ULLETIN OF THE UNIVERSITY OF WISCONSIN NO. 528 i j Science Series, Vol. 4, No. s, pp. izs-m THE CLASSIFICATION OF CARBON COMPOUNDS BY EDWARD KREMERS, Ph.D. Professor of Pharmaceutical Chemistry The University of Wisconsin CONTRIBUTIONS FROM THE COURSE IN PHARMACY MADISON, WISCONSIN 1912 Reprinted 1924 Price, $1.00 table of contents 54-7 Kztc. (LO p* *2-* & Preface 5 O Definition of organic chemistry 7 O History of chemical organic classification 10 A rational system of the classification of carbon compounds based on their structure 17 Classification of the hydrocarbons 17 Kekule’s structural considerations based on the quadrivalence of the carbon atom 17 The limit formula of saturation and formulae of lesser satu- ration; degrees of saturation 18 The structural equivalents of pairs of hydrogen atoms 31 The double bond T 31 The cycle A 31 The treble bond p 31 Table of types of hydrocarbons 31 Table of structural equivalents 31 Classification of the substitution products of the hydrocarbons .... 32 The three simple hydrocarbon groups the basis of simple types 32 Extent of substitution 32 Substitution in connection with the same carbon atom 33 Halogen substitution products 33 Hydroxy substitution products and their dehydration products 34 Amido substitution products and their deammonation products 36 Other substitution products 37 Genetic relationship of types 38 Mono 40 Di 41 Tri 42 Substitution in connection with different carbon atoms 45 Multiplication of types 45 Heterocyclic compounds 48 Containing C, H and O Containing C, H and N [ 131 ] 782292 Digitized by the Internet Archive in 2017 with funding from University of Illinois Urbana-Champaign Alternates https://archive.org/details/classificationofOOkrem PREFATORY REMARKS “Arbeit allein kann die Licht gebenden Ideen nicht herbeizwin- gen. Etwas vom Schauen des Dichters muss auch der Forscher in sich tragen.” Helmholtz. “La science ne consiste pas en faits, mais dans les consequences que l’on en tire.” At the annual meeting of the Wisconsin Academy of Sciences, Arts, and Letters in December, 1894, the writer read a paper “On the Classification of Carbon Compounds,” which was pub- lished in the Transactions 1 of that body. The introductory paragraph may here be quoted: “In the winter semester of 1888-9, Professor August Kekuld, in his course on the chemistry of the carbon compounds at the University of Bonn, Germany, introduced the subject of fatty al- cohols, aldehydes, ketones, acids, hydroxy acids, etc., by a lec- ture in which he gave a general survey of the theoretically pos- sible hydroxy derivatives of the paraffin hydrocarbons. I sup- pose it was Prof. Kekul4’s usual method of treating the sub- ject, but I am not warranted in making so broad a statement. However, this theoretical introduction is fully in harmony with the methods of teaching of this genial lecturer, known and cele- brated not so much for the compounds he has discovered, but for 1 Vol. 10, p. 310. A second paper was read ten years later, but not published. At the Baltimore meeting of the American Chemical Society in 1909, a twenty-minute paper on the same subject was read by request at a general meeting of the Association. [ 133 ] 6 BULLETIN OB THE UNIVERSITY OF WISCONSIN his theories, that have prophesied the possibility of hosts of compounds, which have been prepared by others in the attempt to establish as well as in the attempt to overthrow Prof. Kekule’s theories.” If honest confession be good for the soul, the above paragraph ought to suffice to show that the writer makes no great claim for originality and at the same time it reveals the source of his inspiration. All that the writer claims is that he has endeavored to systematize by means of logical questions and answers. The problem of rational classification of the carbon compounds is one of those that can not be worked out in the research lab- oratory, but has to be solved primarily in the class room. Now, that after more than twenty years of experience in this direc- tion the system has revealed its advantages not only in the class room of the writer but in the class rooms of his former students as well, the time seems to have arrived when the more completely worked out system should be given wider publicity. However, while the system had to be tried out in the class- room, the conference, and the seminar, it has found useful appli- cation in laboratory research. As applied to the sesquiterpenes , 2 as representatives of the hydrocarbons, it has evidently proven acceptable to others . 3 In the systematic study of the glucosides, pigments, and alka- loids it has brought out relationships formerly not apparent. An attempt is also being made to make the organic laboratory manual something more than a collection of working formulas, and suggestions for reading. As to details, the writer hopes to find the time to bring the entire materia phytochemica into con- formity with this system and thus to show the numerous practical as well as theoretical advantages which it possesses. It may be suggested that the time is not opportune for a re- vision of the classification of carbon compounds on the basis of structural atomic chemistry, since the atoms are about to be replaced, in chemical thought, by electrons. Such a sugges- tion, however, is not likely to be well received so long as even * O. Schreiner, The sesquiterpenes, p. 17. * Comp. " Neuere Eintheilung der Sesquiterpene” in Arnold Lewinsohn, Beitraege tur Kennlniss der Sesquiterpene, lnnaugural-Dissertation, Leipzig, 1908, p. 14. [ 134 ] KREMERS — THE CLASSIFICATION OF CARBON COMPOUNDS 7 physicists warn chemists “not to be too ready to throw away conceptions (such e. g., as that of an atom) . . . that have proved very valuable as aids to the advancement of science in the past .” 