The calculation of molecular orbitals provides information about the electronic structure and chemical properties of a molecule by describing the spatial distribution and energies of electrons within the molecule. Molecular orbitals are formed from the linear combination of atomic orbitals LCAO of the atoms involved in the molecule. These molecular orbitals can be bonding, non-bonding, or anti-bonding, depending on the overlap and phase of the atomic orbitals.The electronic structure of a molecule can be determined by populating the molecular orbitals with electrons according to the Aufbau principle, which states that electrons fill the lowest energy orbitals first. The resulting electronic configuration provides insight into the molecule's stability, bond order, and bond strength.Chemical properties and reactivity of a molecule can be predicted by analyzing the molecular orbitals, particularly the highest occupied molecular orbital HOMO and the lowest unoccupied molecular orbital LUMO . The HOMO represents the electrons that are most likely to be involved in a chemical reaction, while the LUMO represents the available orbitals for electrons to be added during a reaction.The energy difference between the HOMO and LUMO, known as the HOMO-LUMO gap, is an important factor in determining the reactivity of a molecule. A smaller HOMO-LUMO gap indicates that the molecule is more reactive, as it requires less energy for an electron to be transferred from the HOMO to the LUMO during a reaction. Conversely, a larger HOMO-LUMO gap indicates a more stable and less reactive molecule.Molecular orbital calculations can also provide information about the electron density distribution in a molecule, which can be used to predict the sites of nucleophilic and electrophilic attack in chemical reactions. Regions of high electron density are more likely to be nucleophilic, while regions of low electron density are more likely to be electrophilic.In summary, the calculation of molecular orbitals provides valuable information about the electronic structure, stability, and chemical properties of a molecule. This information can be used to predict the reactivity of the molecule in chemical reactions, as well as the likely sites of nucleophilic and electrophilic attack. By understanding these factors, chemists can design and predict the outcomes of chemical reactions, develop new synthetic routes, and create novel molecules with desired properties.