498 



SCIENCE 



[N. S. Vol. XLVI. No. 1195 



A — ; and an atom whose valence is n may 

 function in (71-+ 1) ways electronically. 

 Thus: 



O 



+ 



o 



+ , oz. 



+ + + — 



N + , N + , N — , N — . 



A compound formed by the union of the 

 univalent atoms, A and B, may be repre- 

 sented by two electronic formulas: 

 A -1 B and A — + B. 



These two formulas represent isomers in a 

 peculiar sense, quite unlike structural 

 isomers. The difference lies solely in the 

 distribution of valence electrons. Two or 

 more compounds related in this manner 

 have been called electronic isomers, or 

 electromers.^^ 



There is a certain resemblance between 

 electromers and structure tautomers. 

 "While the transformation of one tautomer 

 into another is accompanied by a wander- 

 ing of an atom from one position in the 

 molecule to a new position, the transforma- 

 tion of one electromer into another depends 

 upon a more subtle change, viz., of elec- 

 trons, or negative atoms of electricity, from 

 one position to another within the mole- 

 cule. Furthermore, it would be expected 

 that, like tautomers, one electromer would 

 be more stable than the other, and, in the 

 majority of cases, that only one form 

 might be capable of isolation, but that 

 under certain favorable conditions, both 

 electromers might be realized. 



Moreover, between two electromers there 

 might exist a condition of equilibrium simi- 

 lar to that which exists between tautomers 

 and desmotrops, viz., 



A + — B-^A \-B. 



Many cases requiring an assumption of 

 such a relationship have been observed. 

 One simple illustration will suffice. When 

 IS Fry, Z. Physih Chem., 76, 387 (1911). 



benzene sulphonic acid is subjected to the 

 action of superheated steam, it yields ben- 

 zene, CeHg, and sulphuric acid. But if the 

 same sample is heated with caustic alkalies, 

 the products are phenol, CeHuOH, and 

 sulphurous acid (or sulphites). Since ben- 

 zene and phenole, as well as sulphurous 

 acid and sulphuric acid, are related as oxi- 

 dation-reduction products, the question 

 arises what is the electronic formula of ben- 

 zene sulphonic acid? To account for the 

 substances formed in the two reactions, it 

 must be assumed that two electronic for- 

 mulas may be assigned to benzene sul- 

 phonic acid, and that the two substances 

 represented by these formulas are in equi- 

 librium as tautomeric electromers^''' 

 C„H„ h SO3H ^ C,Hj -I- — SO3H. 



It is self-evident that the problem of 

 preparing two or more electromers presents 

 far greater experimental difficulties than 

 the separation of structure tautomers has 

 offered in the past. When, therefore, it is 

 recalled that von Baeyer observed the first 

 case of tautomerism while studying isatin, 

 and that many years elapsed before two 

 compounds related as tautomers were ac- 

 tually separated as distinct substances 

 (desmotrops), it should not be a matter of 

 surprise that the preparation of actual 

 electromers has not been more successful 

 so far. 



The first set of experiments, and prac- 

 tically the only ones, carried out with the 

 express purpose of preparing electromers, 

 are those of W. A. Noyes.'^ Noyes tried to 

 prepare a nitrogen trichloride in which the 

 chlorine atoms, like those in phosphorus tri- 

 chloride, are negative 



-H — Cl 



NH CI 



-^ — CI. 



No conclusive evidence in support of the 

 14 L. W. Jones, Am. Chem. J., 48, 26 (1912). 

 iB"W. A. Noyes, J. Am. Chem. Soc, 35, 767 



(1912). 



