18 Apr 2014

A Graphical Approach to Ligand Group Orbitals

Submitted by Adam R. Johnson, Harvey Mudd College

It would be an understatement to say that I fell in love with molecular orbital theory as an undergraduate. My inorganic professor at Oberlin College, Marty Ackermann, introduced us to SALCs and group theory. Two years later, I plowed through all the math in Cotton’s book at MIT and then I got to (yes, GOT to) TA the course two of the following three years (LC member Betsy Jamieson was one of my first students). My approach to MO theory and LGO generation is intuitive and graphical. Although I teach projection operators, I tell my students “real practicing inorganic chemists” don’t calculate their MO diagrams, they derive them quickly, and usually on the back of a cocktail napkin.

When I began my independent teaching career, I wanted to teach my students how to form MO diagrams quickly and accurately without getting bogged down by the math. I tell students that if they wanted accurate results, they would need to run a Gaussian job, but if they wanted to know how many unpaired electrons and what the frontier orbital set was, they could do it while taking notes during the weekly seminar.

From 2001-2004, using my chem 104 students as guinea pigs, I developed my method for constructing LGOs and the resulting MO diagrams. My method is based on one introduced by Verkade (the Generator Orbital approach), but was significantly simplified, refined and adapted using ideas from many other sources, as well as my own continued use of and love of MO theory and their predictive power.

I began posting my worksheets and pencasts on this technique to VIPEr early on, but had been preparing a J. Chem. Educ. manuscript for more than a decade. It took a year-long sabbatical in Kyoto for me to finish dotting all the i’s, crossing all the t’s, and analyzing the assessment data, but that article outlines my approach to forming LGOs.