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Story of the Pentamethyl- Cyclopentadienyl Cation C 5 Me 5 + Roger L. DeKock Department of Chemistry and Biochemistry Calvin College, Grand Rapids, MI.

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Presentation on theme: "Story of the Pentamethyl- Cyclopentadienyl Cation C 5 Me 5 + Roger L. DeKock Department of Chemistry and Biochemistry Calvin College, Grand Rapids, MI."— Presentation transcript:

1 Story of the Pentamethyl- Cyclopentadienyl Cation C 5 Me 5 + Roger L. DeKock Department of Chemistry and Biochemistry Calvin College, Grand Rapids, MI

2 The Stable Pentamethyl- cyclopentadienyl Cation Angewandte Chemie Int. Ed. 2002, 41, No. 8, , by Joseph B. Lambert, Lijun Lin, and Vitaly Rassolov. Antiaromatic, 2n Aromatic, 2n+2

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4 The Stable Pentamethyl- cyclopentadienyl Cation “Elusive Carbocation Isolated as a Solid” Chemical and Engineering News, April 29, Four unusual features –Stable –Unequal C-C bond lengths around the ring –Me-C-C-Me dihedral angle nearly 110° –Singlet state, no unpaired spins

5 The Fall-Out Corrigendum, Issue No. 10 Note from the Editors: unfortunately the results reported in the communication “The Stable Pentamethylcylopentadienyl Cation” by Joseph B. Lambert et al. in issue 8/2002 (pp ) must be corrected. Guy Bertrand et al. quickly discovered that not the pentamethyl- cylopentadienyl cation but pentamethyl- cylopentenyl cation was prepared 

6 The Fall-Out Editorial (Issue No. 13, page 2211) “And Hückel Was Correct After All―A Withdrawal and an Apology” by Dr. Peter Gölitz, Editor “The Stable Pentamethylcyclopentdienyl Cation Remains Unknown”, by M. Otto, D. Scheschkewitz, T. Kato, M. M. Midland, J. B. Lambert, and G. Bertrand. Angewandte Chemie Int. Ed. 2002, 41, No. 13,

7 The Fall-Out “Comment on the X-Ray Structure of Pentamethylcyclopentadienyl Cation” by Thomas Müller, Angewandte Chemie Int. Ed. 2002, 41, No. 13, “Statement” by Joseph B. Lambert, Angewandte Chemie Int. Ed. 2002, 41, No. 13, 2278.

8 The Fall-Out “The crystal structure of ‘pentamethyl- cylopentadienyl cation’ is that of the pentamethylcyclopentyl cation” by Jamie N. Jones, Alan H. Cowley, and Charles L. B. Macdonald, Chemical Communications, 2002,

9 Connection to Pedagogy Two-week computational chemistry module in advanced organic chemistry and in biophysical chemistry Week 1 –Before lab session students are given the original article and the C&EN article to read, along with some notes –In lab students complete computational exercises, SHMO, Gaussian, Spartan, etc. Start with C 5 H 5 +, later add methyl groups –Examine nature of important molecular orbitals

10 Highest Occupied MO

11 Week 1 Laboratory Cont’d. –Examine both singlet and triplet electronic configurations, especially with respect to dihedral angle of interest –Compare theory and experiment, consider crystal packing forces, etc.

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13 Week 2, Laboratory Pointers to subsequent literature Complete additional theoretical studies on distorted molecule Strengths of this approach –Fit a short segment of computational chemistry into a larger course –Connects to prior study in organic chemistry –Practice in reading original literature

14 Student Learning Outcomes Read literature with a critical eye Learn about scientific method, how it is self correcting Use computational chemistry software Interpret output from software Write a formal report on the results of the two week project

15 Additional Information Teaching materials This PowerPoint

16 Acknowledgements Lee Heeringa Calvin College


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