RHF CONFORMATIONAL-ANALYSIS OF THE AUXIN PHYTOHORMONES N-ETHYL-INDOLE-3-ACETIC ACID (N = 4, 5, 6)

RHF/G-31G investigations of 4-, 5-, and 6-ethyl(Et)-indole-3-acetic a cid (IAA) yielded 11 symmetry-unique local minima with syn-periplanar orientation of the -COOH group for each of these compounds. The global minima are of C-1 symmetry in all cases. Comparison with earlier resu lts shows that ethylation or chlorination in position 5 or 6 introduce s only minor changes on the orientation of the acetic acid side group, with no effect on the reaction paths related to this group. For 4-Et- IAA, the deviations from unsubstituted IAA are larger but preserve the pattern of reaction paths that is present in unsubstituted IAA,which is in contrast to 4-Cl-IAA, where local minima and reaction paths are completely different. (C) 1998 John Wiley & Sons, Inc.