W2013CHM2311 Part 4c Notes

Assign symmetry labels to the group orbitals in c2v 1

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Unformatted text preview: essler and Tarr MO Diagram: Focusing on Interac0ons B2u B3u B1u 3 ag 2p Ag B2u B3g -10.7 ev B3u 2p G O s -15.9 eV B1u B2g -19.5 eV 2s Ag 2 ag B1u 2s GOs 1ag C OCO O O -32.4 eV Ag See Fig. 5 ­26, p.157 in Miessler and Tarr MO Diagram: Focusing on Interac0ons B1u 3b1u B3u 3 ag The degenerate orbital is not shown 2b3u 2b2u 2p B2u B2u Ag B3u B3g 1b3u Ag 2s 1b2u 2p G O s B2g 2b1u B1u 2 ag 1ag C B1u OCO 2s GOs O O Ag See Fig. 5 ­26, p.157 in Miessler and Tarr MO Diagram of CO2 B1u 3b1u B3u 3 ag The degenerate orbital is not shown 2b3u 2b2u 2p B2u B2u 1b3g Ag B3u 1b2g 2p GOs B3g π 1b3u 2s Ag 1b2u 2b1u B1u B2g σ 2 ag B1u 1b1u C C 1ag O C O 2s GOs O O Ag Fig. 5 ­26, p.157 in Miessler and Tarr Energies of MOs of CO2 You should be able to figure out the atomic orbitals from which each of these molecular orbitals was derived and also derive their shapes. Although spectroscopic data or theore0cal calcula0ons is needed to determine exact order of molecular orbital energies, we can make a good guess as to the order based on number of nodes in each MO and knowledge of AO and GO energies. General approxima0ons are: a)  σ orbitals will be more stabilizing (if bonding) or destabilizing (if an0bonding) than the π orbitals. b)  the greater the number of nodes, the higher the energy of the molecular orbitals ↳  the order of energies of the σ orbitals can be approximated based on the # of nodes Energies of MOs of CO2 The order of energies of the σ orbitals can be approximated based on the # of nodes: MO Theory for Non ­Linear Triatomics (e.g., H2O) C2 z The approach is the same: 1.  Assign point group 2.  Define the coordinate system ↳  By conven0on the z axis is the principle rota0on axis. In water, the z ­axis bisects the H ­O ­H angle and the molecule is in the xz plane. O Ha Hb Φ1 O Ha Hb Φ2 σv(xz) O H H 3.  Group the terminal atoms into symmetry equivalent sets – i.e., SALCs. ↳  Two H 1s orbitals combine in ­phase an out ­of ­ phase. The energies of the resul0ng GOs are very similar – i.e., the interac0on is very weak. 4.  Sketch t...
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