My additional comments, questions are colored in blue in the following slides.

Transcription

1 My additional comments, questions are colored in blue in the following slides. Do not forget to work the assigned HW from the text that is also posted on the boardlist. I will post my answers to these Q s on the boardlist Monday morning.

2 Symmetry and MOs 1. AO symmetry constrained by point group of molecule H N H H p 64

3 Symmetry and MOs 1. AO symmetry constrained by point group of molecule 2. Symmetry and bonding (nothing new) sigma bonding could overlap with AO but not

4 Symmetry and MOs 1. AO symmetry constrained by point group of molecule 2. Symmetry and bonding (nothing new) pi bonding could overlap with AO but not

5 Symmetry and MOs 1. AO symmetry constrained by point group of molecule 2. Symmetry and bonding (nothing new) 3. Valence bond vs Symmetry adapted MO s (SALCs) s, p x, p y, p z hybridization F SALC s from symmetry F F F

6 T d symmetry adapted linear combinations formed from 4 equivalent H 1s orbitals in CH 4. p 808

7 Symmetry and MOs 1. AO symmetry constrained by point group of molecule 2. Symmetry and bonding (nothing new) 3. Valence bond vs Symmetry adapted MO s (SALCs) s, p x, p y, p z hybridization bonds = overlap of sp 3 with H 1s F F F F SALC s from symmetry bonds = overlap of H 1s SALC s with central atom AO s

8 Example: NH 3 1. point group symmetry = C 3v 2. H1s SALC s 3. N basis set and symmetries p Number of MO s of each symmetry type 5. Construct MO diagram, label MO s

9 Example: NH 3 p 54 3a 1 2e 2a 1 p 64 1e

10 Example: H 2 O C 2v 1. point group symmetry = 2. H1s SALC s 3. O basis set and symmetries 4. Number of MO s of each symmetry type 5. Construct MO diagram, label MO s Sketch the resulting MO s for water. Rank them energetically

11 Example: H 2 O Assign symmetry labels to these MO s of water. Rank them energetically. Which of these is the HOMO? Which the LUMO of water?

12 Example: BH 3 Construct a symmetry-based MO diagram for this molecule. Label all MO s and add the appropriate number of electrons. Identify the HOMO and LUMO of BH 3. Is this molecule a Lewis acid or base? Which MO is responsible for this behavior.

13 Now do a symmetry-based MO diagram for CH 4. Identify the HOMO and LUMO in this molecule. Which ionic form of CH 4 is predicted to have the longer C-H bond: CH 4 + or CH 4-? In lecture we discussed excited state methane, CH 4 *. Label a quantized transition in your MO diagram that could represent the formation of CH 4 *.

14 Do these diagrams make more sense? p 49 p 59 p 50 Use symmetry to understand how C 2s can contribute to all of the nσ MO s but not the nπ MO s? Sketch the some of the MO s: 2π of CO, 1σ, 2σ of Icl. Which ion is predicted to have a longer I-Cl bond: ICl + or ICl -?

15 Sketch an MO diagram for SF 6 S normal basis set Approximate the 6 F s as a single lone pair only.

16 Construct an MO diagram for an octahedral transition metal complex. Like PtCl 6 2- For your basis set use 1. all s, p, d orbitals on the metal. 2. count each Lewis base as a lone pair of electrons 3. consult the back of the book for SALC s

17 Use appropriate SALC s from the back of the book to construct the 6 SALC s that would result from the 6 resonating p-orbitals on benzene. Hin #1: take a bird s eye view down on top of the molecule. Hint #2: Remember our idea of patterns and standing waves. Arrange these 6 SALC s according to energy (lowest to highest).

18 Piano stool transition metal complexes James Burgio, Nicholas M. Yardy, Jeffrey L. Petersen, and Frederick R. Lemke Organometallics 2003, 22,