For each of the pairs shown below, choose the statements that can be used to describe the drawings and their relationship, if a relationship exists.

Transcription

1 I. ( points) ame Page or each of the pairs shown below, choose the statements that can be used to describe the drawings and their relationship, if a relationship exists. (a) (b) and : "Check" any/all descriptions that apply are are are are conformational isomers (conformers) are identical molecules contain at least one R stereocenter (in the pair) represent at least one achiral compound(s) and : "Check" any/all descriptions that apply are are are are conformational isomers (conformers) are identical molecules contain at least one R stereocenter (in the pair) represent at least one achiral compound(s) or each of the compounds shown below: () Identify any sources of stereochemistry by circling the site(s) and providing appropriate stereolabel(s) for each site. If no stereochemistry is present, write "none." () Then choose the statements that can be used to describe that molecule. () Provide information about the expected MR spectra for those compounds specified. (a) (b) (c) The MR spectra for B would show : (write in the number) MR signals The MR spectra for C would show : (write in the number) C MR signals

2 II. ( points) ame Page Carbamic acids are extremely versatile organic compounds widely produced and/or used in organic syntheses. In the following reaction scheme, methylcarbamic acid is deprotonated at its most acidic site under basic (catalytic) conditions. In the second step, a decarboxylation reaction occurs to form the products shown, regenerating the base. Provide the missing information for this two-step reaction. Provide the curved arrow mechanism for the proton transfer. C C methylcarbamic acid Provide the curved arrow mechanism for the second reaction. ΔG to < 0 ΔG to < 0 fast C slow C verall reaction: Keq >> C C regenerated (iii) Circle the sketch of the energy diagram that most accurately represents the reaction scheme shown above.,, and represent the relative energies of the molecules shown in the boxes above ( represents the product mixture). (iv) Sketch the transition state for the second step of this reaction. progress progress progress progress Predict the product(s) formed when molecule undergoes the following treatment. equivalent Molecule 5 (similar to above) undergoes substitution to form. The unusual substitution is explained by considering another major resonance contributor for molecule 5. Provide the curved arrow mechanism for the reaction that produces the ionic compound shown. (iii) Draw the transition state for the one-step substitution. curved arrow mechanism (iii) transition state drawing 5 C

3 III. (8 points) ame Page luticasone propionate (better known as "lonase") is used to treat asthma, allergic rhinitis, and various similar sinus problems. fluticasone propionate Several chiral stereocenters have been indicated with circles and arrows. Label each with an R or an S. S Label with an or a Z the two double bonds indicated with arrows. 0 Provide the requested information for the following reaction, in which is a major product. Draw the starting material C ow many other distinct (i.e. different) products would be expected under these reaction conditions? xplain. S (catalytic) C C C (iii) Molecule has: (please fill in each box with the appropriate number to finish the sentence) enantiomer(s) diastereomer(s) stereoisomer(s) meso stereoisomer(s) (iv) Draw the two chair conformations for and indicate the K eq for your pair of chairs. s always, be sure to clearly and accurately show the axial and equatorial positions for all substituted ring atoms. You do not have to show axial and equatorial hydrogen atoms for unsubstituted ring atoms. (iv) circle one K eq > = <

4 IV. (5 points) ame Page Convert name to structure or structure to name as needed. Be sure to include all information on connectivity and stereochemistry in both your drawings and your naming. nd then fill in the missing information about the MR spectrum for each compound. Draw this compound: (S)-,5,5-triethyl--methylcyclohex--ene ame this compound: Spectra taken on this compound should show: C MR signals MR signals with ratio Compounds containing rings offer interesting insight about conformational stability. Consider molecules and B shown below. C Draw a ewman projection of the C -C bond in as shown; view with the C in front. C Draw a ewman projection of the C -C bond in B as shown; view with the C in front. (iii) Draw a ewman projection for the least stable conformation of the C -C bond in B as shown; view with the C in front. B

5 V. ( points) S (cat.) ame Page 5 The following reactions yield only two different products that share the same molecular formula. These products form in approximately the same concentration, too., showing all information necessary to define the molecule, and describe their relationship by checking the appropriate box. C C ac equivalent C 9 8 C 7 (iii) C Cl Cl ach of the drawings below shows only the connectivity of a molecule or a set of molecules that share this connectivity. or each, check all the statements that can be used to accurately describe this connectivity and the molecule(s) represented by this connectivity. Cl This connectivity represents: "Check" any/all descriptions that apply to this connectivity only unique compound; no stereoisomers exist only enantiomeric compounds only diastereomeric compounds exactly different molecules or more different molecules only optically inactive molecules only optically active molecules This connectivity represents: "Check" any/all descriptions that apply to this connectivity only unique compound; no stereoisomers exist only enantiomeric compounds only diastereomeric compounds exactly different molecules or more different molecules only optically inactive molecules only optically active molecules