AM1 study on the conformations of keto-enol tautomerism in methicillin

Abstract

The geometry, conformation and electronic structure of keto-enol tautomerism in methicillin have been optimized and calculated in the gas phase usually considering an isolated molecule surrounded by vacuum using semi-empirical molecular orbital AM1 method. The mechanism of protonation in enol tautomer of methicillin has been studied by comparison of the different positions of net charges at nitrogen atoms in the molecule. Further, the heats of formation (∆H_f^o), dipole moment (µ), ionization potential (IP), full atomic charges and energies of frontier molecular orbitals (E_HOMO and E_LUMO) have been performed and discussed. The conformational analyses of mono- and di-protonated enol tautomers have also been performed for their stable conformations.