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Sponsor: Professor Vince DeTuri, References from Professor Heinz Koch
• Single Proton Nucleus
• N. Mass: 1.6726x10-27 kg
• Lightest Element
Proton (1.6726x10-27 kg)
Neutron (1.6749x10-27 kg)
• Added Neutron
• N. Mass: 3.3475x10-27 kg
• 200.13% more massive
than Hydrogen Atom.
• Two added Neutrons
• N. Mass: 5.0224x10-27 kg
• 300.28% more massive
than Hydrogen Atom.
• Experimental Observation: Reactions involving Hydrogen transfer go faster than Deuterium transfer, which is faster still than Tritium.
• Hydrogen, deuterium, and tritium have different masses but behave the same electronically.
Energy
• Getting from point A to point B requires Energy.
ΔE
• Deuterium sits lower in energy than Hydrogen, and Tritium sits lower still.
H
D
T
• This means that Hydrogen requires the least ΔE to get over the energy barrier.
• The result is that Hydrogen will transfer the fastest, and these relative rates can be experimentally observed.
B
A
Reaction ProgressXH Y- (X H Y)- X- HY
• Professor Heinz Koch began studying the reaction of certain alkenes with methoxide ion.
The Alkene Benzyl-β,β-difluorostyrene
-
HydrogenCarbonFluorineOxygen
The Alkane
• Proton Transfer: Can study isotope effects…
• However: No isotope effects were observed!
+ (E) & (Z) Isomers
Methoxide/Methanol
• The reaction mechanism can be summarized with a theoretical energy diagram:
The Alkene
(E) & (Z) Isomers
The Alkane
-Carbanion
H-Bonding
Energy
• Organic Chemistry: Make Unexpected Observations
• Cannot observe proton, deuteron, and trition transfer during reactions!
• Can determine kinetic isotope effects through chemical kinetics.
• Physical Chemistry: Model Unexpected Observations• Cannot easily determine reaction rates and kinetic isotope effects.
• Can observe reaction pathways, intermediates, product analysis, and relative energetics!
Reaction Progress
Energy
• Interested only in proton exchange right now.
Too Difficult to Calculate!
• Using b3lyp/6-31g+(d,p) level of theory for optimization to support energy diagram.
Calculate the Optimization Energies of:
Energy Calculations
E
Encounter Complex
Transition State
Hydrogen Bound
0 kJ/mol
14 kJ/mol
30 kJ/mol (approx)
• Many TS calculations crashed; many approximations were made.
• Find an accurate Transition State.• Does the TS connect the EC and HB?
• Build up the solvent system.
• Four Solvating methanol molecules…
• Use solvent wrapping technique.
• Try different solvents.
• Try different carbanion systems.
• Model the actual system.
Pentafluorobenzene 9-Methyl-Fluorene
Sponsor: Professor Vince DeTuri, References from Professor Heinz Koch
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