4 However valuable the theory of electrons may prove, it may be a generation or more before it can affect our ideas of the classi- fication of carbon compounds, should it ever exert such an in- fluence. While we should always welcome new tools and learn to use them if possible, it would be foolish indeed to discard an old tool, simply because a new one, which we have not learned to use, is in sight . 6 All that the writer asks for the suggestions toward the rational classification of the carbon compounds is that they be given a fair trial. He fully realizes that in such matters changes are not likely to come about with revolutionary suddenness, but that old habits of thought must be gradually overcome by the slow process of evolution. DEFINITION OF ORGANIC CHEMISTRY For the purpose of this study organic chemistry is defined as the chemistry of the hydrocarbons and their substitution products. Not that this definition covers ground other than that covered by the definition mostly in vogue at the present time, viz., that organic chemistry is the chemistry of the carbon com- pounds, but that the definition suggested has this advantage in the study of classification and nomenclature that it emphasizes two important lines of thought and development. First, it emphasizes the fact that the hydrocarbons, the simplest of car- bon compounds, are to be regarded as basal compounds and that all other carbon compounds are to be derived from these hydro- carbons by the process of substitution. * President Richard G. MacLaurin of Mass. Inst, of Tech, at the banquet of the A. C. S. Science, 32, p. 10. * It would be more than foolish for the accomplished piano player to abandon his instru- ment at the age of twenty-five or more because he has become convinced that the violin is the more perfect musical instrument. While a successful pianist, he might, and, in all probability, would, achieve only mediocrity with the violin. The same reasoning ap- plies to the present day chemist and his possible change from the atomic to the electron theory. [ 135 ] 8 bulletin of the university OF WISCONSIN Kolbe at one time suggested that all carbon compounds be derived from carbon dioxide from which the plant synthesizes its complex carbon compounds. But though we could follow the synthetic processes of the plant much better than we can even today, no one would any longer think of following such a suggestion for purposes of classification or nomenclature. Our knowledge of the hydrocarbons, however, is such that today they universally serve as the basal compounds, not only for purposes of classification and nomenclature but for didactic purposes as well. What we need at present is a more rational classification of these basal hydrides of carbon than is commonly found in organic chemical literature. The second basal thought suggested by the definition is, as al- ready pointed out, that all other carbon compounds be derived from the hydrocarbons by the process of substitution. In re- search work, in preparation work, and also in analytical proc- esses we make extensive use of the additive capacity of com- pounds. We need in no wise underestimate the importance of the ad- dition product because addition is not universally applicable, yet this is more than sufficient reason for not adopting it as a basal process in a system of classification and nomenclature. Neither can we for this purpose adopt advantageously any other than a Unitarian point of view. What we need in organic classifica- tion and nomenclature is to get rid, for the purpose under con- sideration, of points of view based on totally different concep- tions, such as the old dualistic view of acids, bases, and salts, that of the theory of types, etc. The term organic chemistry is said to have been introduced by Bergmann who pointed out that there was no fundamental difference between the chemical compounds from the vegetable and animal kingdoms. Previous to his time the materia chem- ica, and with it chemical science, was divided according to the source of the material from the mineral, vegetable, and animal kingdoms. In this chemists had followed the suggestion by Emanuel, who in 1682 classified all terrestrial objects according to their relation to one of these natural kingdoms. However, organic chemistry was long thereafter still subclassified into vegetable chemistry and animal chemistry. [136] KREMERS — THE CLASSIFICATION OF CARBON COMPOUNDS 9 The student of organic chemistry is usually told that by his so-called synthesis of urea, Woehler in 1828, dealt the death- blow to the notion that organic chemistry is the chemistry of the functions of organs and their products, in other words of that mysterious something called life. Yet Woehler’s so-called synthesis was no synthesis at all, but an inversion, an intra- molecular re-arrangement of the atoms of one molecule to an- other of like size. Neither did Woehler’s