thank you rafik sir,

i am thinking to write a concerted reaction for methyl guaiacol decomposition to form a guaiacol. How to form a TS structure for this reaction?

Two options - first, if you have some idea what the TS might look like, then build that structure, use opt=ts in G09, and let it go - second, if you have no sensible idea, then you can enter a structure for the reactant, a structure for the product and use opt=qst2 to find the TS in G09 -