The Application Of Symmetry In Structure Chemistry

In order to make theoritical and practical preparations for editing a new textbook of structural chemistry, this thesis mainly sums some symmetry theories in structural chemistry, compares different calculation approaches, presents some views on disputable questions concerning symmetry and some shortcomings in the in-effect textbooks ,and links main contents of structural chemistry on the base of symmetry principles. Firstly, as the thesis elucidates, the symmetry of a system results in conservation of its corresponding mechanical parameters. If two mechanical parameters of a system commute with each other, it is reasonable to use corresponding quatum numbers to symbolize the eigen state of the system. For example ,for 1L.LZ and S~ of one-electron atom system are commuting ,then, n ,l,m and m5 can be used to sign its eigen state. If H of a molecular system also commutate with symmetry operator of its point group, then - irreducihle representations can mark canonical molecular orbitals. Therefore, symmetry is the base of the whole structural chemistry. Secondly ,the thesis spotlights on the relationship between symmetry and selection rules, advises teachers to give necessary explanation for selection rules to students and point Out shortcomings in the present textbooks that don抰 list out an important rule ,the Laporte selection rule. Actually, this rule must be observed in both L桽 coupling and i梚 coupling. Thirdly, on the base of geometrical symmetry of molecules, the thesis adopts group theory method to determine hybrid orbitals?type and construct wavefunctions and discusses some parameters?dynamic effect on bond strength of orbitals, angles between different orbitals as well as transforms from subgroups to groups. Then, it explores the disputable problem relating to hybrid orbitals of trigonal bipyraniid molecules. In the general documents ,the cited hybrid orbitals don抰 conform to angle formula. In addition, this thesis I M~3TER S THES~ resorts to special parameter of bond functions which makes these hybrid orbitals satisfy the formula. Fourthly, it discusses the application of symmetry in determining degenerate MOs and simplizing quantization calculations, makes a comparatively useful and systematic exposition on the symmetry symbols of a double梐tomed molecule抯 electric terms,then elaborates proofs of symmtry matching which is an important issue in structural chemistry teaching. Finally, the thesis discusses symmetry抯 application in determining the type and number of canonical vibrations ,constructing vibrational patterns and determining molecular structure.