108 PHYTOHORMONES 



formulae of these two closely related compounds has been 

 elucidated, although the whole amount of active crystals 

 available was only 700 mg. (Kogl, Erxleben, and Haagen 

 Smit, 1933; Kogl and Erxleben, 1934, 1935). 



First the acid and lactone were shown to have but one 

 double bond, and the acid to have one COOH group. After 

 addition of hydrogen at the double bond, the number of 

 H atoms in the molecule is still two short of saturation, and 

 hence there must be one ring in the molecule. In auxin a the 

 remaining three oxygen atoms were found to be in hydroxyl 

 groups, while in auxin h one hydroxyl and one keto-group 

 could be identified. Oxidative degradation of both auxin 

 a and h gave rise to a C 13 dicarboxylic acid which contained 

 no hydroxyl groups. Similar oxidation of the hydrogenated 

 derivative, which is biologically inactive, yielded a neutral 

 Ci3 ketone. The oxidation has therefore carried away all the 

 hydroxyl groups, together with a chain of 5 C atoms. From 

 the difference between the two oxidations it is also clear 

 that the double bond was not in the side chain which was 

 removed. Further reasoning indicated that this side chain 

 contained the three hydroxyl groups and the COOH group, 

 and established their relative positions; hence the oxidations 

 must be formulated as follows, substance I being auxin a, 

 and II dihydro-auxin a: 



/C.CHOH.CHo.CHOH.CHOH.COOH /COOH 



^CH I ^COOH III 



.CH.CHOH.CH2.CHOH.CHOH.COOH /CO 



\CH2 ;i ^CH2 IV 



/C.CHOH.CH2.COCH2.COOH. 



\CH V 



Since auxin h loses CO2 on heating to give a neutral ketone, 

 it must have its keto-group in the /3-position and therefore 

 be formulated as V. The relation between these two com- 

 pounds, auxin a and h, or auxentriolic and auxenolonic 



