16 



VITAMINS A AND CAROTENES 



addition, a "m-peak" appears in the region of about 340 mju, the height of 

 which depends upon the number of cis isomers. These changes are illustrated 

 for a-, /S-, and 7-carotenes in Figs. 1, 2, and 3. Since the adsorption affinities 



I 

 o 



o e 



300 



400 



500 



Wavelength, m/z 



Fig. 1. Molecular extinction curves of a-carotene in hexane: , fresh solution 



of the all-Zmns form; , mixture of stereoisomers after refluxingin the dark for 



45 minutes; , mixture of stereoisomers after iodine catalysis in light at room 



temperature. [From /. Am. Chem. Soc. 65, 1522 (1943).] 



I 

 O 



u 



300 



400 



500 



Wavelength, m/i 



Fig. 2. Molecular extinction curves of /3-carotene in hexane: , fresh solution 



of the s\\-trans form; , mixture of stereoisomers after refluxing in the dark for 



45 minutes; , mixture of stereoisomers after iodine catalj'sis in light at room 



temperature. [From J. Am. Chem. Soc. 65, 1523 (1943).] 



