Reaction 2: (d) Consider the following reaction that proceeds via a concerted mechanism. Add arrows to indicate the movement of electrons. OCH3 OCH3 (e) The electrophile in the reaction in part (d) is ethylene (H2CCH2). Circle the orbital of the electrophile that must overlap with the nucleophile orbital in this reaction. (f) nonbonding lone pair OC-C OC-0 OC-H TC-C nonbonding p σ*C-C σ*C-0 σ*C-H π*C-C In going from reactants to products in the reaction in part (d), does entropy increase, decrease, or stay about the same?

5. Each of the following may participate in an elimination reaction, under the proper conditions. (a) Circle the alpha (a) carbon. (b) Circle the beta (B) carbon(s). (c) Draw the alkene product(s) that may form, with the new double bond between the a and B positions. (d) If more than one alkene product is possible, circle the most stable (Zaitsev) product. X tx + 3

4. The given mechanism tracks the transformation of a primary hydroxyl FG into an aldehyde carbonyl using the Swern oxidation ([0]) conditions. Examine the details of the mechanism, paying close attention to the lack of lone pairs, and then respond to the following questions. Note that "reaction arrow" refers to the arrows that separate the reaction steps. (a) Draw a box around the pE2 step (reaction arrow) of the mechanism. (b) Draw a star on any addition (Ad) step (reaction arrow) of the mechanism. (c) Draw a circle around any elimination (E) step (reaction arrow) of the mechanism. (d) When the Swern conditions are characterized as NOT over-oxidizing primary hydroxyl FGs into carboxyl FGs, to what step in the mechanism does this refer? (e) What is the leaving group for the pE2 step in this mechanism? What criteria is used to judge what makes this FG a good leaving group? H3C S=0 H3C H3C → OS- H3C CO2 CO CIO CH2 H3C H3C CH3 H3C H3C H3C CH3 H. H3C O CH3 H3C H NET3 H3C H3C H3C R R NET3

2) For the following reaction, draw the likely nucleophilic substitution mechanism and try to write out that mechanism in words as in the previous example. CI OH OH2