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

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Presentation transcript:

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

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

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

Geometry Optimization: 2-methoxyfuran MethodBasis SetEnergy (H) Energy (kcal/mol) AM13-21+G AM16-31+G(d) AM G(d,p) HF3-21+G *10 5 HF6-31+G(d) *10 5 HF G(d,p) *10 5 B3LYP3-21+G *10 5 B3LYP6-31+G(d) *10 5

Geometry Optimization: cyclobutylbenzyne MethodBasis SetEnergy (H) Energy (kcal/mol) AM13-21+G AM16-31+G(d) AM G(d,p) HF3-21+G *10 5 HF6-31+G(d) *10 5 HF G(d,p) *10 5 B3LYP3-21+G *10 5 B3LYP6-31+G(d) *10 5

Geometry Optimization: product* MethodBasis SetEnergy (H) Energy (kcal/mol) AM13-21+G AM16-31+G(d) AM G(d,p) HF3-21+G *10 5 HF6-31+G(d) *10 5 B3LYP3-21+G *10 5 B3LYP6-31+G(d) *10 5

Frequency Calculations MoleculeMethodBasis SetZPE (H) 2-MFHF3-21+G MFHF6-31+G(d) MFB3LYP6-31+G(d) CBBHF3-21+G CBBHF6-31+G(d) CBBB3LYP6-31+G(d) ProductHF3-21+G ProductHF6-31+G(d) ProductB3LYP6-31+G(d)

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

Lining Up the Reactants* HF / 6-31+G(d) R = 3 Angstroms E = H R = 10 Angstroms E = H R = 20 Angstroms E = H R = 80 Angstroms E = H 2-methoxyfuran: E = H cyclobutylbenzyne: E = H sum of reactants: E = H

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

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

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 = H 10 steps: E = H 40 steps: E = H

The Intermediate Structures*

Reaction Coordinate Diagram Energy (H)  =  = Reaction Coordinate

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