerungen aus den Hypothesen Le Bel-Van't Hoff und Wislicenus. 46:400. J. prakt. Chem., Untersuchungen uber Alloisomerie. II. IX. Die van's Hoff'sche Hypothese in ihrer Anwendung auf die Gegenseitegen Bezie- hungen gesattigter und ungesattigter Fettsauren. t. prakt. Chem., 46:424. 1893 Untersuchungen uber Alloisomerie. [. prakt. Chem., 47:197. ·— Uber die Einwirkung von Diazobenzolimid auf Acetylendicarbon- sauremethylester. J. prakt. Chem., 48:94. 1894 ·— Uber die Addition von Natriumacetessig- und reather zu den Athern ungesattigter Sauren. 49:20. Natriummalonsau- J. prakt. Chem., Beitrage zur Kenntnis des Ringbildung bei organischen, stickstoff- haltigen Alerbindungen. J. prakt. Chem., 49: 26. .— Uber die Einwirkung von Natriummalonathylester auf Benzalace- ton. Ber. dtsch. chem. Ges., 27:2126. With G. Tissot. Uber die Brommesakonsaure. Ges., 27:2130. 1895 Ber. dtsch. chem. Zur Schmelzpunktbestimmung von hochschmelzenden und soge- nannten unschmelzbaren organischen Verbindungen. Ber. dtsch. chem. Ges., 28:1629. Uber die Addition von Schwefel zu ungesattigten organischen Ver- bindungen. Ber. dtsch. chem. Ges., 28:1633. With J. E. Bucher. Uber die Einwirkung von Essigsaureanhydrid auf Sauren der Acetylenreihe. Ber. dtsch. chem. Ges., 28:2511. Untersuchungen uber Alloisomerie. III. {. prakt. Chem., 52:289. With T. H. Clark. Relative Leichtigkeit der Kohlendioxydab- spaltung aus den Silversalzen der ,8-Chlorcrotonsauren. l. prakt. Chem., 52:326. With G. Tissot. Dritter abschnitt. l. prakt. Chem., 52:331.

ARTHUR MICHAEL 357 Vierter abschnitt: uber die gesetze der Alloisomerie und Anwen- dung derselben zur Classificirung ungesattigter organischer Ver- bindungen. l. prakt. Chem., 52:344. Bemerkungen zu Arbeiten von C. A. Bischoff, ~. A. Wislicenus and t. H. van's Hoff. J. prakt. Chem., 52:365. 1896 Uber die Einwirkung von Athyljodid und Zinc auf ~-Fettester. Ber. dtsch. chem. Ges., 29:1791. With l. E. Bucher. Zur Constitution der Oxalessigsaure. Ber. dtsch. chem. Ges., 29:1792. Zur Kenntniss der Additionsvorgange bei den Natriumderivaten von Formyl- und Acetessigestern und Nitroathanen. Ber. dtsch. chem. Ges., 29:1793. Herrn. E. Erlenmeyer und C. Liebermann zur Erwiderung. l. prakt. Chem., 54:107. 1898 With l. E. Bucher. On the action of acetic anhydride on phenyl- propiolic acid. Am. Chem. J., 20:89. With F. Luehn and H. H. Higbee. On the formation of imido- 1,2-diazol derivative from aromatic azimides and esters of ace- tylenecarboxylic acids. Am. Chem. i., 20:377. Uber das Verhalten von Benzaldehyd gegen Phenol. l. prakt. Chem., 57:334. 1899 Uber die Ersetzung des Natriums in Natriumphenylsulfonessigester durch Alkyle. J. prakt. Chem., 60:96. Uber einige Gesetze und deren Anwendung in der organischen Chemie. I. [. prakt. Chem., 60:286. With V. L. Leighton. Uber einige Gesetze und deren Anwendung in der organischen Chemie. II. J. prakt. Chem., 60:409. With W. T. Conn. On chlorine heptoxide. Am. Chem. i., 23:444. 1900 Zur Kenntniss der Natriumacetessigestersynthese und der Vierring- bildung mittels Natriumathylats. Ber. dtsch. chem. Ges., 33: 3731.

