364 TRANSACTIONS OF SECTION B. 



distinct ways, each resulting in a configuration which contains an asymmetric 

 carbon atom. The bromine atoms may become attached at the same side of the 

 model as the methyl group or at the other side. In accordance with this predic- 

 tion it is found that the externally compensated, dextro-and laevo-1-methylcycZo- 

 hexylidene-4-acetic acids each yield two dibromides, which may be distinguished 

 as the a- and 0-isomerides. Those obtained from the active acids are them- 

 selves optically active, and on mixing them in equal quantities the externally 

 compensated dibromides obtained from the externally compensated acids are 

 produced. No evidence of any optical inversion was obtained from the study 

 of the bromination products. 



.The a- and 0- dibromides just referred to undergo two simple reactions which 

 reconvert them into compounds of the centroasymmetric type. On warming 

 with sodium carbonate solution they lose carbon dioxide and hydrogen bromide, 

 yielding l-methyl-4-bromomethylenecycfohexane (1), and when heated with 50 

 per cent, potash they lose hydrogen bromide alone, giving 1-methylcycZohexyli- 

 dene-4-bromoacetic acid (2), thus : — 



iH . >CH 2 ■ CHo\ yS. 



W X CH...CH./ x Br 



CH 3 . /CH 2 . CH.,\ 



>C( >CBr.CHBr.CO,H 



TT/ x f!W nil / 



H CH 2 .CH 2 CH .CH,.CH., V /CO.JB 



H/ \CH,.CH/ ^Br 



.. (2) 



Both these reactions proceed quantitatively, and when carried out with the 

 pure optically active a- or /3-dibromides, yield pure optically active centroasym- 

 metric products. 



The bromo-hydrocarbon and the bromo-acid (1) and (2) readily combine with 

 chlorine, yielding dichlorides which contain an asymmetric carbon atom in the 

 molecule. When these compounds are prepared from optically active materials 

 they are themselves optically active; each of course would be expected to con- 

 sist of a mixture of two isomerides related as are the o- and /3 dibromides. 



It is very noteworthy that the long series of changes to which the centro- 

 asymmetric optically active l-methylcycZohexylidene-4-aeetic acids have now 

 been subjected yield products which do, or do not, exhibit optical activity pre- 

 cisely in accordance with anticipations drawn from the study of the solid 

 models representing the configurations of the substances concerned. The convic- 

 tion that the structural formulae assigned to chemical substances imitate with 

 considerable approximation to truth the real nature of molecular constitution 

 was appreciably deepened by the introduction of the theory of the con- 

 figuration of methane derivatives by van't Hoff and Le Bel ; the development 

 of the theory by Wislicenus, so as to embrace the configuration of ethylene deri- 

 vatives, and by von Baeyer, in connection with polymethylene derivatives, has 

 strengthened the view that the constitutional formulas of organic chemistry 

 represent very closely the actual atomic arrangement of molecular complexes. 

 The considerations which led to the work described in the present paper involved, 

 as has been seen, the development of the original simple conception of the space 

 configuration of methyl and ethylene derivatives to an extent which may appear 

 extreme. The fact that we have been able to show a close correspondence be- 

 tween the anticipations thus derived and the experimental results must be 

 regarded as an independent demonstration of the fidelity with which constitu- 

 tional formula? depict molecular configuration. 



6. Report on the Study of Isomorphous Sulphonic Derivatives oj Benzene. 



See Keports, p. 82. 



