STRUCTURE OF THE VITAMINS A (593 



Several possible formulas have been suggested. The first proposed struc- 

 ture was that of Gillam et al.^^ which differs from that of vitamin Ai in 

 having an extra vinylene group on the aliphatic chain, and therefore pos- 

 sesses a C22 composition. 



HjC CHj 



\ / 



c 



/ \ H H 



HzC c • c : c • c : c • c : c • C : C • C : c • CHjOH 



I II 

 H2C c 



\ / \ 



C CHj 



Hi 



Formula I for vitamin A2 proposed 

 by Gillam et alJ^ 



A second suggested formula for vitamin A2 is that of Karrer, Geiger, 

 and Bretscher,^*^ which contains an open jS-ionone ring and bears the same 

 relation to vitamin Ai as lycopene does to |3-carotene. Morton, Salah, and 

 Stubbs^^' have proposed a third formula for vitamin A2 which contains a 

 dehydroionone ring. 



HjC CHj 



r CHj CHj 



/\ hhIhhhIh 

 HzC c«c:C' c.'C'C: c- c: c* cHjOh 



I 11 



HC C 



^ / \ 

 C CHj 



H 



Formula III for vitamin A2 proposed 

 by Morton et aZ.^'' 



The strongest evidence for the Gillam formula (Formula I) is that, on 

 oxidation of vitamin A2 with aluminum ier^-butoxide in the presence of ace- 

 tone, as described by Batty et al.^^* for vitamin Ai, a ketone is produced 

 with an empirical composition of C25H34O as deteiTnined from the crystal- 

 line p-chlorobenzo3^1hydrazone derivative (m.p., 142-143°C.).'^ Vitamin 



'32 P. Karrer, A. Geiger, and E. Bretscher, Helv. Chim. Acta, 2^, 161E-172E (1941). 

 1" R. A. Morton, M. K. Salah, and A. L. Stubbs, Nature, 159, 744 (1947). 

 '3^ J. W. Batty, A. Burawoy, S. H. Harper, I. M. Heilbron, and W. E. Jones, J. Chem. 

 Soc, 19S8, 175-179. 