358 BIOGRAPHICAL MEMOIRS 1901 With W. T. Conn. On the behavior of iodine and bromine toward chlorine heptoxide and perchloric acid. Am. Chem. T.. 25:89. Zur Kenntniss der Perkin'schen Reaction. 34:918. ~ , Ber. dtsch. chem. Ges., On methyl cyanide as a catalytic reagent and a criticism of i. U. Nef's views on the Frankland-Wurtz- and Conrad reactions. Am. Chem. T., 25:419. With V. L. Leighton and F. D. Wilson. Uber die isomeren Iso- butylenchlorhydrine und die Zersetzung der gemischten Aether durch Halogenwasserstoff. .T- prakt. Chem., 64:102. Zur Kenntniss der drei stereomeren Zimmtsauren. Ber. dtsch. chem. Ges., 34:3640. With W. W. Gerner and W. H. Graves. Zur Kenntniss der Sub- stitution-vorgange in der Fettreihe. Ber. dtsch. chem. Ges., 34:4028. ·e Uber einige Laboratoriumsapparate. Ber. dtsch. chem. Ges., 34: 4058. With T. H. Mighill. Zur Kenntniss des Additions-Abspaltungs- Gesetzes. Ber. dtsch. chem. Ges., 34:4215. 1903 Bemerkung zur der Mittheilung des Hrn. S. Svoboda "Uber einen abnormalen Verlauf der Michael'schen Condensation." Ber. dtsch. chem. Ges., 36:763. With W. W. Garner. Beitrage zur Frage der Isozmutsaure. Ber. dtsch. chem. Ges., 36:900. Zur Geschichte der Isozimmtsaure. Ber. dtsch. chem. Ges., 36:2497. On the condensation of oxalic ethylester with ethylene and tri- methylene cyanides. Am. Chem. i., 30:156. Valenzhypothesen und der Verlauf chemischer Vorgange. i. prakt. Chem., 68:487. With V. L. Leighton. Uber die Konstitution des Phenylcinna- menylakrylsauredibromids. J. prakt. Chem., 68:521. 1905 Phenylisocyanat als Reagens zur Feststellung der constitution tauto- merer Verbindungen. Ber. dtsch. chem. Ges., 38:22.

ARTHUR MICHAEL ~q ·. With O. Eckstein. Uber die Bildung von o-Acylderivaten aus Cyanessigester durch Anwendun~ von Pvridin und Chinolin. Ber. dtsch. chem. Ges., 38:50. O , Zur Geschichte der Theorie uber die Bildung und Constitution des Natracetessigesters. Ber. dtsch. chem. Ges., 38:1922. Zur Kenntniss der Synthesen mit Natracetessigester. Ber. dtsch. chem. Ges., 38:2096. Zur Frage uber der Verlaug der Claisen'schen Zimmtsaurestersyn- these. Ber. dtsch. chem. Ges., 38:2523. Zur Kenntniss der Vorgange bei der Synthesen mit Natrium Malonester und verwandten Verbindungen. Ber. dtsch. chem. Ges., 38:3217. Herren Stormer und Kippe zur Erwiderung. Ges., 38:4137. Ber. dtsch. chem. Uber die Darstellung reiner Alkylmalonester. t. prakt. Chem., 72:537. 1906 On the isomerism and tautomerism question. 201. Am. Chem. J., 35: With H. D. Smith and A. Murphy, in The question of isomerism and tautomerism. Ber-. dtsch. chem. Ges., 39:203. Zur constitution des Tribenzoylenbenzols. Ber. dtsch. chem. Ges., 39:1908. With W. W. Garner. Cinnamylideneacetic acid and some of its transformation products. Am. Chem. l., 35:258. With W. W. Garner. Magnesium permanganate as an oxidizing agent. Am. Chem. l., 35:267. Zur constitution des "Kohlensuboxyds." Ber. dtsch. chem. Ges., 39:1915. Uber das Vertheilungsprincip. Ber. dtsch. chem. Ges., 39:2138. Uber den Verlauf der addition von Wasser an Hexin-2. Ber. dtsch. chem. Ges., 39:2143. With R. N. Hartman. Zur Constitution des aus Mannit-Hexen dargestellten Hexylalkohols. Ber. dtsch. chem. Ges., 39:2149. Uber die Einwirkung von Chlor auf Hexan. Ber. dtsch. chem. Ges., 39:2153. With V. L. Leighton. Uber die Addition von Unterchloriger saure an Isobuten. Ber. dtsch. chem. Ges., 39:2157. With F. D. Wilson. Uber den Verlauf der Zersetzung von gemi-

