A Novel Computer Lab Experiment Studies of Diels-Alder Reactions Stanislaw Skonieczny and Mima Staikova Department of Chemistry, University of Toronto, Toronto, Ontario, Canada, M5S 3H6 Why are research and teaching linked ? research - an élite activity scholars and scientists held hostage in classrooms It is impossible to teach well without reflection, analysis, discussion. Relationship between research and teaching

The Diels-Alder Reaction: a diene + a dienophile transition state a cyclohexene derivative CHM 348F (Organic Reaction Mechanisms) : - Lectures - “Wet” labs - Computer labs

Dienes: Dienophiles:

The most important orbitals in molecules for reactivity are the two so-called frontier orbitals. These are called the HOMO and LUMO Molecular Orbitals - review LUMO = lowest unoccupied molecular orbital lowest energy orbital available LUMO receives electrons characteristic for electrophilic component HOMO = highest occupied molecular orbital electrons from the HOMO are donated most available for bonding most weakly held electrons characteristic for nucleophilic component

ethene HOMOLUMO butadiene HOMO-1HOMOLUMOLUMO+1 Molecular Orbital Analysis of Diels-Alder reaction

Molecular Orbital Analysis – cont. Therefore the reaction is said to be a "symmetry allowed"

energy difference larger, less overlap - lower stabilization energy difference smaller, more overlap - more stabilization Molecular Orbital Analysis – cont.

An example of a problem: Choose the best pair (one diene and one dienophile) and calculate the energies of HOMO and LUMO. HOMO: LUMO:

HOMO LUMO dienesdienophiles

An example of a problem: Choose the best pair (one diene and one dienophile) and calculate the energy difference. HOMO: LUMO:  E = – ( ) = Hartree = kcal/mol

dienesdienophiles LUMO HOMO

exo product endo product Experiment: exo product more stable by 1.9 kcal/mol E a lower for the endo product by 3.8 kcal/mol

The Undergraduate Computer Lab - UCL Chemistry Department  CHM 138 Introductory Organic Chemistry |  CHM 151 Chemistry: The Molecular Science  CHM 247 Introductory Organic Chemistry ||  CHM 348H Organic Reaction Mechanisms  CHM 379 Biomolecular Chemistry  CHM 415 Atmospheric Chemistry  CHM 441F Applications of Spectroscopy to Organic Structure Determination  CHM 443S Physical Organic Chemistry  CHM 447F Bio-Organic Chemistry

Linux Computer Cluster Zeus Zeus configuration *Main node: AMD Athlon 64 Dual with 4 GB memory and 250 GB HD *Computational nodes: 10 Dual Athlon CPUs at 2 GHz, each with 1 GB memory. courtesy of Scott Browning

Foundation of the project  WebMo Pro interactive computer interface Hope College, Holland, MI, US

CHM348 Diels – Alder Reactions Computational Experiment using Gaussian03 suit of programs and WebMo interface Before you begin: 1.Read these instructions beforehand and then start working. 2.You have to complete 7 calculation jobs: 3 jobs for Geometry Optimization – 2 Reactants, 1 Product 1 job for Transition State Optimization 1 job for Transition State Vibrations 2 jobs for Molecular Orbital Calculations – one for each Reactant. 3.All energies are calculated in Hartree (Atomic Unit for Energy) Conversion factor to kcal/mol: 1 Hartree = kcal/mol

Select the appropriate substituents in the periodic table and construct the substituted diene and dienophile for your reaction. Prepare a separate job for each reactant. Building the Reactant Structures – cont.

From the “Calculation” drop box select “Geometry Optimization”. Use “Theory”, “Basis set”, “Charge”, and “Multiplicity” as shown above. When ready, send your job for calculation with the right blue arrow. Job Options for Reactant and Product Geometry Optimization ( 3 jobs ) Job Options

When your job is calculated (it will take some time) it will show a “complete” status. Use the “view button” to see and evaluate the results and to use them for your next job preparation. Monitoring jobs progress

Evaluating Results Energy

HOMO Energy LUMO Energy To view orbital, click here:

Diene - HOMO Dienophile - LUMO Comparing HOMO – LUMO orbitals

Diels Alder Reaction Endo Product FURAN Malonic Anhydride Endo Transition State Energy

1.89 kcal/mol 0.51 kcal/mol B3LYP/6-31G Reaction progress

Methodological particularities:  calculations are performed at “research level”  each student has a different set of compounds, works independently.  project can be done in class or remotely at each student convenience.

Benefits to the educational process:  relates the theoretical knowledge of the students gained in the courses to real problems, from the real environment.

Benefits to the educational process:  relates the theoretical knowledge of the students gained in the courses to real problems, from the real environment.  facilitates the direct connection between macroscopic description of the chemistry phenomena and the microscopic world of molecular interactions that drive chemical processes.

Benefits to the educational process:  relates the theoretical knowledge of the students gained in the courses to real problems, from the real environment.  facilitates the direct connection between macroscopic description of the chemistry phenomena and the microscopic world of molecular interactions that drive chemical processes.  exposes the students to various theoretical methods and approaches in solving scientific problems as a parallel/alternative to the experimental approaches presented in the chemistry course.

Acknowledgments  Andrew P. Dicks  Scott Browning, Jamie Donaldson  Andrew Woolley  Frank Buries, Michael Yoo $$ Chemistry Department, University of Toronto $$ Instructional Technology Courseware Development Fund