Semiempirical quantum chemical methodology (AMI) has been employed to find out the potential energy (P.E.) surface for the acid-catalyzed condensation of ninhydrin with phenol. The AM1/RHF computed activation enthalpies (ΔH #) of the multi-steps chemical process show that the acid catalyzed arylation of ninhydrin should take place smoothly at room temperature, very much consistent with the experimental results. NMR and crystallographic studies show that the monoarylated ninhydrin adducts from phenols preferably remain in intramolecular hemiketal form. AM1/RHF computed heats of formation in some representative cases also favour such intramolecular hemiketal formation.