360 BIOGRAPHICAL MEMOIRS schten Fettathern durch ~odwasserstoffsaure. Ber. dtsch. chem. Ges., 39:2569. Uber die Einwirkung von Salzsaure auf Propenoxyd und Propen- alkohol. Ber. dtsch. chem. Ges., 39:2785. Uber die Einwirkung von Salzsaure auf With V. L. Leighton. Isobutenoxyd. Ber. dtsch. chem. Ges., 39:2789. With A. B. Lamb. The isomerism of ethyl coumaric and ethyl coumarinic acids. Am. Chem. l., 36:~52. 1907 With R. N. Hartman. Zur Konstitution des aus Mannit darge- stellten Hexyljodids. Ber. dtsch. chem. Ges., 40: 140. With H. Hibbert. On the ammonia reaction as a means of dis- tinguishing between enol and keto derivatives. I. Ber. dtsch. chem. Ges., 40:4380. With H. Hibbert. The ammonia reaction as a means of distin- guishing between enol and keto derivatives. II. Ber. dtsch. chem. Ges., 40:4916. Die van's Hoff-Wislicenusache Chem., 75: 105. Konfigurationslehre. .T. prakt. 1908 Stereoisomerism and the law of entropy. Am. Chem. .~., 39:1. VVith H. D. Smith. The addition of halogens to cinnamic acid and some of its derivatives. Am. Chem. J., 39:16. Uber Desmotropie und Merotropie. I. Ann. Chem., 363:20. With H. D. Smith. II. Die tertiaren Amine als Reagentien zur Unterscheidung zwischen stabilen Enol- und Ketonderivaten. Ann. Chem., 363:36. With P. H. Cobb. III. der Constitution Merotropen Vergindungen. Ann. Chem., 363:64. With A. Murphy, Jr. IV. Acetylchlorid und Essigsaureanhydrid als Reagentien zur Unterscheidung zwischen Enol- und Keton- derivaten. Ann. Chem., 363:94. Phenylisocyanat als Reagens zur Festellung With W. W. Garner. Magnesium permanganate as an oxidizing agent. Monatshefte fuer Chemie und Verwandte Teile Anderer Wissenschaften, 22:556. With.J. E. Bucher. Zur Frage uber die Festellung der Konstitution

ARTHUR MICHAEL 361 der Phenylnaphthalindicarbonsaure; Hrn. Hans Stobbe zur Antwort. Ber. dtsch. chem. Ges., 41:70. ·. Uber refraktometrischen Beweis der Konstitution des "Kohlen- suboxyds." Ber. dtsch. chem. Ges., 41:925. With H. Hibbert. Uber die vermeintliche Beziehung zwischen Dielektrizitatskonstante und isomerisierender Kraft organischer Losungsmittel bei Enol-Keton-Desmotropen. Ber. dtsch. chem. Ges., 41:1080. ·— With O. D. E. Bunge. Uber den stereochemischen verlauf der Addition von Chlor zu Crotonsaure. Ber. dtsch. chem. Ges., 41:2907. 1909 With H. Hibbert. V. Zur Constitution des Cyanwasserstoffs. Ann. Chem., 364:64. With H. Hibbert. VI. Zur Constitution der Cyansaure. Ann. Chem., 364:129. With R. F. Brunel. On the relative ease of addition in the alkene group. First paper on the laws of addition in organic chemistry. Am.Chem. [.,41:118. Zur theorie der Esterfikation organischer Carbonsauren. (Erste Mitteilung uber die Natur der "sterischen Hinderung"~. Ber. dtsch. chem. Ges., 42:310. ·— With K. ~. Oechslin. Uber den Einfluss der substituenten aro- matischer Carbonsauren auf ihre Esterifikation. II. Ber. dtsch. chem. Ges., 42:317. Das chinon von Standpukt des Entropiegesetzes und der Partialva- lenzhypothese. T. prakt. Chem., 79:418. ·. With K. Wolgast. Uber die Beziehung zwischen Struktur des Fet- talkohole und Geschwindigkeit der Esterifikation. III. Ber. dtsch. chem. Ges., 42:3157. With K. ~rolgast. Zur Darstellung reiner Ketone mittels Acetes- sigester. Ber. dtsch. chem. Ges., 42:3176. 1910 .— Uber die Beziehung zwischen Structure der Fettalkohole- und geschwindigkeit der Esterifikation. Ber. dtsch. chem. Ges., 43:464. .. Uber die "Additionstheorie," Hrn. S. l. Acree zur antwort. Ber. dtsch. chem. Ges., 43:621.