noteworthy and far- reaching observations immediately influence chemical thought, at least so far as definition and classification reflected the ad- vance of chemical thought. Even Gmelin stated that “the bodies of the organic kingdom are distinguished in their most complete state, from those of the inorganic kingdom . . . by being composed, for the principal and most important part at least, of chemical compounds quite peculiar to them, called organic compounds . . . ’ n Today we have gotten away completely from any significance of life so far as the concept organic chemistry is concerned. That branch of chemistry which deals with the so-called life processes of plants and animals is termed biochemistry and rep- resents a line of chemical activity as does phytochemistry and zoochemistry. Organic chemistry is universally interpreted at present as implying the chemistry of the carbon compounds irre- spective of source or mode of formation. The term carbon has reference to elemental composition and could not have been used before the recognition of the modern elements since the close of the 18th century. Indeed, its use in the sense as quoted above is of much more recent date. The first to have suggested the definition of organic chemistry as the chemistry of carbon appears to have been Gerhardt as early as 1844 or possibly earlier. 1 2 Kekule then suggested that we “define organic chem- istry as the chemistry of the carbon compounds.” 3 This def- inition-subtitle was accepted by Richter, one of the disciples of Kekul4 and author of the well-known text which has been re- 1 For a more detailed statement see Appendix: Definitions of organic chemistry. * See Appendix: Definitions of organic chemistry. 3 See Appendix: Definitions of organic chemistry. [ 137 ] 10 bulletin of the university OF WISCONSIN peatedly revised by Anschuetz and translated into English by Smith . 4 As a mere definition this will do as well as any other especially if interpreted in the light of Kekule’s commentary , 5 but if our definition is to point logically to the method of classification, as the classification should reflect the most satisfactory chemical theories, then it is no longer satisfactory for purposes such as are here to receive consideration. Hence for our present needs we prefer to define organic chemistry as the chemistry of the hydrocarbons and their substitution products. A careful perusal of the principles of classification will, no doubt, be found to justify the adoption of this definition which is equally valuable from a didactic point of view. HISTORY OF ORGANIC CHEMICAL CLASSIFICATION In order to give proper expression to chemical ideas, a chemi- cal language has been developed which reflects chemical thought. Science, we are told, consists not of fats, but in the conclusions which we draw from them. Some of the most important con- clusions drawn from chemical facts have been derived by sys- tematization of the materia chemica. As a result, general theory and chemical classification have developed side by side, so that the study of the history of classification reflects in no small part the advance made in general chemical theory. A review of the principal systems of classification of the past hundred years and more, clearly reveals the fact that the ra- tional systems of classification were based largely on structural theories, structural of necessity, in the varying sense in which this concept was interpreted from time to time. The temporary breakdown of structural conceptions during the middle of the nineteenth century, when atoms had to give way to equivalents, gave rise to a condition bordering on anarchy not only in classi- 4 Victor von Richter’s Organic Chemistry or Chemistry of the Carbon Compounds. Edited by R. Anschuetz. Authorized translation by E. F. Smith, 1899. •See Appendix: Definitions of organic chemistry. [ 138 ] KREMERS — THE CLASSIFICATION OF CARBON COMPOUNDS 11 fication but in general chemical thought. The arrangement of carbon compounds according to the number of carbon atoms* is no more a rational classification than the arrangement of plants according to the number of the stamens of their flowers. Such an artificial arrangement, while of value in the tracing of ana- lytical results based on elementary analysis * 1 does not afford for most purposes even the convenience of the alphabetical arrange- ment of the chemical dictionary or encyclopedia. Previous to the chemistry of oxygen, as elucidated by Lavois- ier, there was no organic chemistry in name, and but few car- bon compounds had been isolated or prepared artificially. 2 Yet in order to understand later developments, it seems advisable to go back as far as Lemery and one of the first chemical texts free from alchemistic jargon, his Coitrs de ckimie. Following the classification of all natural objects (and beings) into three natural kingdoms, the regna naturae, suggested by Emanuel in 1682, Lemery arranged the subject matter of his Course in Chemistry under these headings: (1) Upon minerals (2) Upon vegetables, and (3) Upon animals. As early as 1780, Bergmann began to distinguish organic from inorganic bodies, having shown that the same organic substances can be obtained from both the vegetable and animal kingdoms. Nevertheless, the classification of the organic materia chemica according to the two kingdoms of organized nature, namely the vegetable and animal was upheld for a long time. Thus Lavoisier, whose principal point of view was that of oxygen first, last, and all the time, separates the carbon-con- taining acids obtained from the vegetable kingdom from those obtained from the animal kingdom. This separation is found even in the third, rewritten and revised edition of Lavoisier’s “Traite eUmentaire de chimie ” of 1801. Fourcroy, one of Lavoisier’s associates on the Commission of Chemical Nomenclature according to the antiphlogistic system, * See Appendix: Arrangement according to number of carbon atoms. 