NBO analysis has been made for the understanding of hyperconjugative interactions. QTAIM analysis is performed to determine hydrogen bonding. Molecular electrostatic potential mapping and Global reactivity descriptors were used to explain the chemical reactivity. FT-IR and FT-Raman spectra of ampicillin were compared with the theoretical result. Spectra are simulated by DFT for monomer, dimer and tetramer of ampicillin using optimized geometry.