362 BIOGRAPHICAL MEMOIRS On the application of physical chemical methods to determine the mechanism of organic reactions. Am. Chem. I., 43:322. Outline of a theory of organic chemistry founded on the law of entropy. J. Am. Chem. Soc., 32:990. With A. Murphy, in On the action of chlorine in solution in car- bon tetrachloride and of carbon tetrachloride on metallic oxides. Am. Chem. I., 44:365. With P. H. Cobb. Uber die Reaktion zwischen Chinon und Salz- saure. I. prakt. Chem., 82:297. Uber den Mechanismus der Chinonreaktionen. Hrn. Theodor Posner zur erwiderung. I. prakt. Chem., 82:306. 1911 With H. Leupold. Zum verlauf der intramolekularen Umlagerun- gen bei den Alkylbromiden und zur Frage der Ursacl~e des Gieichgewichtszustandes bei Unkehrbaren reaktionen. Ann. Chem., 379:263. 1912 With R. F. Brunel. Action of aqueous solutions of acids on alkenes. Am. Chem. i., 48: 267. With F. Zeidler. Chemistry of the amyl series. Ann. Chem., 385: 227. Number of isomers in merotropic and desmotropic compounds. I. Ann. Chem., 390:30. Number of isomers in merotropic and desmotropic compounds. II. Isomeric keto forms of acetyldibenzoylmethane. Ann. Chem., 390:46. \Vith Harold Hibbert. Number of islanders in merotropic and des- motropic compounds. III. Isomeric keto forms of propionyl- dibenzoylmethane. Ann. Chem., 390:68. Number of isomers in merotropic and desmotropic compounds. IV. Isomeric forms of formylphenylacetic ester. Ann. Chem., 391: 235. With G. P. Fuller. Number of isomers in merotropic and des- motropic compounds. Isomeric enol forms of formylphenylacetic ester. Ann. Chem., 391:275. With F. Zeidler. Course of intramolecular rearrangements in alkyl bromides. Ann. Chem., 393:81.

ARTHUR MICHAEL 363 Application of the "scale of combined influence" to explain the ioni- zation constants of organic acids, and a reply to C. G. Derik. i. Am. Chem. Soc., 34:849. 1913 The Perkin reaction. Am. Chem. i, 50:4 1 1 . ·— With E. Scharf. Uber den Mechanisms der Einwirkung van Brom auf Fettsaurechloride. Ber. dtsch. chem. Ges., 46:135. 1914 With W. Schlenk, l. Appenrodt and A. Thal. Uber Metalladi- tionen en mehrfache Bindungen. Ber. dtsch. chem. Ges., 47:473. Number of isomers of merotropic and desmotropic compounds. VI. Isomeric forms of formylphenylacetic ester. Ann. Chem., 406:137. 1916 With E. Scharf and K. Voigt. Rearrangement of iso into tertiary butyl bromide. l. Am. Chem. Soc., 38:653. 1918 Configurations of organic compounds and their relation to chemical and physical properties. I. Am. Chem. Soc., 40:704. Configurations of organic compounds and their relation to chemical and physical properties. II. The relations between the physical properties and the configurations of unsaturated acids. J. Am. Chem. Soc., 40: 1674. 1919 Relations between the chemical structures of carbonyl derivatives and their reactivities towards salts of semicarbazide. J. Am. Chem. Soc., 41:393. 1920 The chemical mechanism of organic rearrangements. Soc., 42:787. J. Am. Chem. The non-existence of valence and electronic isomerism in hydroxyl- ammonium derivatives. i. Am. Chem. Soc., 42:1232.