1 Compare Richter’s Lexikon der Kohlenstoff-Verbindungen, and the Formel-register of the Berichte der deutschen chemischen Gesellschaft based on the same principle. 2 See Appendix: Classification as revealed by tables of contents. [ 139 ] 12 bulletin of the university OF WISCONSIN likewise distinguished between “les composes vegetaux ” 3 4 and the “ substances animates.”* Berzelius, the great generalizer of his time, in his epoch-making “Lehrbuch der Chemie” does likewise, even in the third edition published in 1837. His organic chemistry is subdivided into “ Plant Chemistry ” 5 and “ Animal Chemistry .” 6 With such classical examples as guides, it is not surprising that other authors followed even up to the middle of the nine- teenth century. Thus this system of classification long out- lived its theoretical usefulness. Whatever may be said for or against the designation of La- voisier as the founder of chemical science, this much is undeniably true that his antiphlogistic theories placed chemical classification and nomenclature on a new basis. As already pointed out, the chemistry of Lavoisier was the chemistry of oxygen just as the predominant chemistry of Kekul4 and of the generation of chemists that followed him was a chemistry of carbon, even more so. The oxides of the metals were designated bases, the oxides of the nonmetals, acids, both binary compounds, and the union of the two resulted in the ternary compounds or salts which nat- urally also contained oxygen. Thus there was laid the founda- tion for the electrochemical theories of Davy and the dualistic structural theories of Berzelius. The discovery of the halogens and their derivatives naturally modified these views but they did not revolutionize them. Indeed we today are still under the ban of the antiquated theory of acid, base and salt. Compared with the inorganic field, organic chemistry as de- fined by Bergmann played but a minor role though it was being enriched by Scheele and other phytochemists. Yet organic chemistry had its organic acids comparable to the inorganic acids, it also had its inorganic salts of these organic acids. The organic base, however, was wanting until Sertuerner discovered it in morphine, this “new salifyable plant base” as he called it. This morphine attracted universal attention, not because it had been * Systeme des connaissances chimique (Bumaire, An. IX), tomes 7 et 8. 4 Ibidem, tomes 9 et 10. ‘ Vols. 6, 7 and 8 of the 3rd German edition of 1837. 6 Vol. No. 9 of the same edition. [ 140 ] KREMERS — THE CLASSIFICATION OF CARBON COMPOUNDS 13 isolated from opium, for such isolation had been effected inde- pendently by both Derosne and Sertuerner more than a dozen years before, but because Sertuerner had recognized its basic, i. e ., its salt-forming properties. Thus the parallel between organic chemistry and inorganic chemistry was thought to have been established. This satisfaction, however, was of but short duration for chem- ists soon realized the importance of the fact, already hinted at by Sertuerner, that morphine and the alkaloids discovered in rapid succession, were related to the inorganic ammonia, rather than to the oxygen bases of the metals. The conception of this parallel, however, seemed too good to be abandoned, so it was revived by Liebig who pointed out that the organic alcohol was the true analogue of the inorganic base as the organic acid was that of the inorganic oxygen acid. In like manner the product of the union of organic acid and alcohol, the etheral salt or ester, was regarded as the analogue of the inorganic salt. Thus there was re-established the true analogy between organic chemistry and inorganic chemistry, and organic chemistry was defined the chemistry of the compound radicle by Liebig, the alkyl or positive radicle corresponding to the metal, the acyl or negative radical to the non-metal. Whereas the difficulties of the inorganic system were patched up by coining new names, such as halogen acids and halides, thioacids and thionates, the difficulties of the organic field would not be downed by coining such words as neutral principles, i. e., substances that were neutral in themselves and not by virtue of the neutralizing power of acid upon alkali or vice versa . Yet in organic chemistry as in inorganic chemistry we are still la- boring under the ban of opposites, of acids and alcohols, which instead of being regarded primarily as opposites should rather be looked upon as related compounds. The difficulties arising from the ever growing number of car- bon compounds were not solved by creating new classes of com- pounds or by relegating them to an ever convenient lumber chamber. The conception of the rigid radicle, this element, so- called, of