Chemical Reactions Involve Changing Electronic Configuration• Electrons move (many orders of magnitude) faster than atoms.• So, as atoms move, electrons & orbitals are constantly responding.• One method for tracking/illustrating this: “Electron Pushing”• Not just useful for accounting; also shows intermediates along reaction path“Electron Pushing”OOROOH+ H2O+ ROHSimple but effective example:Base-catalyzed hydrolysis of acetyl ester.OORHOHOROOH HA tempting beginning…This does happen,but intermediate is very unstable.Some electron-pushing rules of thumb:• Retain all atoms, electrons, and charge• Avoid zwitterions (especially when related by proton transfer)• Avoid multiple charges on same molecule• Don’t take shortcuts; show all steps“Electron Pushing”Simple but effective example:Base-catalyzed hydrolysis of acetyl ester.HOHBOOROHBHOOROROHOBHORBHOOHour firstester intermediateSome electron-pushing rules of thumb:• Retain all atoms, electrons, and charge• Avoid zwitterions (especially when related by proton transfer)• Avoid multiple charges on same molecule• Don’t take shortcuts; show all steps“Electron Pushing”Simple but effective example:Base-catalyzed hydrolysis of acetyl ester.HOHBOHBHOOROOROROHOORBHOOHBHHOROOHBSome electron-pushing rules of thumb:• Retain all atoms, electrons, and charge• Avoid zwitterions related by proton transfer• Avoid multiple charges on same molecule• Don’t take shortcuts; show all stepsOOHHHORA“Electron Pushing”Acid-catalyzed hydrolysis of acetyl ester:HOHHOORAHOHOORAHOROHOH HAagain, tempting…our firstester intermediate…but too much charge.Some electron-pushing rules of thumb:• Retain all atoms, electrons, and charge• Avoid zwitterions related by proton transfer• Avoid multiple charges on same molecule• Don’t take shortcuts; show all steps“Electron Pushing”Acid-catalyzed hydrolysis of acetyl ester:HOHHOORAHOHOORAHOROHOH HAOROHHOHAOOHHORHAOOHHROHASome electron-pushing rules of thumb:• Retain all atoms, electrons, and charge• Avoid zwitterions related by proton transfer• Avoid multiple charges on same molecule• Don’t take shortcuts; show all steps“Electron Pushing”Acid-catalyzed hydrolysis of acetyl ester:HOHHOORAHOHOORAHOROHOH HAOROHHOHAOOHHORHAOOHHROHAOOHROHHADiscussion QuestionIf catalyzed rate is determined, in part, by stability of the initial ester intermediate, for which of these reactants would hydrolysis be more susceptible to catalysis by added acid? Which would be more susceptible to added base?OORNOORNHDiscussion QuestionIf catalyzed rate is determined, in part, by stability of the initial ester intermediate, for which of these reactants would hydrolysis be more susceptible to catalysis by added acid? Which would be more susceptible to added base?OORNOORNHIn base, ester intermediate looks like:OORNHOOORNHHOhydrogen bonding stabilizes anion;facilitates base catalysisDiscussion QuestionIf catalyzed rate is determined, in part, by stability of the initial ester intermediate, for which of these reactants would hydrolysis be more susceptible to catalysis by added acid? Which would be more susceptible to added base?OORNOORNHIn acid, ester intermediate looks like:hydrogen bonding stabilizes cation;facilitates acid catalysisOORNHOORNH H(no H-bonding that isn’t already present in unprotonatedstate)Molecular Orbital (MO) TheoryMO Theory explains energy of bonding in terms of “orbital mixing”.HHHHHHC-C bond in ethane built fromcomponent atomic orbitals.equalsHHHHHHCsp3Csp3+EΔEupperMOΔElowerMOTypically,ΔEupperMO> −ΔElowerMOBecause energetics of system are determined by energies of electrons, orbital mixing stabilizes this bond.Molecular Orbital (MO) TheoryMO Theory explains difference in effect of substitution oncarbocation and carbanion stability.RRR(+ or -)stability for R3C+: 3° > 2° > 1° > CH3stability for R3C-: 3° < 2° < 1° < CH3RRHHHFor each neighboring C-H bond in R3C+,+C-H σCpEach neighboring C-H σstabilizes empty Cporbital(ΔElowerMO) in cationMolecular Orbital (MO) TheoryMO Theory explains difference in effect of substitution oncarbocation and carbanion stability.RRR(+ or -)stability for R3C+: 3° > 2° > 1° > CH3stability for R3C-: 3° < 2° < 1° < CH3RRHHH-C-H σCpBecauseΔEupperMO> ΔElowerMO, anion is destabilizedFor each neighboring C-H bond in