On form and function of plant growth substances 



It is well known that o-substituents larger than CH3 or CI, though no 

 doubt causing the COOH group to occur in the active spatial position, do 

 not confer activity to benzoic acids. This is caused very probably by masking 

 of the COOH group, thus excluding it from the interaction with its counter- 

 part in the cell. 



Figure 1. Mult I alt inudcL\ uj — O 



Left : Benzoic acid. The molecule tends to take a flat form, as structures like + / \=C\ 



^— \+ /O" \=X \oH 



and <( ^=C\ contribute to the mean state. 



\^=/ \OH 



Right: 2:6-Dichlorobenzoic acid. Non-flat form, the o-substituents causing steric inhibition of 

 resonance. 



As to the 3-position, apparently more latitude is left, as we found 3-cyano- 

 methyl-2:6-dimethylbenzoic acid (I) to be active {Figure 2). 



COOH COOH COOH 



H3C- 



— CH, 



— CH2CN 



I 



COOH 



CH 



IV 



.CH. 



-CI ^'^' 



H3C- 



COOH 



-CH2CH3 



—CI 

 II 

 COOH 



-CHn 



CH, 



V 



H3C- 



H3C- 



-I 



—CI 

 III 

 COOH 



-CH3 

 -CH, 



COOH 



VI 



CI— i 



I 



F 



-CI 

 -CI 



VII 



Cl- 



-Cl 

 -NO, 



VIII 



119 



