158 CAROTENOID HYDROCARBONS OF KNOWN CONSTITUTION X 



Further information can be found in the original communication^'^. Data 

 regarding vitamin A activity are given by Zechmeister and co-workers^'^. 

 Neo-a-carotene U possesses weaker growth-promoting properties than a-carotene. 



Neo-a-carotene W is formed together with neo-a-carotene U, as well as 

 several other stereoisomers not obtained in the crystalline state"^. Neo-a-caro- 

 tene W is found below neo-a-carotene U but above a-carotene in the chromato- 

 gram on calcium hydroxide and crystallises from a mixture of benzene and 

 methanol in small prisms, m.p. 97° (corr.). Its solubility is similar to that 

 of the U-isomer. 



Solvent: Absorption maxima: 



Carbon disulphide 502 469.5 m/< 



Benzene 484 453.5 ran 



Chloroform 484 453 m/x 



Petroleum ether (B.p. 60-70° C) . . . 470.5 441 m/z 



The absorption maxima of the crystalline and non-crystalline transformation 

 products in ligroin are shown below : 



Neo-a-carotene U (crystallised) . . . 471.5 441.5 m/i 



Neo-a-carotene V 465.5 437 m^ 



Neo-a-carotene W (crystallised) . . . 470.5 441 m/i 



Neo-a-carotene X 463.5 435 m/x 



Neo-a-carotene Y 467.5 437 vcifi 



a-Carotene (natural) 477 446.5 m^ 



Neo-a-carotene A 468.5 439 van 



Neo-a-carotene B 466.5 437 m^ 



Neo-a-carotene C 472.5 442.5 m/z 



Neo-a-carotene D 460 432 van 



Neo-a-carotene E 461.5 433.5 m/i 



(The sequence of isomers given is that in which they occur on the chromato- 

 gram). 



a-Carotene mono-epoxide and flavochrome C4oH5gO: 



CH3 CH, CH3 CH3 



/\ \ \ \ I /\ 



CH, C— CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-CH CHg 



)0 ' ' 



C CH2 

 CH, C • /\/ 



\/\ H3C CH 



CH2 CH3 a-Carotene mono-epoxide 



a-Carotene mono-epoxide is formed by the oxidation of a-carotene with 

 monoperphthalic acid (Karrer and Jucker^'*). It crystalHses from a mixture 

 of benzene and methanol in thin, reddish-yellow plates, m.p. 175° (uncorr., in 

 vacuum). On treating an ethereal solution of the pigment with concentrated 

 References p. i6§-iyo. 



