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  Home > JCE Print > Journal of Chemical Education > Issues > 2001  > January  >
Information • Textbooks • Media • Resources
Molecular Modeling Exercises and Experiments
Organometallic Computational Exercise: Semiempirical Molecular Orbital Calculations on (C6H6)Cr(CO)3 and (B3N3H6Cr(CO)3
James F. O'Brien
Department of Chemistry, Southwest Missouri State University, Springfield, MO 65804

Daniel T. Haworth
Department of Chemistry, Marquette University, Milwaukee, WI 53201

Cover
January 2001
Vol. 78 No. 1
p. 134
Abstract
A student exercise employing semiempirical molecular orbital calculations in the area of organometallic chemistry is presented. PM3 level calculations are applied to the ground-state structures of C6H6)Cr(CO)3 and (B3N3H6)Cr(CO)3. The calculations are generally successful in computing the known features of the ground-state structures. Comparison of the geometries computed for free and complexed C6H6 and B3N3H6 allow discussion of the reasons for the changes observed. The structures of the transition states for rotation of the rings with respect to Cr(CO)3 are also computed. These results permit calculation of the activation energies for the ring rotations. The activation energies computed at the PM3 level are 0.4 and 18.3 kcal/mol for (C6H6)Cr(CO)3 and (B3N3H6)Cr(CO)3, respectively. These results highlight the differences between the two molecules. Students are encouraged to comment on structural changes in the rings, on the phenomenon of ring rotation in these systems and others such as ferrocene, on the question of the aromaticity of the borazine ring, and on the effect of p back-bonding on the positions of the carbonyl stretching bands in the both complexes.
Supplement
An expanded version of the article and a student handout are available.
*  Contents JCE2001p0134W.doc, StudHandout.doc, PCSPro2.doc (MS Word)
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JCE2001p0134W.pdf

JCE2001p0134W.zip

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More Information
*  Citation
 O'Brien, James F.; Haworth, Daniel T. J. Chem. Educ. 2001 78 134.
*  Keywords
 Chromium; Computational Chemistry; Metal Carbonyls; Molecular Modeling / Dynamics; Organometallics; Teaching / Learning Aids
*  History
 Created:
Last Updated:		 November 30, 2000
August 31, 2005
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