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William A. Goddard, III, wag@kaist.ac.kr

Lecture 20, November 18, 2009. Nature of the Chemical Bond with applications to catalysis, materials science, nanotechnology, surface science, bioinorganic chemistry, and energy. Course number: KAIST EEWS 80.502 Room E11-101 Hours: 0900-1030 Tuesday and Thursday.

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William A. Goddard, III, wag@kaist.ac.kr

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  1. Lecture 20, November 18, 2009 Nature of the Chemical Bond with applications to catalysis, materials science, nanotechnology, surface science, bioinorganic chemistry, and energy Course number: KAIST EEWS 80.502 Room E11-101 Hours: 0900-1030 Tuesday and Thursday William A. Goddard, III, wag@kaist.ac.kr WCU Professor at EEWS-KAIST and Charles and Mary Ferkel Professor of Chemistry, Materials Science, and Applied Physics, California Institute of Technology Senior Assistant: Dr. Hyungjun Kim: linus16@kaist.ac.kr Manager of Center for Materials Simulation and Design (CMSD) Teaching Assistant: Ms. Ga In Lee: leeandgain@kaist.ac.kr Special assistant: Tod Pascal:tpascal@wag.caltech.edu EEWS-90.502-Goddard-L15

  2. Schedule changes Nov. 18, Wednesday, 1pm, L20, additional lecture room 101 Nov. 19, Thursday, 9am, L21, as scheduled Nov. 24, Tuesday, 9am, L22, as scheduled Nov. 26, Thursday, 9am, L23, as scheduled Dec. 1, Tuesday, 9am, L24, as scheduled Dec. 2, Wednesday, 3pm, L25, additional lecture, room 101 Dec. 3, Thursday, 9am, L26, as scheduled Dec. 7-10 wag lecturing Seattle and Pasadena; no lectures, Dec. 11, Friday, 2pm, L27, additional lecture, room 101 EEWS-90.502-Goddard-L15

  3. Last time EEWS-90.502-Goddard-L15

  4. Summary Ferroelectrics • The P-QEq first-principles self-consistent polarizable charge equilibration force field explains FE properties of BaTiO3 • BaTiO3 phases have the FE/AFE ordering. Explains phase structures and transitions • Characterized 90º and 180º domain walls: Get layered structures with spatial charges • The Oxygen vacancy leads to linearly ordered structures  dendritic patterns. Should dominate ferroelectric fatigue and dielectric breakdown EEWS-90.502-Goddard-L17

  5. Woodward-Hoffmann rulesorbital symmetry rulesFrontier Orbital rules Roald Hoffmann Certain cycloadditions occur but not others 2s+2s 2s+4s 4s+4s EEWS-90.502-Goddard-L17

  6. Woodward-Hoffmann rulesorbital symmetry rulesFrontier Orbital rules Certain cyclizations occur but not others conrotatory disrotatory disrotatory conrotatory EEWS-90.502-Goddard-L17

  7. 2+2 cycloaddition – Orbital correlation diagram GS Allowed Forbidden ES EEWS-90.502-Goddard-L17

  8. WH rules – 2 + 4Ground State A A S A S S Allowed EEWS-90.502-Goddard-L17

  9. WH rules – 2 + 4Excited State A A S Forbidden A S S EEWS-90.502-Goddard-L17

  10. Summary WH rules cycloaddition 2n + 2m n+m odd: Thermal allowed Photochemical forbidden n+m even: Thermal forbidden Photochemical allowed n=1, m=1: ethene + ethene n=1, m=2: ethene + butadience (Diels-Aldor) EEWS-90.502-Goddard-L17

  11. S WH rules – cyclization-GS A A A S A A S Forbidden Allowed A S S A S A S S Rotation, C2 Reflection, s EEWS-90.502-Goddard-L17

  12. S A A S S A A S WH rules – cyclization-ES A A S A Allowed Forbidden A S S S Rotation, C2 Reflection, s EEWS-90.502-Goddard-L17

  13. Summary WH rules cyclization 2n n odd: thermal disrotatory Photochemical conrotatory n even: Thermal conrotatory Photochemical disrotatory n=2  butadiene n=3  hexatriene EEWS-90.502-Goddard-L17

