24 Jun 2013

Symmetry, Group Theory, and Computational Chemistry


Submitted by Joanne Stewart, Hope College

These Learning Objects were used in an advanced undergraduate chemistry course that used computational chemistry as an integrative tool to help students deepen their understanding of structure, bonding, and reactivity and practice their integrative expertise by addressing complex problems in the literature and in their own research. The course emphasized group theory and molecular orbital theory.

The one-semester course is taught every other year at Hope College. The students in the course are Juniors and Seniors and therefore have different amounts of previous chemistry experience. Most of the students are either planning to go to graduate school or pursue careers in chemistry. The class size is typically small (8-12) because students have options to take advanced courses in biochemistry or environmental science.

The learning goals for each object are summarized in the table.

Point Groups: Photosensitive Manganese Tricarbonyls

  • identify symmetry elements

  • assign point groups

Point Groups: Molecular Anions and the Extended Structure of Cs5AsP4Se12

  • draw Lewis structures and assign formal charges

  • learn the meaning of a nonstereochemically active lone pair

  • assign the point group of a challenging molecule

  • interpret layer-by-layer drawings of unit cells and demonstrate that the unit cell stoichiometry matches the empirical formula

IR Spectroscopy: Predicting the structures of rhodium carbonyl clusters

  • assign point groups to multinuclear rhodium carbonyl clusters

  • predict the number of IR-active CO stretching frequencies in bridging and terminal CO regions

Raman Spectroscopy of P-doped Sodium Silicide, Na4Si4

  • write and reduce a representation for all molecular motion for the tetrahedral (Si4)4- anion

  • predict the number of Raman-active vibrational modes for the tetrahedral (Si4)4- anion

  • assign the observed Raman spectrum of Na4Si4 by considering the effects of a descent in symmetry from the idealized Td point group

IR and Raman Spectroscopy of Cobalt Boronyl Tetracarbonyl, Co(BO)(CO)4

  • assign the point groups of 3 possible structures for Co(BO)(CO)4

  • predict the number of IR and Raman-active CO stretching frequencies for a each structure

A molybdenum carbonyl group theory question

  • assign the point group of two molybdenum isomers

  • use CO and CN stretching frequencies to assign isomer structures

  • use knowledge of electronic and steric effects to rationalize the formation of the two isomers

IR and Raman Spectroscopy of the Pentabromide anion

  • write and reduce a representation for all molecular motion for the V-shaped (Br5) anion

  • predict the number of IR and Raman-active vibrational modes

  • write and reduce a representation for the subset of stretching modes in the V-shaped (Br5) anion

  • predict how many peaks would appear in the Raman spectrum

Using Computational Chemistry to discuss backbonding to CO

(The Great Backdonation Challenge)

  • explain the effect of changing the metal on the CO stretching frequencies of a metal carbonyl complex

  • understand the role of σ and π donors/acceptors in modifying the amount of π backdonation into a trans CO ligand

  • predict the degree of backdonation into a trans carbonyl that will be observed with an unfamiliar ligand

  • perform DFT calculations to find the minima and vibrational frequencies of a molecule using WebMO/Gaussian

Molecular Orbitals and the Jahn Teller Distortion of XeF3- anion

  • derive the MO diagram of [XeF3]

  • apply a structural distortion to achieve either a T-shaped or Y-shaped molecule and consider the symmetry and orbital overlap changes that occur on an energy correlation diagram.

  • rationalize the most likely structure(s) of [XeF3] considering the impact of both steric and electronic factors



Thank you for grouping the Symmetry LOs since I want to update symmetry discussions and teaching in ny advanced inorganic class.

This collection is extremely useful, as I do have a strong computational component to the course. Thanks!

I'm using Matt Whited's in-class activity "Molecular Orbitals of Square-Planar Complexes" this year. It fits perfectly. I will add it to the collection in the future.