Przibytek tried in vain to divide. In fact, such a compound was to be predicted from the formula : CO2H HCOH CO2H Erythrite, CH,OH (CHOH),CH,OH, may be cited as a second instance of this inactive indivisible type, since Przibytek 2 has shown that this yields on oxidation the inactive non-racemic tartaric acid. From the constitution of erythrite the possibility of inactivity without divisibility was, in fact, to be expected. Thirdly, we must now add erythrene- or pyrrolylenebromide, CH,Br(CHBr),CH,Br (tetrabromobutane), since Griner has converted this into erythrite; the liquid isomeric bromine compound would then represent the racemic mixture. 4 Here, too, we must mention several compounds whose constitution resembles that of tartaric acid in that they possess a symmetrical formula with two asymmetric carbon atoms. These compounds possess a special interest because they all present a case of isomerism, which, inexplicable according to the old views, is a self-evident necessity of our theory. As in the case of erythrenetetrabromide, these isomers correspond to the inactive indivisible tartaric acid and to racemic acid. Most of these compounds 4 Henninger, Compt. Rend. 104, 144; Ciamician, Ber. 19, 569; 20, 3061; 21, 1430. have been investigated by Bischoff in his study of the bisubstituted succinic acids possessing the symmetrical formula, CO,H(CHX),CO,H. Such are the dibromo- and isodibromo-succinic acids, dimethyl-,' diethyl-,2 diisopropyl-,3 and diphenyl-succinic acids, with their derivatives, ethers, anhydrides, &c., which also form isomers. Recent additions to the list are the dimethyldioxyadipic acids,5 (CO2H.CH2.C.OH.CH2)2, and the thiodilactylic acids (CO2H.CH,.CH),S. 6 Although up to the present none of these isomers has been divided, yet there is such an intimate connection between their formulæ and those of the tartaric acids that it is difficult to doubt of ultimate success. We have only to substitute methyl, &c., for the hydroxyl of the tartaric acids, and it is more than probable that the isomeric relations of these. acids will survive the substitution. 7 To this class belong also hydro- and isohydrobenzoïn, CH, (CHOH),C,H,, with some derivatives and homologues. These are comparable with tartaric acid, the carboxyl group being now replaced. Finally, we must mention the bromides of nitrostilbene, NO,C,H(CHBr),C,H,NO,, and also bi- and isobi-desyl, CH,(CHCOC ̧H2),CH ̧.9 5 6 6 8 9 1 Ber. 18, 846, 2368; 20, 2736; 21, 3170; 22, 66, 1821. 2 Bischoff and Hjelt, Ber. 20, 2988, 3078; 21, 2089; 22, 67; 23, 650. 3 Hell and Mayer, Ber. 22, 56. + Reimer, Ber. 14, 1802; 15, 2628; Ossipoff, Compt. Rend. 109, 223; Tillmanns, Ann. 258, 87; 259, 61. 5 Zelinsky and Isajew, Ber. 29, 819. 7 Auwers, Ber. 24, 1778. 6 Loven, l.c. 1132. Bischoff, Ber. 21, 2074. 9 Knövenagel, Ber. 21, 1359; Garett, 21, 3107; Fehrlin, 22, 553. If symmetry exists the two isomers marked No. 1 become identical and inactive; the same with No. 8; the pair No. 2 coincides with No. 5, and No. 3 with No. 4. Hence we have ten isomers, of which two are inactive and indivisible, while the other eight belong to four types. Now, in the case of mannite, CH2OH (CHOH),CH,OH, we have : = Left and right (ordinary) mannite,' [a], +0.03; with boric acid, more strongly right-handed. Left and right (ordinary) sorbite,2 slightly active; with borax, [a]=1·4. Dulcite, inactive, indivisible.3 In the case of the corresponding saccharic acids, indeed, all the six types exist : Left and right (ordinary) saccharic acid, [a],=8°; as lactone, 38°.4 Left and right mannosaccharic acid, slightly active; as double lactone, 202°.5 Talomucic acid," [a],> +24°; as lactone, <+7°. Kiliani, Ber. 20, 2714. 3 Ber. 25, 2564, 1247. 5 Ber. 24, 541, 3628. 7 Fischer, l.c. 25, 1247. 2 Fischer and Stahel, Ber. 26, 2144. 4 Tollens's Kohlehydrate. 6 Fischer, Ber. 24, 3622. 8 Fischer, l.c. 24, 2136 CHAPTER IV DETERMINATION OF THE POSITION OF THE RADICALS IN STEREOMERS WHEN the number of the isomers actually existing (which, in the cases we have been considering, may be called stereomers) agrees with the theory, we are confronted with a problem like that which we have to solve in the aromatic series, when we assign to each of three derivatives one of the three symbols 1, 2, 1, 3, 1, 4. At present this problem can be solved only partially which of the two enantiomorphous formulæ corresponds to, say, the left-rotating compound, is undecided. When, however, there are several carbon atoms the case is different. We have already mentioned such types. In the case of tartaric acid, e.g. (p. 75), the symbol CO2H HCOH нсон was chosen on account of its symmetry as the expression for the 'inactive indivisible type,' while the two other formulæ remained for the right- and leftacids; to decide between these last is, however, G impossible. It is especially in the sugar group that the determination of configuration, in this sense, has been carried out by Fischer.' In now discussing the special data and results, since we can choose the formula for the type only, and not for the right- or left-handed product in question, we find that the number of symbols to be distributed is reduced by half, which greatly simplifies the discussion. In what follows, therefore, the mirror-images, such as represent the same tartaric acid-in this case the active one. In order now to facilitate the review of the sugarderivatives we will take in succession first the simplest, the tetroses, COH(CHOH),CH2OH, then the pentoses, COH(CHOH),CH,OH, and finally the glucoses, COH (CH.OH),CH,OH. Then we have 4, 8, and 16 isomers, or 2, 4, and 8 types, and the first two are directly connected with the tartaric acids, their symbols being and the substances represented by the first symbol giving inactive, indivisible tartaric acid, those represented by the other giving the left or right Ber. 24, 1836, 2684. |