364 BIOGRAPHICAL MEMOIRS 1921 The structures and reactions of hydroxylamine and its derivatives. I. i. Am. Chem. Soc., 43:315. 1929 Castor-oil preparation. Australian patent 20,127. 1930 With l. Ross. Course of addition of sodium enol alkyl malonic esters to c~,,8-unsaturated esters. I. Am. Chem. Soc., 52:4598. 1931 With I. Ross. Course of addition of sodium enol alkylmalonic and sodium enol alkylcyanoacetic esters to unsaturated esters. I. Am. Chem. Soc., 53:1150. With i. Ross. c~,3^y-Trimethylglutaric acids. l. Am. Chem. Soc., 53:1175. With J. Ross. Partition principles as applied to the structures of enolic sodium derivatives of 1,3-diketones and ,8-keto esters. [.Am. Chem. Soc., 53:2394. 1932 With l. Ross. Partition principles as applied to the structure of enolic sodium derivatives of 1,3-diketones and ,B-keto esters. II. J.Am.Chem.Soc., 54:387. With i. Ross. Addition of sodium enol alkylmalonic ester to benzal- acetophenone. T. Am. Chem. Soc., 54:407. 1933 With I. Ross. Course of addition of the sodium enolates of malonic and methylmalonic esters to benzalacetophenone and to crotonic ester. I. Am. Chem. Soc., b5: 1632. With l. Ross. Carbon syntheses with malonic and related acids. 1. i. Am. Chem. Soc., b5: 3684. 1934 With N. Weiner. Formation of enolates from a-lactonic esters. l. Am. Chem. Soc., 56:2012.

ARTHUR MICHAEL 1935 365 With G. H. Carlson. Mechanism of reactions of acetoacetic ester, the enolates and structurally related compounds. I. C- and O- Alkylation. i. Am. Chem. Soc., 57:159. The mechanism of the reactions of metal enol acetoacetic ester and related compounds. II. Sodium enolates toward acyl chloride. I. Am. Chem. Soc., 57:165. With G. H. Carlson. Mechanism of the nitration process. l. Am. Chem. Soc., 57:1268. 1936 \Vith N. Weiner. Mechanism of the sulfonation process. T. Am. Chem. Soc., 58:294. I\Iechanism of the reactions of metal enol acetoacetate ester and related compounds. III. Copper enolates. T. Am. Chem. Soc., 58:353. \\lith N. Weiner. Carbon syntheses with malonic acid and related compounds. II. Aromatic aldehydes.~ I. Am. Chem. Soc., 58:680. With N. Weiner. Formation of enolates from lactonic esters. l. Am. Chem. Soc., 58:999. 1937 With N. Weiner. 1,2- and 1,4-Addition. I. The 1,4-addition of potassium isocyanate. I. Am. Chem. Soc., 69:744. With G. H. Carlson. 1,2- and 1,4-Addition. II. Nitrogen tetroxide and trimethylethylene. l. Am. Chem. Soc., 59:843. Course of the addition of malonic enolates to a,,8-unsaturated esters. J. Org. Chem., 2:303. 1938 \Vith N. Weiner. The partition principle as applied to the struc- tures of enolic sodium derivatives of ,8-diketones and ,8-keto esters. III. l. Org. Chem., 3:372. 1939 With G. H. Shadinger. Influence of solvents on the stereochemical course of the addition of hydrogen bromide to monobasic acety- lenic acids and the relation of solvent effect to chemical structure. I. Org. Chem., 4:128.

366 BIOGRAPHICAL MEMOIRS With G. H. Carlson. 1,2- and 1,4-Addition. III. Nitrogen trioxide and trimethylethylene. I. Org. Chem., 4:169. The relations of "oxygen and peroxide effect," and of hypochlorous acid addition, to the structures of unsaturated organic com- pounds. I. Org. Chem., 4:519. With N. Weiner. Solvent and peroxide effect in the addition of hydrogen bromide to trimethylethylene. I. Org. Chem., 4:531. 1940 With G. H. Carlson. 1,2- and 1,4-Addition. IV. Nitrogen tetroxide and isobutylene. I. Org. Chem., 5: 1. \Vith G. H. Carlson. 1,2- and 1,4-Addition. V. Nitrogen tetroxide and tetramethylethylene. l. Org. Chem., 5:14. With N. Weiner. Solvent and peroxide effect in the addition of hydrogen bromide to unsaturated compounds. IV. Isopropyl- ethylene. I. Org. Chem., 5:389. 1943 With C. M. Saffer, fir. The addition of triphenylmethylsodium and phenyllithium to cinnamic ester and benzalacetophenone. J. Org. Chem., 8:60. With H. S. Reason. Normal addition of hydrogen bromide to 3- butenoic, 4-pentenoic and 5-hexenoic acids in hexane. I. Am. Chem. Soc., 65:683. With H. S. Mason. Determination of the composition of mixtures of c'-bromo-c'-methyl, and cY-bromo-,8-methylsuccinic acids. l. Org. Chem., 9:393.