Chemical configuration and action. Paste method 



addition to all the different salts and esters of the 2:4-dichlorophenoxy 

 acetic acid, the following substances were active as growth promoters: 

 2:4-dichlorophenoxyacetamide, 2:4-dichlorophenoxyacetic acid hydrazide, 

 2:4-dichlorophenoxyacetonitrile, and 2:4-dichlorophenoxymaleic acid 

 hydrazide. The group of 2:4:5-trichlorophenoxy derivatives which showed 

 promoting activity included 2:4:5-trichlorophenoxyacetamide, 2:4:5- 

 trichlorophenoxyacetic acid hydrazide, 2 :4:5-trichlorophenoxyacetonitrile, 

 2:4:5-trichlorophenoxyacetaldehyde, and sodium 2:4:5-trichlorophenoxy- 

 acetamidoethylsulphate showed slight activity. Many other substances 

 showed strong inhibiting activity, like indazole, 3-methylindazole, 1-methyl- 

 benzotriazole, 1-naphthoxyacetic acid, 4-oxycoumarin-3-butyric acid, salts 

 of the 3:6-endoxotetrahydro-o-phthalic acid, the zj^opropyl ester of carbamilic 

 acid, cinnamic aldehyde, 3:5-dinitro-2-methylbenzoic acid, 4:5-dinitro- 

 2-methylbenzoic acid, the lactone of the /j-oxy-/3-o-carboxyphenylpropionic 

 acid, aa-dichloropropionic acid, allyl cyanoacetate, sodium fiopropylxan- 

 thogenate, naphthoquinone, sodium 2:5-dichlorophenylacetate, sodium 

 2:4: 5-trichlorophenylacetate, ethyl 2:4: 5-trichlorothiophenoxyacetate, 

 pentachlorophenoxyacetic acid and its esters. A tetrachlorophenoxyacetic 

 acid product whose identity is not known exactly showed a small promoting 

 activity with a strong inhibiting component. 



It is of some interest, that 4:6-dichlororesorcin-bis(carboxymethyl) ether 

 and phenylimidodiacetic acid {Figure 6) were found to be practically inactive, 

 whereas bis-2:4-dichlorophenoxyacetic acid {Figure 7) proved to be a strong 

 inhibitor. This latter substance is of special interest, because it is somewhat 

 like a Siamese twin, the two 2:4-dichlorophenoxy rings being connected by 

 one acetic acid. In respect of the two-point attachment theory, the assump- 

 tion could be made that this substance must be active as promoter, because the 

 acid group is free as is an ortho position in one or both rings. No promoting 

 activity, however, nor any promoting component within the concentration- 

 action curve could be discovered; indeed, the curve we found was a purely 

 inhibiting one. The two-point attachment theory is here forced to make an 

 additional assumption: a steric hindrance. In other words, it must be 

 assumed that the steric form of other parts of the molecule are as much 

 involved in its activity as the 'two points' which are supposed to be necessary 

 for the growth-promoting action. In our view, it is more useful to consider 

 the form of the molecule in its entirety than only in terms of two separate 

 points. Nevertheless, I do consider it a good idea to nominate two distinct 

 points of the molecular structure as responsible for initiating the growth- 

 promoting action, provided that we assume that the association which takes 

 place between each of these points and the reacting living system occurs by 

 chemical reactions establishing real chemical bonds. But even in the case of 

 chlorinated phenoxyacetic acids, it is not obvious that the free 6-position will 

 give a true chemical reaction with another reacting group of the living 

 system. It therefore seems much better to assume that the 6-position is 

 involved in mode of action in a way other than by chemical reaction. 



The terminal group of the side-chain of a growth substance can be changed 

 within a wide range without losing activity. Thus we find the nitrile group 

 to be more active than the acid group, the latter, however, having a higher 

 activity than the aldehyde group. If we assume a chemical reaction to be 



V 145 