  14. GVB view reactions Reactant HD+T H D T Product H+DT Goddard and Ladner, JACS 93 6750 (1971) EEWS-90.502-Goddard-L17

  15. GVB view reactions Reactant HD+T H D T During reaction, bonding orbital on D stays on D, Bonding orbital on H keeps its overlap with the orbital on D but delocalizes over H and T in the TS and localizes on T in the product. Thus highly overlapping bond for whole reaction Nonbonding Orbital on free T of reactant becomes partially antibonding in TS and localizes on free H of product, but it changes sign Product H+DT EEWS-90.502-Goddard-L17

  16. GVB view reactions Reactant HD+T H D T Bond pair keeps high overlap while flipping from reactant to product Transition state nonbond orbital keeps orthogonal, hence changes sign Product H+DT H D T EEWS-90.502-Goddard-L17

  17. Some old and some New material EEWS-90.502-Goddard-L17

  18. GVB analysis of cyclization (4 e case) Move AB bond; Ignore D; C changes phase as it moves from 3 to 1 4 VB orbitals: A,B,C,D reactant φB φA φB φA φB φC 2 3 4 1 φD φC φA φD φC 2 3 φD 4 1 φB φA 2 3 Now ask how the CH2 groups 1 and 4 must rotate so that C and D retain positive overlap. Clearly 4n is conrotatory φC φD 1 4 EEWS-90.502-Goddard-L17

  19. GVB analysis of cyclization (6 e case) EEWS-90.502-Goddard-L17

  20. Apply GVB model to 2 + 2 4 VB orbitals:A,B,C,D reactant Transition state: ignore C φB φA φA φB φC φD φD φB φD Nodal plane 4 VB orbitals product φA φC \ φC EEWS-90.502-Goddard-L17

  21. Transition state for 2 + 2 2 1 3 4 2 1 3 4 Transition state: ignore C Orbitals A on 1 and B on 2 keep high overlap as the bond moves from 12 to 23 with B staying on 2 and A moving from 1 to 3 φB 2 1 φA Orbital D must move from 3 to 1 but must remain orthogonal to the AB bond. Thus it gets a nodal plane The overlap of D and C goes from positive in reactant to negative in product, hence going through 0. thus break CD bond. 3 4 φD Nodal plane φC Reaction Forbidden EEWS-90.502-Goddard-L17

  22. GVB model fast analysis 2 + 2 φB φD φA \ φC 4 VB orbitals:A,B,C,D reactant Move A from 1 to 3 keeping overlap with B Simultaneously D moves from 3 to 1 but must change sign since must remain orthogonal to A and B 2 1 φA φB φC φD 3 4 C and D start with positive overlap and end with negative overlap. Thus break bond  forbidden EEWS-90.502-Goddard-L17

  23. Next examine 2+4 EEWS-90.502-Goddard-L17

  24. GVB 2+4 φC φB φD φA 2 3 1 4 6 5 φE φF φA φB φD φC 2 3 1 4 6 5 φE φF 1. Move AB bond; Ignore D; C changes phase as it moves from 3 to 1 EEWS-90.502-Goddard-L17

  25. GVB 2+4 2. Move EF bond; C changes phase again as it moves from 1 to 5 φA φB φD φC 2 3 1 4 φA φB φD 2 3 6 5 1 4 φE φF φE φC 3. Now examine overlap of D with C. It is positive. Thus can retain bond CD as AB and EF migrate 6 5 φF Reaction Allowed EEWS-90.502-Goddard-L17

  26. GVB 2+4 2. Move EF bond; C changes phase again as it moves from 1 to 5 φC φB φD φA 2 3 1 4 6 5 φE φF φA φB φD φC 2 3 1 4 φA φB φD 2 3 6 5 1 4 φE φF 3. Examine final overlap of D with C. It is positive. Thus can retain bond CD as AB and EF migrate φE 1. Move AB bond; Ignore D; C changes phase as it moves from 3 to 1 φC 6 5 φF Reaction Allowed EEWS-90.502-Goddard-L17

  27. New material EEWS-90.502-Goddard-L17

  28. Transition metals Aufbau (4s,3d) Sc---Cu (5s,4d) Y-- Ag (6s,5d) (La or Lu), Ce-Au EEWS-90.502-Goddard-L17

  29. Ground states of neutral atoms EEWS-90.502-Goddard-L17

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