engleski

RHF conformational analysis of the auxin phytohormones n-ethyl-indole-3-acetic acid (n=4, 5, 6).

Each of the potential energy surfaces of 4-, 5-, and 6-ethylindole-3-acetic acid (Et-IAA) contains four symmetry unique energy minima. The global minima are always characterized by an out-of-plane orientation of the ethyl group. The acetic acide side chain, however, is coplanar with the indole nucleus in 5- and 6-Et-IAA, whereas it is tilted in 4-Et-IAA. In the latter case, the two side chains point towards opposite sides of the indole nucleus ; as a consequence of this conformation, a weak hydrogen bond C-H&middot ; &middot ; &middot ; O=C is formed between the methylene group of the ethyl side chain and the carbonyl oxygen atom, with a hydrogen bond distance of 2.552 &Aring ; and a bond order of 0.021. Comparison with the results obtained earlier for unsubstituted IAA shows that ethylation in position 5 or 6 introduces only minor changes of the PES. Also, the reaction paths related to the acetic acid side chain are basically identical. The same has been found for 5- and 6-Cl-IAA. In the case of 4-Et-IAA, the deviations from unsubstituted IAA are much larger. Interestingly, the qualitative picture, which emerges from the PES of 4-Cl-IAA, IAA, and 4-Et-IAA, is well in accord with the measured biological data

Ab inito; conformational search; n-ethyl-indole-3-acetic acid

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