organic chemistry, had to be abandoned in the light of the theory of substitution. The concept of homology, though [ 141 ] 14 bulletin of the university OF WISCONSIN it aided materially in throwing light on difficult problems, did not remove the more fundamental difficulties of the situation. Neither did the theory of types, though it, more than any one other conception, aided in bringing order into chaos, and though it paved the way for the structural theories of Kekule. All of these theories and views are reflected in chemical no- menclature and classification. These reflections are found not only in the chemical history of the past century, but in our pres- ent day mode of chemical thought and language. While useful at times, they often linger as an obstructing “spuk” just as the life “spuk” of organic chemistry has made its presence felt again and again and has not been downed completely even today. The manner in which these ideas are reflected in chemical classi- fication can best be seen from the tables of contents of contem- porary treatises on chemistry. The structural conceptions of Kekule are too well known to be reviewed here. How he arrived at them he himself has told us in his after dinner speech of 1890 at the celebration of the twenty- fifth anniversary of the benzene theory. 7 How he worked out his structural or graphic formulas is best shown in some of the considerations of the next chapter. Frankland having recognized the tetravalence of the carbon atom, Kekule added the type methane to the older types am- monia, water, hydrohalogen and hydrogen. The structural con- ception of the hydrocarbons of the methane series and of their halogen and hydroxy substitution products resulted. These, together with the olefine and acetylene hydrocarbons and their respective derivatives were grouped together as fatty compounds. His conception of the structure of benzene added still a new type and its homologues and their derivatives were grouped together as aromatic compounds. Great as was the advance made by Kekule in his classifica- tion there is today no more justification in adhering to it than to the notion of acids and bases. Both conceptions emphasize opposites whereas the relation of gradual evolution is the im- portant point to be emphasized. Opposition becomes apparent 7 Berichte, 23, p. 1306. For an English translation see the Kekule lecture by Jepp in the J. C. S. 73, p. 100 of Transactions. [ 142 ] KREMERS — THE CLASSIFICATION OF CARBON COMPOUNDS 15 only when we take two compounds or classes of compounds out of their natural surroundings and contrast them by ignoring the intervening links. In an age of evolution such a method of procedure is as fundamentally wrong in chemistry as it is in biology. [ 143 ] A PROPOSED BASIS FOR THE RATIONAL CLASSI- FICATION OF CARBON COMPOUNDS CLASSIFICATION OF THE HYDROCARBONS Assuming the tetra-valence of the carbon atom, there is but one hydrocarbon in which all four of the affinities of the carbon atom can be saturated by hydrogen. The four affinities may be indicated in the plane of the printed page by four lines in the I following manner: — C — . If these affinities are saturated by hydrogen we get the formula for methane or marsh gas, CH 4 or H H — C — H. In place of saturating these four affinities with hy- H drogen, or e. g., with halogen or oxygen, it may be assumed that one or more may be satisfied by the same number of valencies of other carbon atoms. Assuming for the present that the car- bon atom be united with other carbon atoms by single affinities only, we get the following carbon nuclei with their free affinities: 18 BULLETIN OP THE UNIVERSITY OP WISCONSIN If these free affinities are now satisfied by hydrogen, the fol- lowing hydrocarbons result: H H I I H— C— C— H I I H H H H H I I I H— C— C— C— H III H H H H H H H I I I I H— C— C— C— C— H -Mil H H H H It will be seen at once, that each carbon atom is united with two hydrogen atoms, and that the two end carbon atoms have a third affinity satisfied by hydrogen. For n carbon atoms there are, therefore, 2n + 2 hydrogen atoms in each molecule. Hence, the general formula for these and like hydrocarbons will be C n H 2n+2 - Having assumed a tetra- valence for the carbon atom this will, therefore, be the limit series of hydrocarbons ( Grenz - kohlenwasserstojje ) . We can imagine but one such series and only one is known. If in place of uniting two carbon atoms of the same molecule by a single bond, we imagine them united by two bonds the fol- lowing carbon nuclei will result: \ / \ I I c=c c=c— c— / V / I \ I / c=c— c— c— If the free affinities be now satisfied by hydrogen atoms the following hydrocarbons are obtained: H H \ / C=C / \ H H H H H \ I I C=C — C — H / I H H H H H H \ I I I C=C— C— C— H / I I H H H The addition of the carbon and hydrogen atoms in each mole- cule will show that these hydrocarbons contain two hydrogen atoms less than the hydrocarbons with the same number of car- bon atoms first developed. Their general formula will, there- fore, be: CnH2n + 2 — H 2 = CnH2n. [146] KREM3RS — THE CLASSIFICATION OF CARBON COMPOUNDS 19 Hence we can derive the hydrocarbons of the formula C n H 2n from the hydrocarbons of the formula C n H 2n -f- 2 by the ab- straction of two hydrogen atoms. This abstraction of hydrogen atoms may take place first of all in connection