TRANSACTIONS OF SECTION B. 363 



The configuration of l-methyl<y(.7ohexylidene-4-acetic acid may be repre- 

 sented in the following maimer : — 



9 



(&) CH 3 ., ,CH . CEU M ic) 



(a) H''iVh,CH/4 7 N C0 2 H (rf) 



in which those bonds represented by unbroken lines all lie in one plane, and 

 those represented by broken lines lie in a plane perpendicular to the first ; if the 

 continuous lines represent bonds which lie in the horizontal plane of the paper, 

 the broken lines stand for bonds which lie in the vertical plane passing through 

 the carbon atoms numbered 1, 4, and 7. It will now be seen that the plane of 

 the paper which contains the continuous line bonds is not a plane of symmetry 

 of the solid configuration, because the hydrogen atom marked (a), which lies 

 outside that plane, is not repeated on the other side of the plane, the sym- 

 metrical position being occupied by the methyl group (b). Similarly the vertical 

 plane remarked above is not a plane of symmetry of the configuration, because 

 the groups (c) and (d), of different compositions, occupy symmetrical posi- 

 tions on the two sides of the plane. In the same way it can be shown that no 

 other plane is a plane of symmetry of the configuration as above represented. 

 Further, no directions can be distinguished as axes of symmetry of the solid 

 configuration, nor can any point be located within it as a centre of symmetry. 

 It is thus seen that when a highly symmetrical configuration is attributed to 

 methane derivatives the configuration assignable to l-methylci/cfohexylidene-4- 

 acetic acid possesses neither planes, axes, nor a centre of symmetry. The absence 

 of all these elements of symmetry is more than is requisite to determine the 

 enantiomorphism of the configuration. 



In order to distinguish substances of enantiomorphous molecular configura- 

 tion which contain no asymmetric atom in the molecule from those in which an 

 asymmetric atom is present, it is convenient to describe the former as ' centro- 

 asymmetric.' The discovery of optically active centroasymmetric compounds 

 opens up a wide field of stereochemical inquiry, part of which we have recently 

 explored. 



Thus, the centroasymmetric l-methylcycZohexylidene-4-acetic acids can be con- 

 verted into the 1 -methyl- A 3 -ci/cfohexene-4-acetic acid of Marckwald and Meth, 

 in which an asymmetric carbon atom is present ; it became important to perform 

 this conversion upon optically active material in order to ascertain whether optical 

 inversion attends the change. On heating laevo-l-methylcycZohexylidene-4-acetic 

 acid with water, sulphuric acid and alcohol, the required conversion takes place, 

 but the product, the acid of Marckwald and Meth, is optically inactive. It 

 is concluded that the change occurs with formation of a saturated hydroxy- 

 acid as an intermediate product, in accordance with the following scheme : — 



CH 1V ,CH. 2 .CH 2 . CH 3V /CH„.CH... 



>C\ >C:C.CH.CO.,H^ >C< >C(OH) .CH... CO.H 



W \CH,.CH/ W X CH,.CH./ 



(1) Optically active. (2) Potentially inactive. 



-» yK ' >C.CH,.CO..H 



H x N CIL.CH./ 



(3) Externally compensated. 



More importance attaches to the addition of bromine to the unsaturated centro- 

 asymmetric acid, a reaction which results in the formation of a saturated acid of 

 the constitution, 



\r/ " ^CBr . CHBr . CO..H. 



S CH 2 .CH/ 





The inspection of a stereochemical model of the molecular configuration of the 

 saturated acid shows that the two atoms of bromine may be taken up in two 



