COMPARATIVE AB-INITIO SCF CONFORMATIONAL STUDY OF 4-CHLORO-INDOLE-3-ACETIC ACID AND INDOLE-3-ACETIC-ACID PHYTOHORMONES (AUXINS)

An ab initio conformational analysis of 4-chloroindole-3-acetic acid w as performed at the RHF/6-311G* level. The mirror symmetrical conform er (in which the indole ring is coplanar with the COOH group) is most stable; next in energy are the two conformers with the C-COOH fragment perpendicular to the indole ring with relative energies of 2.72 and 6 .69 kJ/mol. H ... Cl hydrogen bonding results in only a minor stabiliz ation. The results are combined with those obtained earlier for indole -3-acetic acid and recent biological data regarding auxin (growth horm one) activity. From this, assumptions concerning the biologically acti ve conformation are drawn. (C) 1996 John Wiley & Sons, Inc.