with neighboring carbon atoms. Thus ch 3 ch 2 — CH 2 1 will yield 1 or II ch. ch,— ch 2 ch 3 ch,— ch 2 1 1 II CH, l will yield CH— or CH 1 ch 3 | ch, j CH, ch 3 ch,— CH, 1 1 II ch 2 1 will yield CH— 1 or CH 1 ch, ch 2 CH, 1 ch, j ch, j CH, CH, l CH 3 1 CH— CH or 1 or II CH— 1 CH ch 3 | CH, ch 3 CH— CH, 1 1 II ch,— ch will yield ch,— c— or ch 3 — c j ch 3 1 ch 3 1 CH, These hydrocarbons are identical with those derived by the previous method. [ 147 ] 20 BULLETIN OB THE UNIVERSITY OB WISCONSIN Secondly, the two hydrogen atoms may be abstracted from carbon atoms that are not neighboring but have one other car- bon atom intervening. In that case ch 3 ch 2 — ch 2 1 ch 2 will yield 1 ch 2 or dH 2 — ch 5 ch 3 ch 2 — ch 3 ch 2 — ch 2 1 ch 2 ch 2 1 will yield 1 or / \ ch 2 CH— CH CH 2 1 1 ch 3 | ch 3 CH S ch 3 ch 2 — 1 ch 2 1 ch 2 ch 2 1 1 / \ ch 2 will yield CH— or CH CH 2 1 ch 2 | ch 2 1 | ch 2 ch 3 ch 3 1 ch 3 If next we allow two carbon atoms to intervene between the carbon atoms from which the hydrogen atoms are abstracted the following cyclic hydrocarbons result: ch 3 ch 2 — ch 2 | ch 2 ch 2 — ch 2 1 will yield 1 or 1 1 ch 2 ch 2 ch 2 — ch 2 1 ch 3 1 ch 2 — ch 3 1 ch 2 — 1 1 ch 2 1 ch 2 ch 2 — ch 2 ch 2 will yield 1 CH 2 or I 1 1 CH— CH 2 1 ch 2 1 CH— 1 ch 3 j ch 3 | ch 3 etc. [ 148 ] KREMERS — THE CLASSIFICATION OF CARBON COMPOUNDS 21 Next we may allow three, four or more carbon atoms to in- tervene and cyclic hydrocarbons with five, six and more members to the cycle will result. Proceeding from normal hydrocarbons of the methane series the following hydrocarbons are obtainable. The* cyclic members are classified according to the number of carbon atoms to the cycle and are tabulated so as to show the isomerism of the hy- drocarbons with the same number of carbon atoms. [ 149 ] 22 bulletin of the UNIVERSITY OF WISCONSIN CnH2n-f 2 ch 4 ch 3 ch 2 1 II ch 3 ch 2 ch 3 1 ch 2 II ch 2 CH ch 2 1 ch 3 1 CH, ch 2 — ch 2 ch 3 ch 2 ch 3 ch 2 1 II 1 / \ ch 2 t CH CH i II CH— CH 2 ch 2 1 1! CH 2 CH | CH, ch 3 | | CH, CH, ch 3 1 ch 2 ch 3 ch 2 ch 2 II 1 / \ / \ ch 2 1 CH CH 1 II CH— CH 2 CH— CH ch 2 1 1 II ch 2 ch | ch 2 | | CH, CH, ch 2 1 1 ch 2 ch 2 1 CH, ch, ch, ch, ch 3 ch 2 ch 3 ch 3 ch 2 ch 2 1 II 1 1 / \ / \ ch 2 1 CH CH CH 2 1 II 1 CH,CH CH 1 I il CH— CH 2 CH— CH ch 2 1 | ch 2 1 CH 2 CH, ch 2 1 1 1 II CH 2 CH 2 CH ch 2 CH, ch 2 1 1 1 1 ch 2 ch 2 ch 2 I CH, ch 3 1 1 1 CH, CH, CH, etc. etc. 1150] KREMERS — THE CLASSIFICATION OF CARBON COMPOUNDS 23 C n H2n CHj— CH 2 ch 2 — ch 2 CH 2 — CH 2 1 1 CH— CH 2 1 ch 3 ch 2 — ch 2 1 > CH ‘ ch 2 — ch 2 CH 2 — CH 2 1 1 CH— CH 2 ch 2 ch 2 — ch 2 1 1 1 CH 3 CH — CH 1 1 CH 3 CH 3 ch 2 — ch 2 ch 2 — ch 2 \ch, / \ CHi CRi CH — CH 2 \ / | ch 2 — ch 2 CH 3 A second dimethyl cyclobutane has been omitted for want of space. U51] 24 bulletin of the university OF WISCONSIN Whereas of the formula of saturation C 2n H 2n _i-2 but one series of hydrocarbons is possible, and representatives of but one series are known; of the formula of saturation C n H 2n , one chain series and an indefinite number of cyclic series can be developed. Repre- sentatives of the chain series and of four of the cyclic series are known. Derivatives of still another series with seven carbon atoms to the cycle are likewise known. The names of the normal chain hydrocarbons and initial mem- bers of the cyclic series are commonly given in accordance with the principles of the Geneva Congress. If we now proceed one step farther and abstract two more hydrogen atoms we arrive at the formula of saturation C n H 2n _ 2. Under this formula two unsaturated chain series and the following unsaturated monocyclic series and saturated dicyclic series may be developed. In the following tabulations some of the isomeric forms have been omitted for want of space on the page on which they be- longed. All isomeric forms with the double bonds in the side chains have been omitted for the same reason. These tables have been compiled, not with any idea of completeness, but rather for the purpose of affording a convenient oversight such as seems necessary for a proper grasp of the situation. [ 152 ] KRAMERS — THE CLASSIFICATION OF CARBON COMPOUNDS 25 CnH2n — 2 F F F CH III CH CH III C l 1 ch. CH ch 3 ch 2 III 1 II c 1 c III c CH 1 ch 2 CH 1 1 II CH, CH, ch 2 CH ch 3 ch 2 ch 2 III 1 II II c c CH CH 1 III 1 1 ch 2 1 c CH ch 2 1 II 1 ch 2 ch 2 CH CH 1 1 1 II ch 3 ch 3 ch 3 ch 2 CH ch 3 ch 3 ch 2 ch 2 ch 2 CH, III 1 1 II II 1 1 C c ch 2 CH CH CH CH 1 III 1 1 1 II II ch 2 1 c c 1 III ch 2 c CH II CH ch 2 1 ch 2 CH 1 1 ch 2 1 CH 1 ch 2 CH 1 1 1 II 1 II ch 2 ch 2 ch 2 ch 2 CH CH CH 1 1 1 1 1 II 1 ch 3 CHa CH 3 CH, ch 3 ch 2 CH, [ 153 ] 26 BULLETIN OF THE UNIVERSITY OF WISCONSIN CnH2n — 2 r a /CH ch 2 || \CH /CH ch 2 || \c /CH CH || \CH ch 3 ch 3 /CH /CH ch 3 /CH CH 2 || CH || 1 CH || \c 1 \CH /C 1 \c 1 ch 2 || 1 ch 2 ch 2 \c ch 3 ch 3 ch 3 | ch 3 1 ch 3 /CH /CH /CH /CH ch 3 CH, CH, ch 2 II CH 2 || CH || CH || 1 1 1 \c \c | \CH | \CH /C /C /C 1 1 1 1 CH 2 || CH || CH || ch 2 CH— CH 3 1 ch 2 CH— CH 3 \c |\CH Pi ch 2 ch 3 1 ch 2 | CH, ch 2 ch 2 j ch 3 ch, 1 CH, 1 CH, 1 CH, CH, [ 154 ] KRAMERS — THE CLASSIFICATION OF CARBON COMPOUNDS 27 CnH2n — 2 r a CHj— CH I II CH 2 — CH CH 2 — CH I II ch 2 — c I ch 3 CH 2 — CH I II CH— CH I CH, CH 2 — CH ! II CH 2 — c I ch 2 I CH* CH 2 — CH I II CH — CH I ch 2 I CH, CH, CH 2 — C I II CH 2 — c I CH, CH 2 — CH I II CH — C I I CH, CH, CH, I CH — CH I II CH 2 — c I CH, [ 155 ] 28 bulletin of the university OF WISCONSIN CnH2n — 2 r a ■ /CH 2 — ch CHj || \CH 2 — CH /CH 2 — CH /CH 2 — CH /CH 2 — CH CH 2 II CH 2 II CH II XCH*— C \CH— CH I \CH 2 — CH 1 1 1 CH 3 CH» CHj /CH 2 — CH 2 \ ch 2 ch 2 \CH = CH/ [ 156 ] kremers — the classification of carbon compounds 29 CnH2n — 2 A A CH 2 — CH /I CH — CH 2 CH 2 — CH I /I CH — CH CHg CH 2 — CH U-1 c — ch 2 ch 3 CH, CH, CH, CH 2 — CH CH 2 — CH | CH 2 — c | CH — CH | CH 2 — c 1 /I 1/1 1 /I 1 /! 