ABSTRACT
In this chapter, Hückel has put forward some pertinent points of assumption for writing thesecular equations and secular determinants for conjugated systems and cyclic polyenes. This chapter consists of applications of the Hückel molecular orbital (HMO) method to π system, such as ethene, its total π energy and delocatisation energy, HMO coefficients and MO of ethene, and the energy levels of ethene. It also gives HMO treatment to allyl system, butadiene and their secular equations, secular determinants their solution, their roots, their HMO coefficients, their energy levels (bonding and antibonding levels), total π electron energy, their delocalisation energies, bond orders, electron density, and free valence. It also provides application of the
Hückel method to some cyclic polyenes, such as cyclopropenyl, cyclobutadiene, and cyclopentadienyl system, benzene, and their HMO treatment as above, and to find out the electron density, bond order, free valence, delocalisation energy, energy levels, HMO coefficients, and MOs. The chapter also discusses the generalised treatment of HMO theory to open-chain conjugated systems and cyclic polyenes. It also comprises extended Hückel theory; hetero atom substitutions; and applications to pyrrole, pyridine, and naphthalene. The HMO treatment will remain the same for these substances. At the end of the chapter, it consists of references, solved problems, and questions on concepts.
