Ideas of Quantum Chemistry P86 shows how quantum mechanics is applied to chemistry to give it a theoretical foundation. The structure of the book (a TREE-form) emphasizes the logical relationships between various topics, facts and methods. It shows the reader which parts of the text are needed for understanding specific aspects of the subject matter. Interspersed throughout the text are short biographies of key scientists and their contributions to the development of the field. | 816 14. Intermolecular Motion of Electrons and Nuclei Chemical Reactions The starting point R has occupation n 2 x 2 and that is fine because we are dealing with the DA structure. The intermediate stage represents a mixture of two structures mainly with almost equal contributions n 2 x 2 . DA and n 1 x 2 x 1 . D A-. Therefore we may expect that the population of x is close to 2 of n is about while of x is about . This is indeed the case. The final stage P is a mixture of the D A- structure which corresponds to the occupation n 1 x 2 x 1 of the structure D A- corresponding to n 1 x 1 x 2 and the structure D 2A-2 with occupation n 0 x 2 x 2. Equal contributions of these structures should therefore give the occupations of n x x equal to j and respectively. The population analysis gives similar numbers see Table last column. NUCLEOPHILIC ATTACK H- ETHYLENE ETHYLENE H- Maybe the acceptor-donor theory described above pertains only to the H- H-H reaction Fortunately enough its applicability goes far beyond. Let us consider a nucleophilic attack of the H- ion on the ethylene molecule Fig. perpendicular to the ethylene plane towards the position of one of the carbon atoms. The arriving ion binds to the carbon atom forming the CH bond while another proton with two electrons . H- ion leaves the system. Such a reaction looks like it is of academic interest only except some isotopic molecules are involved . when one of the protons is replaced by a deuteron but comprehension comes from the simplest examples possible when the least number of things change. The LCAO MO calculations for the ethylene molecule give the following result. The HOMO orbital is of the n bonding character while the LUMO represents the antibonding n orbital both are linear combinations of mainly carbon 2pz atomic orbitals z being the axis perpendicular to the ethylene plane . On the energy scale the H- 1s orbital goes between the n and n energies similarly as happened .