1/1 CH — CH 1 c — ch 2 1 CH — CH 1 CH 2 — CH c — ch 2 ch 2 1 ch 2 CH, | CH, CH, 1 CHg 1 CH, [ 157 ] 30 bulletin of the university OF WISCONSIN CnH2n — 2 A A /CH— CHj CH 2 | | \CH— CH 2 /CH— CH 2 /CH— CH 2 /CH— CH 2 CH 2 | 1 CH,| 1 CHI 1 \CH— CH \C — CH 2 INCH— CH 2 1 1 1 CH, CH, CH, /CH— CH 2 \ CH 2 — CH— CH 2 ch 2 1 ch 2 I 1 \CH— CH 2 / CH 2 — CH— CH 2 [ 158 ] krkmers — the: classification of carbon compounds 31 It is not necessary to carry the details of this process any farther, if we but realize the important conclusion that can be derived from the few instances cited, viz., that the structural equivalent of two hydrogen atoms is either a double bond or a cycle, also that in place of two double bonds we may have still another structural equivalent, the treble bond. Bearing this in mind, we can readily classify under each formula of saturation the groups of series of hydrocarbons. In the follow- ing table these groups are indicated with the use of the following symbols : F — double bond A = cycle F — treble bond. C nH 2n + 2 c„h 2d ^n^2n_2 C n H 2n _ 4 r F F F F F A FA A A F F F A F A A AAA F F F A C n H 2D _ 6 r F F F F F F A F F A A r AAA AAA A C„H 2n _ 8 ^n ^2n — 10 ^2n — 12 7 F 6 r and 1 A 5 and 2 A etc. F F F F F F F A F A A Hence, the hydrocarbons may be rationally classified Firstly, According to their degree of saturation; Secondly, According to their chain or cyclic character; Thirdly, According to the number of carbon atoms. [ 159 ] 32 BULLETIN OB THE UNIVERSITY OF WISCONSIN CLASSIFICATION OF THE) SUBSTITUTION PRODUCTS OF THE HYDROCARBONS Having outlined very briefly, the principles that should govern us in a rational classification of the basal carbon compounds, the hydrocarbons, we are now prepared to classify their substi- tution products. In the large number of known hydrocarbons and in the thousands of unknown but possible hydrocarbons we have, in addition to carbon atoms that have their four affinities saturated exclusively with the affinities of other carbon atoms, the follow- ing three simple hydrocarbon groups: — CH 3> the univalent methyl group = CH 2 , the bivalent methylene group =CH, the trivalent methenyl or formyl group As has already been pointed out, methane constitutes the single exception to this rule. Hence its substitution products or derivatives differ somewhat from the analogous derivatives of other hydrocarbons. Inasmuch as we are going to regard all carbon compounds as substitution products, direct or indirect, of the underlying hy- drocarbons, all direct substitution must take place in connection with one of these three simple groups. This suggests at once one of the basal ideas of classification. Even more fundamental, however, is the conception of how often substitution has taken place. Inasmuch as it is the uni- valent hydrogen of the hydrocarbon that is replaced step by step, the unit of substitution must be a univalent atom or radicle. Accordingly we distinguish between mono-, di-, tri-, tetra-, etc., substitution products. This is done irrespective of the substitut- ing element or radicle. In order to illustrate the principles involved, substitutions with univalent elements also with the univalent hydride radicles of divalent and trivalent elements will be effected. [ 160 ] KREMERS — THE CLASSIFICATION OF CARBON COMPOUNDS 33 Halogen Substitution Products For substitution with a univalent element, the halogens are best adapted. Of mono-halogen substitution products there must be three types, since all three simple hydrocarbon groups contain at least the one hydrogen atom necessary for mono-substitution. — CH 3 — ch 2 x =CH 2 =CHX =CH =CX Whereas mono-substitution can take place only in connection with one carbon atom, di-substitution can take place in connec- tion with either one or two carbon atoms. If it takes place in connection with the same carbon atom, two types of di-substitu- tion products are possible, and only two, for but two of the three simple hydrocarbon groups contain the requisite two hydrogen atoms, viz. — CH 3 — chx 2 =CH 2 =CX 2 Tri-halogen substitution can take place in connection with one, two or three carbon atoms. If it takes place in connection with the same carbon atom, but one type of tri-halide is possible, since but one of the three simple hydrocarbon groups contains the requisite number of hydrogen atoms to admit of tri-substitution, viz. — CH 3 — CX 3 With the exception of methane, which, with its derivatives, as has already been pointed out, must occupy an exceptional posi- tion in any rational classification, tetra-substitution cannot take place in connection with one and the same carbon atom. Hence the possibilities of substitution in connection with one and the same carbon atom are exhausted with tri-substitution. Substi- tution in connection with different