In Class Test 1 Chapters 14 16 Prof Jason J Chruma Sichuan University Organic Chemistry I 2 Course Number 203113030 Spring 2014 Group Number KEY Initial Score 15 Final Score 15 Name Student Number Name Student Number 1 2 3 4 5 6 7 8 1 Rank the following dienes in order of decreasing heat of hydrogenation highest heat of hydrogenation to lowest 1 pt ABCD D B A C 2 Provide molecular orbital diagrams for the HOMO LUMO HOMO and LUMO for octa 1 3 5 7 tetraene 1 5 pt HOMO 3 nodes LUMO HOMO 4 nodes LUMO 5 nodes 3 Provide all potential products of the following hydrobromination clearly indicate stereochemistry where appropriate 1 pt HBr Br EN Br EN EN Br Br 2 4 Predict the major product for each of the following cycloadditions indicate relative stereochemistry where appropriate 2 pt A O O O heat O O O H H B heat NC CN CN CN EN C O O h O O EN H D BrO Br O h BrO Br O 5 Predict the product for the following electrocyclic reactions Clearly indicated relative stereochemistry and whether the bond formation breakage event is conrotatory or disrotatory 1 pt A B heat EN conrotatory heat EN DISROTATORY 3 6 A Predict the product for the following sigmatropic rearrangement Clearly indicate stereochemistry as appropriate 0 5 pt OH heat 3 3 H H OH H H O major tautomer B The rate of the above 3 3 sigmatropic rearrangement is dramatically increased if the alcohol is first deprotonated to the alkoxide Suggest an explanation for this rate enhancement 0 5 pt The only way to increase the intrinsic rate of a reaction is to decrease the activation energy barrier the energy distance between starting material and transition state So deprotonating the alcohol must raise the energy of the starting material and or lower the energy of the transition state Most likely both occur as the negatively charged alkoxide should be less stable than the alcohol but it adds more stabilizing electron density to the transition state 7 Using curved arrows to indicate electron movement suggest a mechanism for the following reaction Be sure to account for relative stereochemistry 1 pt O Me CO2Et 140 oC O CO2Et enantiomer O Me CO2Et H 3 3 O Me CO2Et H O CO2Et The p orbitals that interact to form the new bond must be facing each other Likewise the bond in the cyclopropane ring that breaks must be parallel to the other p orbitals to form cis bonds 4 8 Using curved arrows to indicate electron movement suggest a mechanism for the following two step reaction 1 5 pt OH OMe H3PO4 125 oC O O OMe group stabilizes carbocation intermediate electron rich alkene OMeH OMe O H O H OMe H OH O OMe H OH H O O HMe H MeOH O H HO H O O O 3 3 9 Provide reagents and intermediate products for the following multi step synthesis 2 pt OH steps O OH OH OH K2CO3 Br O heat OH Claisen Rearrangement K2CO3 EtBr O O OsO4 NMO or 1 mCPBA 2 H3O O OH OH KMnO4 can will also oxidize benzylic methyl group so it is not a good choice of oxidant 5 10 Predict the expected max of the following compound Be sure to show your work how did you determine the value 1 pt Base 217 Additional double bonds 60 Auxochromic alkyl groups 35 Exocyclic double bonds 5 Homoannular diene 39 Total 356 nm 11 1 3 Butadiene was reacted with an unknown dienophile to provide a compound with the following spectroscopic data 1H NMR Integration ratio 1 2 1 1 1 3 13C NMR MS ES M at m z 226 Relative percentages of peaks 181 44 1 182 4 9 Based on these spectra suggest a structure for the product of this cycloaddition reaction 2 pt Number of carbons in fragment 100 4 9 44 1 1 1 10 carbons 226 118 45 which corresponds to loss of an ethoxide radical CH3CH2O So total number of C 12 13C NMR shows one ester C O carbon 175 ppm and one alkene peak 125 ppm 1H NMR shows an ethyl ester quartet 2H 4 1 ppm triplet 3H 1 25 ppm Also there is only one alkene peak 5 75 ppm This all suggests a symmetrical molecule with two ethyl esters So it is either one of the following compounds CO2Et CO2Et or CO2Et CO2Et NMR for these two compounds very similar this is it