Relation of Halogen Position to Physiological Properties in the Mono-, Di-, and Trichlorophenoxyacetic Acids

The Role of Ortho-Substitution in the Synthetic Auxins

“…Some of the facts are consistent with another view, namely that a pair of para positions should be unsubstituted (8). However, neither of these views is completely satisfactory.…”

“…With the phenoxy acids, the data do not give a very clear-cut distinction between (a) the necessity of a free position ortho to the carboxyl (2, 3, 9, 10) and (b) the necessity of two free positions para to one another (8). The activity of the 2,6-acid and the real though small activity of the 2,4,6-substituted acids, contrasted with the inactivity of the 3,5-compound, however, favors the latter view.…”

On the Mechanism of Action of Growth Regulators

“…It seems likely that the growth inhibitor, maleic hydrazide, reacts in the same fashion as the lactones by reaction with a sulfhydryl group as follows: Undoubtedly a study of other stable organic compounds with double bonds activated by groups such as amides, esters, ketones, and nitriles would lead to the discovery of many compounds quite toxic to plant cells. Another recent study of the structure and activity of growth regulators is that of LEAPER and BISHOP (13). They have prepared and tested all of the possible mono-, di-, and trichlorophenoxyacetic acids.…”

“…These are (a) the effect of optical isomerism of the side chain (18,35,36), (b) the effect of geometrical isomerism of the side chain (31,32,33), (c) the ortho effect in benzoic acids (1,16), (d) the ortho effect in phenoxyacetic acids (7,13,17), (e) the inhibiting effects of lactones (6,32) and maleic hydrazide (4,9,14,40), (f) the inhibiting effect of cysteine (2), (g) the inhibiting effects of reagents specific for sulfhydryl groups (28,29), (h) the inactivity of phenoxyacetic acids without two open para positions (13), (i) the effect of electron-releasing and electron-attracting ring substituents (16). It is the purpose of this paper to present data on the relative activity of some growth regulators and to consider recent proposals for the reaction mechanism of the growth regulators in relation to the requirements listed above.…”

Effects of Growth-regulating Substances on the Carbon Dioxide Evolution and Post-harvest Ripening of Tomatoes.

“…The relative ineffectiveness of 2,4,6-T in inducing cell elongation and curvature, stimulating root formation, or bringing about toxic responses has been pointed out by several investigators (19,23,24,30,38,40). Mlore recently, however, Thimann (37) has shown that this compoundl shows auxin activity in the pea test.…”