The relationship of structure to activity in plant-growth-regulating compounds. 2. Growth-regulating activity of substituted amides of 2,4-dichlorophenoxyacetic acid

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Abstract
The auxin activities of a number of N-substituted amides of 2,4-dichlorophenoxyacetic acid have been determined Wide variations in activity are shown by closely related amides. It is suggested that these amides are active auxins as such and do not of necessity require hydrolysis to the free acid within the plant before manifesting activity. The observed activities of these amides, taken in conjunction with their rates of hydrolysis in alkaline solution, can, with certain apparent exceptions, be related to the electronic status of the -C(O).N= portion of the molecules. The theory is advanced that an essential structural feature of an active auxin molecule is an electron-donating group or nucleophilic center at a particular position in the side chain of the molecule, and not, as previously believed, a carboxylic acid group. The low activity of apparent exceptions to this rule is explained as being due to competing donor groups which lead to misalignment of the molecule on the receptor centers in the plant.

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