Name Page 1 I 19 points A Aziridines are 3 membered nitrogen heterocycles that can behave as electrophiles in substitution reactions The aziridine 1 shown below has been shown to react with Na OCH3 to give products 2 and 3 Ph Note This abbreviation has been used in the scheme below You may also use this abbreviation when drawing Newman projections on page 5 a The formation of product 3 occurs via i reaction between CH3O and the more substituted carbon of aziridine 1 to generate intermediate 4 ii intramolecular nucleophilic substitution to generate product 3 Provide the structure of intermediate 4 and draw curved arrows showing the movement of electrons in the conversion of intermediate 4 to product 3 OCH3 OCH3 OCH3 N 1 N 2 Na Br 3 N intermediate 3 arrows 2 Na Br Ph N 4 OCH3 Ph N Na Br Ph N 1 Na OCH3 Br draw intermediate 4 and curved arrows for conversion of 4 to 3 5 3 OCH3 b Draw a representation for the transition state structure for the reaction of aziridine 1 with the methoxide anion OCH3 to give intermediate 4 Use dotted lines to symbolize bonds that are forming or breaking draw in nonbonding electrons and indicate partial charges when if applicable You do not need to show the sodium cation transition state structure for conversion of 1 to 4 2 if incorrect partial charges Ph N Br OCH3 4 c The product 3 above will be formed as check one X a single achiral compound a single chiral compound a mixture of enantiomers a mixture of diastereomers 2 B A number of biologically active natural products contain tetrahydropyran subunits i e a six membered ring containing an oxygen atom Molecule 5 is a potentially useful precursor to many of these natural products Draw the lowest energy chair conformation of molecule 5 Clearly indicate the directionality for all of the H and non H substituents that are drawn on the structure below You do not need to illustrate the position of nonbonding electrons H OCH3 H H3C H H3CH2C H O H Molecule 5 CH3 CH2CH3 H3CO H H H H H CH2CH3 O CH3 CH2CH3 CH3 chair shape 2 connectivity 2 stereochemistry 2 lowest energy conformation 2 lowest energy chair form of molecule A 8 Page 2 II 27 points A The molecule shown below is a member of the chlorosulfolipid class of natural products and was isolated from a toxic Adriatic mussel This molecule is believed to be one of the agents responsible for Diarrhetic Shellfish Poisioning Assign the stereochemical configuration of the selected tetrahedral carbon stereocenters R or S and the alkene E or Z that are indicated by the arrows note that you do not have to assign the configuration of every stereocenter in the molecule If R S or E Z labels are not applicable because a carbon indicated by an arrow is not a stereocenter or the alkene cannot be assigned as E or Z then put an X through both R and S or E and Z Name R S Cl H R S Cl H SO3 H O Cl H Cl H Cl H E Z Cl R S 3 for each incorrect answer B For each of the following individual molecules check all the descriptions that apply no partial credit a b c OCH3 F H 12 HO CH3 CH3 CH3 O no partial 5 H3C H3C Molecule 5 X is not optically active has an enantiomer has at least one chiral diastereomer contains at least one R stereocenter has an achiral meso diastereomer F H3C Molecule 6 X F 6 CH3 no partial is not optically active has an enantiomer has at least one chiral diastereomer contains at least one R stereocenter has an achiral meso diastereomer X X X 3 C Using lines dashes and wedges to indicate stereochemistry if when appropriate draw the structure of 2E 4Z 5 bromohepta 2 4 diene X 3 3 H3C X X 7 Molecule 7 O no partial is not optically active has an enantiomer has at least one chiral diastereomer contains at least one R stereocenter has an achiral meso diastereomer Br 2 points per error 6 Page 3 III 23 points Enolates the conjugate bases of ketones are useful nucleophiles in a variety of carbon carbon bond forming reactions One method that is commonly used to generate enolates is to simply deprotonate ketones with a base For example the reaction between 2 methylcyclohexanone and a base leads to the formation of a mixture of two enolate regioisomers 8 and 9 The ratio of 8 and 9 depends on the type of base that is used Name O H H H CH3 Li B 2 methylcyclohexanone SM O H Li CH3 HB O Li CH3 HB H H 8 9 Note B is a generic base and HB is its conjugate acid Specific bases are given in parts b and c below a Based on the information provided below construct an energy diagram for the conversion of 2 methylcyclohexanone base SM to products 8 and 9 On your diagram clearly show the position of products 8 and 9 transition states A and B and draw the appropriate energy curves The reaction occurs in a single step No intermediates are formed The conversion of SM to 8 proceeds through transition state A The conversion of SM to 9 proceeds through transition state B kcal mol G A B 2 kcal mol G for SM G for SM G EA SM G EA SM 8 2 kcal mol 9 4 kcal mol A 4 kcal mol B 8 kcal mol SM Progress of Reaction 8 9 10 b When Li N CH CH3 2 2 is used as a base the product ratio is controlled by reaction kinetics Which is the major product under these conditions circle one answer c When Li OC CH3 3 is used as a base the product ratio is controlled by reaction thermodynamics Which is the major product under these conditions circle one answer 2 d When enolate 8 is treated with chlorotrimethylsilane molecule 10 shown below is formed How many signals peaks will appear in the NMR spectra of molecule 10 put numbers in the boxes cannot be answered using only the information given cannot be answered using only the information given 2 A B A B 8 9 8 9 CH3 Si O H3C H3C 38 6 3 13C NMR signals identifying chemically distinct carbon atoms 1H NMR signals identifying chemically distinct H atoms with ratios of provide numbers in the boxes 9 2 2 2 2 3 note the order of numbers in your ratio is not important CH3 Molecule 10 3 Page 4 IV 28 points A For each of the pairs of molecules drawn below place letters in the corner boxes corresponding to all accurate descriptions of the relationship between the two molecules a Name all letters that apply B F G H no partial 3 all letters that apply B F G I no partial 3 A enantiomers B diastereomers C different conformations of the same molecule D identical conformations of the …