课程名称︰化学键 课程性质︰化学系大一以上选修 课程教师︰王瑜、郑原忠 开课学院：理学院 开课系所︰化学系 考试日期（年月日）︰2011.06.24 考试时限（分钟）：120mins 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : Chemical Bonding Spring, 2011 Final Exam Date: 6/24/2011 1. (8%) Determine the structure and point group of each of the molecules in the following: (a) SO3 2-, (b) BrF5, (c) ClF3, and (d) XeO3. 2. Consider SO3 2-, BrF5, and ClF3. Answer the following questions for each of the molecules. (a) (4% x 3) Find the reducible representation for σ bonding in the system and determine the irreducible symmetry representations. Find the possible a hybridizations for the center atom. List all possible hybridizations in your answer. (b) (4% x 3) Sketch the symmetry-adapted ligand-group orbitals, and use the results to construct a qualitative MO energy-level diagram. Explain your selection of hybrids and energy levels. 3. Consider SO32 and ClF3, and answer the following questions for each of them. (a) (4% x 2) Find the symmetry of the π-bonds in the molecule. (b) (3% x 2) Determine the center atom hybridizations that can contribute to it bonding, and use the results to construct a qualitative MO energy-level diagram for π-bonding in the molecule. 4. (10%) Consider the π-bonds in the cyclopentadienyl ring. Use the 5 p orbitals as a basis set and answer the following questions using a character table: (a) How do they separate into subsets of symmetry-equivalent orbitals? Give the symmetry representation of each subset. (b) Sketch the 5 symmetry-adapted linear combinations (SALCs) and the energy level diagram. 5. Molecular orbitals of the H4 molecule can be constructed using SALC of the four H 1s orbitals. Answer the following questions: (a) (4%) Determine the MOs for a tetrahedral H-1s molecule. Sketch the energy level diagram and the electronic configuration. (b) (4%) Consider a “butterfly” H4 molecule whose Ha-Hb bond is slightly shortened and Hc-Hd bond is slightly stretched. Determine its MOs, and sketch the energy level diagram for the butterfly H4. You need to correctly assign the order of the energy levels, (c) (4%) Draw a correlation diagram between the MOs of the two H4 molecules. You needto correctly assign the relative energies. Hint: use two symmetry planes to correlate the MOs. (d) (4%) Do you expect the H4 molecule to exhibit Jahn-TelIer effects? Do you expect the H4+ molecular cation to exhibit stronger or weaker Jahn-Teller effects? Use the correlation diagram to explain your answer. For simplicity, we ignore all other distortions. 6.(10%) Determine how the d-orbitals split in each of the following environments: (a) trigonal bipyrarmidal, and (b) square planar. Use a crystal field model to determine the relative energies. 7. (12%) Consider bonding between ligands and d-orbitals of a transition metal ion in an octahedral complex. Generally, the spcctrochcmical series follows the trend: 1,2-dimethylcyclo-3,5-hexadiene (two methyl group is in the same direction) to (2E,4Z,6E)octatriene π-donor ligands < pure σ-donor ligands < π-acceptor ligands. Apply the 1igand field theory to explain the trend. 8.(10%) The thermal electrocyclic reaction of hexatriene derivatives follows the following regioselection rules: Construct correlation diagrams for both the conrotatory and disrotatory reaction mechanism to explain the selectivity. 9. (3% each) Briefly explain the trends depicted in the following: (a) Wavelength of absorption maxima in LTV/Vi: [CoC16]3- > [CoF6]3 -> [Co(NH3)6]3+ > [Co(CN)6]3-. (b) Energy of absorption maxima in UV/Vis: [Ir(NH)6]3+ > [Rh(NH3)6]3+ > [Co(NH3)6]3+. (c) Lattice enthalpies of metal oxides with octahedral coordinations: VO> TiO> MnO > CaO. (d) v(CO) values in IR spectrum: [Mn(CO)6]+> [Cr(CO)6]> [V(CO)6]> [Ti(CO)6]2-. (e) Metal-Metal bond length: [Re2Cl8]2-> [Re2Cl8]- > Re2C18. (f) In octahedral [Cu(OH2)6]2+ Axial Cu-O bond length> Equatorial Cu-O bond length --

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