Identifying Nucleophiles and Electrophiles (a)

Identifying Nucleophiles and Electrophiles (b)

Nucleophile and Electrophile Strengths Nucleophiles Electrophiles An atom acting as a nucleophile “loses” electron density, so the less electronegative atom will be more stable as a positive atom, meaning it is more likely to act as a nucleophile. Empty p orbital vs. complete octet Oxygen is more elctronegative, making it less stable as a positive atom and thus more reactive (eager to lose the positive charge)

Arrow Pushing

Thermodynamics (a) Incomplete octet and charges in products, not in reactants Incomplete octet and charges in reactants, not in products π bond becomes a σ bond Weak C-Br bond (fourth shell orbital from Br) replaces stronger C-Cl bond (third shell orbital from Cl). Also, Br- is bigger and thus more stable than Cl-. π bond becomes a σ bond

Thermodynamics (b) Restriction of free rotation in product (modest change) Two molecules become one (major change) No significant change

Kinetics Modestly stable secondary carbocation, trans alkene is more stable than cis Very stable tertiary carbocation formed Each alkene reactant is disubstituted Hammond’s postulate relates intermediate (cation) energy to TS energy Modestly stable secondary carbocation, cis alkene is less stable than trans

Kinetics (2) Br- is second most stable anion I- is most stable anion Cations have same energy, anions are different Hammond’s postulate relates intermediate (anion) energy to TS energy Cl- is second least stable anion

Kinetics (3) Primary is most stable anion Tertiary is least stable anion Anions have different energy Hammond’s postulate relates intermediate (anion) energy to TS energy Secondary is second most stable anion

Free Energy Diagrams (a)

Free Energy Diagrams (b) How many steps are in this reaction?____3____ Which step is the rate limiting step?_second__ How many sets of intermediates are there?____2____ Is the reaction exergonic or endergonic?_exergonic_ Is ΔGº greater or less than 0?____less___ Are products or reactants favored at equilibrium? _products__