| SECTIONAL TRANSACTIONS.—B. 359 
Friday, September 25. 
Discussion on The Chemistry of the Vitamins and Related Substances. 
(Introduced by Sir FrepERick GowLanp Hopkins, Pres. B.S.) 
Prof. P. Karrer.—The Chemical Constitution of Carotene and Related 
Substances. 
‘The carotinoids are a group of yellow pigments, which occur in plants as well as in 
animals. 
A considerable number of double linkages characterises their chemical constitution. 
; At present we know ten basic substances belonging to this group, and of these ten, 
two, Lycopine and Carotene, are hydrocarbons, having the composition C,)H;,. 
Two ways have proved particularly helpful in elucidating their constitution ; 
eatalytical hydrogenation, which gives the number of double linkages in the molecule, 
and degradation by oxidation, with ozone, potassium permanganate or chromic acid. 
Oxidation breaks up the large molecule, and from the fragments we gain an insight 
into the structure of the carbon chain. 
Lycopene C,,H;,, the pigment of the tomato, has thirteen double linkages, and is 
therefore an entirely aliphatic compound, with an open carbon chain. The results of 
the oxidation indicate for Lycopene a configuration most probably like formula I. 
Carotene occurs in two modifications, designated as «- and @- carotene. Of the 
two isomeric forms the «-modification shows a high degree of optical activity ; the 
f-carotene is optically inactive. The two modifications have a different melting 
oint and also differ in their absorption spectra. Both carotenes have eleven double 
ages and two carbon rings. The isomerism is brought about by a different arrange- 
ment of the double linkages. Formula II gives, with a high degree of probability, 
the constitution of the symmetrical optically inactive B-carotene. The assumption 
of this constitution is greatly strengthened by the results of the oxidation (6 mol. 
acetic acid and geronic acid). In the «-carotene it seems probable that one of the 
carbon rings has a configuration, as represented by formula III. It is possible to 
picture the two carotenes as having been derived from lycopene, bv the closing of 
two carbon rings, at the ends of the open chain. 
(a) The Chemistry of Vitamin A and the Carotinoids. 
ne ie CH; 
(CH;),C=CH.CH,CH,C=CH —-CH=CH—C=CH.CH=CH.C=CH.CH=CH.CH 
CH; CH; CH, 
| | 
=C—CH=CH—CH=C—CH=CH—CH=C.CH,CH,CH=C(CHs), 
3 Lycopene I. 
CH, CH, 
Pe CH, CH, 
| | 
CH, C—CH=CH—C=CH—CH=CH—C=CH-—CH Bitte CH, 
ae CH, CH, 
CH, C—CH, 
ar Be a ee oe Ramee CH, 
H,CC CH, 
: GH, 
@—Carotene II. 
