Group Theory and Symmetry：群理论与对称..ppt

Molecular Structure: The most powerful idea in chemistry is the idea of the three- dimensional structures of molecules. Two techniques have been invaluable in this regard. One is NMR (Nuclear ic Resonance), and the other is X-ray crystallography. X-ray crystallography has been intensively developed as a technique, which involves the ideas of symmetry of molecules. Understanding NMR also involves an understanding of symmetry. Group theory is also vital in understanding and predicting infra-red and Uv-visible (electronic) spectra. On the next two slides are structures plexes of metal ions determined by X-ray crystallography. These are shown simply to illustrate the power of X-ray crystallography in determining molecular structure. Determining such structures relies heavily on a knowledge of symmetry and group theory. Crystals of [Cd(DPP) 2 ](ClO 4) 2 (viewed through a microscope) X-ray diffractometer: Monochromatic X-ray source, . Cu K α X-rays X-ray diffraction pattern: The actual structure of the [Cd(DPP) 2] 2+ complex cation: DPP ligand Cd(II) cation N NN N DPP G. M. Cockrell, R. D. Hancock, D. G. VanDerveer, G. Zhang, R. P. Thummel, J. Am. Chem. Soc. , 2008 , 130 , 1420. Importance of X-ray crystallography uranium atom oxo (O 2- ) anion PDA ligand U-O bond = (6) ? N-U-O angle = (2) o Structure of [UO 2 (PDA)] determined by X-ray crystallography Nolan E. Dean, R. D. Hancock, M Frisch, C. Cahill, . Chem ., 2008 in the press. Unit cell of [UO 2 (PDA)] Structures of proteins. Facial symmetry Invariance to transformation as an indicator of facial symmetry: Mirror image