— 165 — 



the presence or absence of conjugated double bonds of any variety be 

 determined by molecular refraction or dispersion? In order to obtain a 

 better basis for comparing the ascertained values, the authors founded 

 their data upon the centuple value of the specific refraction, for which 

 they propose the signs ^ a , - D , $c. This value is obtained by multiplying 



the mol. refr. by the fraction — : t-tt' If the values found by pre- 



J mol. weight J 



vious authors are converted into 2 it will be found that altogether only 

 two groups of combinations with abnormally high mol. refr. are known 

 which do not possess conjugated double bonds, that is to say, Wallach's 

 menthene derivatives with semi-cyclic double bond and the derivatives of 

 the carbon tricyclic ring. A conjugated double linkage does not always 

 cause exaltation, very commonly the addition of side-chains to the central 

 carbon-atoms lowers the optical activity and may counterbalance a possible 

 an eventual exaltation. Such systems the authors call "disturbed con- 

 jugations", and they distinguish between "undisturbed", "once disturbed" 

 and "repeatedly disturbed" conjugations. The addition of substitutes to 

 the carbon atoms in end-position of a conjugation likewise diminishes 

 generally the optical activity of the latter, but the action is very unequal 

 ("lateral disturbances"). When both central and lateral disturbances occur, 

 their effect is particularly pronounced. By this method the optically normal 

 behaviour of phellandrene is accounted for by the fact that it has a "disturbed 

 conjugation". 



If the substituent causing the disturbance itself contains a double 

 bond (so-called "crossed" double bonds) this fact is indicated by an 

 abnormally pronounced disturbance, whereas three following double bonds 

 produce avery high exaltation. Where the occurrence of semicyclic 

 double bonds and of tricyclic rings is excluded, the existence of exaltation 

 warrants the cer tain conclusion that conjugated double bonds are present. 

 Compounds which contain no conjugation, nor a semicyclic double 

 linking, nor a tricyclic ring, present no optical anomalies. Judged by this 

 theory the formula given by Fisher and Perkin 1 ) for the isocarvestrene 

 prepared by them, viz: — 



CH 



H 2 C 

 H 2 C 



CCH 8 

 CH 2 



CH 

 H3 C • C : CH 2 



cannot be correct, and will probably have to be replaced by the following: 



*) Journ. chem. Soc. 93 (1908), 1876; Report April 1909, 123. 