carbon atoms will be con- sidered later. Suffice it for the present to state that no new types are created by substitution in connection with different carbon atoms. The isomerism thus produced is one of position. [ 161 ] 34 bulletin op the university OP WISCONSIN The influence of position on the structure of a molecule is a study by itself and should not be confounded with that of simple types. Hydroxy Substitution Products Among the divalent elements of organic chemistry, oxygen is undoubtedly the most important. Inasmuch as the unit of sub- stitution in the underlying hydrocarbon is the univalent hydro- gen atom, it would not be rational to replace, step by step, hy- drogen atoms by their oxygen equivalents. Substitution, how- ever, can be rationally effected by a univalent oxygen-hydrogen radicle, such as we possess in the hydroxy or hydroxyl group, viz. the (— O— H). The simplest kind of hydroxy substitution product will na- turally be the mono hydroxide. As of mono-halides, and for the same reason, there are three types of mono-hydroxides or alco- hols. They are represented by the following type formulas: — CHj — CH 2 OH =CH 2 =CHOH =CH ~COH Of di-substitution products, in which the di-substitution has taken place in connection with the same carbon atom, two types of dihydroxides, or glycols, are possible, viz. — CH 3 — CH(OH ) 2 =CH 2 =C(OH ) 2 Of tri-hydroxides, in which all three hydroxy groups are con- nected with the same carbon atom, but one type is possible, viz. — CH S — C(OH ) 3 Such a tri-atomic alcohol in which all three hydroxy groups are connected with the same carbon atom is known as an ortho acid. It is a well known fact in organic chemistry that, whenever two or more hydroxy groups are connected with the same carbon atom, a tendency manifests itself to split off the elements of a molecule of water, a tendency readily interpreted with the aid of the thermochemical equation of water. [ 162 ] KREMERS — THE CLASSIFICATION OF CARBON COMPOUNDS 35 The two glycols, also the ortho acid, are subject to such de- hydration as indicated by the following type formulas: /H /H — C-OH — H 2 0= — C=0 \OH Aldehyde-yielding glycol /OH — C \OH Ketone-yielding glycol /OH ' — OH \OH — H 2 0= — h 2 o= Aldehyde =c=o Ketone /OH -C= Ortho acid Meta acid There are, therefore, as many as nine simple types of oxygen substitution products: six hydroxy substitution products, which, together with their dehydration products are herewith tabulated. Hydrocarbon Mono- groups hydroxides Dihydroxides Trihydroxides /H — ch 3 — c— h \OH Methyl Primary . alcohol /H =ch 2 =c— oh Methylene Secondary alcohol =CH =COH Methenyl Tertiary alcohol /H /OH — C— OH — C— OH \OH \OH .Aldehyde Ortho acid yielding glycol /H /O — c — c M) \OH Aldehyde Meta acid /OH =C \OH Ketone- yielding glycol =c=o Ketone [ 163 ] 36 BULLETIN OE THE UNIVERSITY OE WISCONSIN Amido Substitution Products Of the trivalent elements, nitrogen is unquestionably the most important in organic chemistry. However, it is not practicable to substitute, even in a theoretical way, one-third and two-thirds of a nitrogen atom for one and two hydrogen atoms, respectively. The simplest univalent nitrogen-hydrogen radicle, the amido or amino group, however, may replace the hydrogen of an under- lying hydrocarbon. As a matter of fact, it is with compounds such as these that the organic chemist has to deal. Hence the nitrogen derivatives can best be studied as amido substitution products and their deammoniated compounds. As with the halides and hydroxides, the monamides come first. Also, as with the mono-halides and mono-hydroxides, there are three types of monamides, according to the replacement of a methyl, methylene, or methenyl hydrogen atom, as indicated by means of the following formulas: — CH 3 — ch 2 nh 2 =CH 2 =CHNH =CH =CNH 2 In connection with the diamines we must again distinguish between those diamides in which the two amido groups are con- nected with the same carbon atom, and those in which they are connected with two carbon atoms. The former only are here considered. Of these there are again two types as of the cor- responding di-halides and di-hydroxides, viz. /H /H — C-H — C-NH 2 \H \NH 2 p/H _ r /NH 2 '~\H ~ l \NH 2 In like manner as the corresponding di-hydroxides readily split off the elements of a molecule of water, so the diamides, (though with less readiness) split off the elements of a molecule of ammonia, yielding the corresponding imides as indicated by the following formulas: /H /H — C-NH 2 — NH 3 = — C=NH \nh 2 = c 1 /H — C-OH \OH /H — c-nh 2 \nh 2 _ C /H So _ C / H C \NH _ C / R — C \H =c<£ _ C /° H —U \OH _ r /NH 2 “ L \NH 2 = C=0 =c=nh =CH [ 169 ] 42 bulletin of the university OF WISCONSIN Here again genetic relationship becomes apparent as expressed by such well-known reactions as the following: R'CHX 2 + 2M'OH = R'CHO + H 2 0 + 2M'X R' 2 CX 2 -f 2M'OH = R' 2 CO -f H 2 0 + 2M'X As is well known these reactions also are reversible: R'CHO 4- X 2 PX 3 = R'CHX 2 + OPX, R' 2 CO + X 2 PXa = R' 2 CX 2 + OPX 3 If in place of the imides, resulting upon deammoniation from the diamides, we substitute their hydroxy or oxy derivatives, the oximes, the genetic relationship between aldehydes and ketones, on the one hand, and their respective oximes, on the other hand, is readily expressed by the following general equations: R ' c