The potential energy surface (PES) of 2-methylindole-3-acetic acid (2-Me-IAA) has been investigated via RHF/6-31G* and RHF/6-31++G** calculations. With both basis sets, only three symmetry unique local minima with syn orientation of the COOH group are contained in the PES. A network of reaction paths connects these energy minima. One symmetry unique energy minimum has an extremely low barrier to the adjacent global minimum. Comparison with unsubstituted IAA and its alkylated as well as halogenated derivatives substituted at positions 4, 5, 6, and 7 shows that the PES of 2-Me-IAA is quite different. This is in accord with its significantly lower auxin activity and weaker binding to auxin binding protein 1 (ABP1)
