Name _____________________________________W.05.215H Exam No. 3 Page 11a. Kami has found that hydrolysis of ketal A is very fast, but that hydrolysis of ketal B is does not proceed at all. Provide an explanation that discusses both acid/base chemistry and the mechanism of ketal hydrolysis.1b. Circle which conditions (thermal or photochemical) can be used to obtain product C in this electrocyclic ring opening reaction. Rationalize your answer with drawings of the FMOs associated with the thermal and photochemical reactions.1c. You learned last semester that the first step of an ozonolysis reaction involves the addition of ozone to an alkene. Rationalize this thermal reaction using FMO analysis of the two reactants.O3+ H2C CH2OOOH3CCH2CH3ThermalH3CCH2CH3orPhotochemicalFMO Rationale10210H3CO OCH3ONH3CO OCH3NO(A) (B)(C)8cat TsOH/H2Ono reactioncat TsOH/H2Ofast reactionNH3CO OCH3B undergoes protonation at the very basic pyridine nitrogen first (before at the less basic ketal) to make a cationic compound. A second protonation of one of the oxygens of the ketal to carry out the acetal hydrolysis is then much less favorable becuase the positive charge makes the O much less basic.NH3CO OCH3HNH3CO OCH3HHKetal hydrolysis2 pt protonation of N, 3 pt effect of protonation (pKa) of R–OH, 3 rel. to mech of ketal hydrolysisH3CCH2CH3thermal closing gives cisHOMO (thermal reaction)H3CCH2CH3HOMO (photochemical reaction)photochemical closing gives transO O O4 pi electrons•HOMO of ozoneLUMO of ethyleneWould get same result with HOMO of ethylene and LUMO of ozoneName _____________________________________W.05.215H Exam No. 3 Page 22. Provide an arrow pushing mechanism for the conversion of D to E (Org. Lett. 2004, 6, 3775) under (a) basic and (b) acidic conditions. Be sure to rationalize the stereochemistry of the product!!!FH3CH2COOOHOFH3CH2COO(D)(E)2a. Basic conditions(Reactants = 1. LDA, 2. H3O+)2b. Acidic conditions(Reactants = H3O+)1010ReactantsFH3CH2COOO–N(i-Pr)2HFH3CH2COOO–OFH3CH2COOHHH3O+HOFH3CH2COOHHSN2 with inversion of stereochemistryFH3CH2COOOHH–OH2+FH3CH2COOOHH+FH3CH2COOOHOH2H2O–H+FH3CH2COOOHH+HOFH3CH2COOHHH+H2OHOFH3CH2COOHHName _____________________________________W.05.215H Exam No. 3 Page 33. Complete the following reaction schemes.Org. Lett. 2004, 6, 111.PhPhOHN OOCH32. LDA,1. TsCl, NEt3ONOPh1. HCl in CH3OH/heat2. LiAlH43. H3O+1. LiAlH42. H3O+OO OTMSOTMSOO1. LDA2.3. TMSCl, pyridineClONEt3N NOClOrg. Lett. 2004, 6, 3671.88666N OOCH3Ph PhOOTMS3 pts for OH rather than OTMSN NHClOOHPhONPh–1 per transposition erreorName _____________________________________W.05.215H Exam No. 3 Page 44a. Draw a mechanism for the following reaction (Org. Lett. 2004, 6, 43).64b. Provide a brief rationale for why product F is obtained in this reaction rather than product G.N NHONSHS NHON SONHeat, 12 hr+(F)(G)12cat. NEt3HSN NHONSN NHO–NHNEt3SN NHO–NS NHO+NNThis can be rationalized based on comparing the two possible leaving groups for formation of F and G, respectively. The first (formed with F) is resonance stabilized while the second (formed with G) is not.NNNNversusNHName _____________________________________W.05.215H Exam No. 3 Page 5Consider the decarboxylation reaction shown below.XO–O+ CO2YXYHeatXOOYδ−δ−Structure of transition statefor this reaction5a. If the substituent X was changed from NO2 to CH3 (leaving everything else the same) would you expect this reaction to go faster or slower? Explain briefly – use reaction coordinate diagram to help with your explanation.5b. If the substituent Y was changed from NO2 to CH3 (leaving everything else the same) would you expect this reaction to go faster or slower? Explain briefly – use a reaction coordinate diagram to help with your explanation.5c. Would the product (H) to be more stable if (a) X = NO2 and Y = CH3 or (b) if X = CH3 and Y = NO2. Explain briefly.666(H)Rate is affected by the energy of the transition state. In transition state there is negative charge building up at the carbon adjacent to the ring where X is bound. This negative charge will be stabilized by electron withdrawing substituents, making the transition state lower in energy and the reaction faster. Therefore X = CH3 (edg) slower than X = NO2 (ewg).Energystarting materialtransition state for CH3 (higher energy)transition state for NO2 (lower energy)Answer: 1 point; Explanation: 3 points; Rxn Coordinate: 2 points–2 if the discussion involves product H rather than transition stateAgain, rate is affected by the energy of the transition state and there is a negative charge building up in this system in the transition state, so changing Y from NO2 (an ewg that stabilizes negative charge) to CH3 (an edg that destabilizes negative charge) should raise the energy of the TS and slow the reaction down.Energystarting materialtransition state for CH3 (higher energy)transition state for NO2 (lower energy)The product would be more stable when X = NO2 and Y = CH3. The X substituent is much closer to the carbon with the negative charge than the Y substituent. Therefore, it will have a greater ability to stabilize that charge (through both inductive and resonance effects) than the Y substituent.Answer: 2 points; Explanation: 4 points–2 if discussion involves TS rather than product HAnswer: 1 point; Explanation: 3 points; Rxn Coordinate: 2 points–2 if the discussion involves product H rather than transition