1. Using Computational Chemistry to Study a Reaction Pathway Jessica L. Case Super Chem II April 30, 2002

2. Goals of the Project Utilize Gaussian 98 and WebMO for various computational calculations: Geometry Optimizations Frequency Calculations Transition State Determination IRC Calculations to find Intermediate Structures Determine the energies of the reactants, intermediates, transition state, and product Use these methods to determine a reaction pathway Draw a calculated reaction coordinate diagram

3. Why this reaction? Studied it last summer as a possible monomer unit to form ladder polymers Reaction Under Study

4. Geometry Optimization: 2-methoxyfuran MethodBasis SetEnergy (H) Energy (kcal/mol) AM13-21+G -0.055206032-34.64230929 AM16-31+G(d) -0.055206032-34.64230929 AM1 6-311+G(d,p) -0.055206032-34.64230929 HF3-21+G -340.6059668-2.13734*10 5 HF6-31+G(d) -342.5083676-2.14927*10 5 HF 6-311+G(d,p) -342.5987805-2.14984*10 5 B3LYP3-21+G -342.6481147-2.15015*10 5 B3LYP6-31+G(d) -344.5377379-2.14945*10 5

5. Geometry Optimization: cyclobutylbenzyne MethodBasis SetEnergy (H) Energy (kcal/mol) AM13-21+G 0.273878653171.8614568 AM16-31+G(d) 0.273878653171.8614568 AM1 6-311+G(d,p) 0.273878653171.8614568 HF3-21+G -304.5375532-1.91100*10 5 HF6-31+G(d) -306.2532483-1.92177*10 5 HF 6-311+G(d,p) -306.3209326-1.92219*10 5 B3LYP3-21+G -306.5968457-1.92393*10 5 B3LYP6-31+G(d) -308.2918719-1.93456*10 5

6. Geometry Optimization: product* MethodBasis SetEnergy (H) Energy (kcal/mol) AM13-21+G 0.171341699107.5185441 AM16-31+G(d) 0.171341699107.5185441 AM1 6-311+G(d,p) 0.171341699107.5185441 HF3-21+G -645.1633345-4.04846*10 5 HF6-31+G(d) -648.7899777-4.07122*10 5 B3LYP3-21+G -649.2513117-4.07412*10 5 B3LYP6-31+G(d) -652.8390400-4.09663*10 5

7. Frequency Calculations MoleculeMethodBasis SetZPE (H) 2-MFHF3-21+G0.108346 2-MFHF6-31+G(d)0.108148 2-MFB3LYP6-31+G(d)0.101644 CBBHF3-21+G0.116369 CBBHF6-31+G(d)0.115783 CBBB3LYP6-31+G(d)0.109457 ProductHF3-21+G0.230598 ProductHF6-31+G(d)0.230935 ProductB3LYP6-31+G(d) 0.215880

8. Locating the Transition State First, combine the numbering of the atoms in the two reactant structures Second, combine the Z-matrices of the two geometry optimized reactants Third, determine the approximate approach of the two molecules will take to react together to form the product Vary distance between reactants Vary intermolecular angles Vary dihedral angles

9. Lining Up the Reactants* HF / 6-31+G(d) R = 3 Angstroms E = -648.6805142 H R = 10 Angstroms E = -648.7616681 H R = 20 Angstroms E = -648.7615803 H R = 80 Angstroms E = -648.7615669 H 2-methoxyfuran: E = -342.5083676 H cyclobutylbenzyne: E = -306.2532483 H sum of reactants: E = -648.7616159 H

10. Determining the Transition State Structure Use the combined Z-matrix of the two reactants and the Z-matrix of the product as input The STQN method locates a transition structure with the QST2 keyword Utilizes the input structures to determine a structure of maximum energy in between the reactants’ and product’s structures

11. The Transition State* Two different inputs yielded very similar structures E 1 = -648.752134712 H = -4.07098452053*10 5 kcal/mol E 2 = -648.752134717 H = -4.07098452056*10 5 kcal/mol The transition state occurred at R = 2.999 Angstroms Frequency calculations yielded a zero point energy of 0.229644 H and one negative vibrational mode, which is expected for a transition state structure

12. Locating the Intermediates IRC Calculations Takes the calculated structure and force field from the optimized transition state and determines intermediate structures along the reaction path Varied the number of steps away from the transition state: 2 steps: E = -648.7522613 H 10 steps: E = -648.7555564 H 40 steps: E = -648.7571191 H

13. The Intermediate Structures*

14. Reaction Coordinate Diagram Energy (H) -648.7521347 -648.7899777  =0.0094812 -648.7616159  =0.037843 Reaction Coordinate

15. And with that, my academic career at Hope College is complete!!!