C sp2 trigonal planar trigonal planar 3

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1 I. ( points) ame Page A. Rocuronium bromide (Zemuron) is a muscle relaxant that is used in the application of anesthesia. It is used most often to facilitate endotracheal intubation because of its powerful neuromuscular blocking effect. (a) Label the indicated chiral stereocenters with the appropriate stereochemical designation. pts/label + - (b) For each of the atoms indicated with an arrow, provide the atom's most reasonable hybridization as well as its electronic (VSEPR) geometry, and its observable geometry (shape). Atom ybridization sp sp sp Electronic (VSEPR) geom. tetrahedral bs. geom (shape) sp trigonal planar trigonal planar tetrahedral trigonal planar trigonal pyramid bent bent. Each of the following transformations yields one major organic product (i.e., no mixtures of stereoisomers or regioisomers). Draw this product for each (do not worry about byproducts, focus on the product that is being synthesized). Please pay close attention to the direction of each arrow. ) /Fe ) ) S (cat.) ) S a S (cat.)

2 II. ( points) ame Page A. For 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 "E." () Then choose the statements (A-F) that can be used to describe that molecule and write the letters in the box under each molecule. If no descriptions apply, write "E" in the smaller box. E A) is a meso compound ) has at least one chiral diastereomer ) has an enantiomer D) has at least one achiral diastereomer E) has a meso stereoisomer F) would show < -MR signals. For each of the following pairs, choose all the descriptions (A-G) that apply; write the letters corresponding to those descriptions in the box with the pair of drawings. and : F D E A F and 6: G (Z) 6 A) are enantiomers ) are diastereomers ) are structural isomers D) are conformational isomers (conformers) E) are identical molecules F) contain at least one R stereocenter (in the pair) G) represent at least one achiral compound pts for the label(s) pt each if there are labels pts (no partial) for descriptions 7 7 and 8: F G and :. Translate the molecular structure to a name and the name to a molecular structure (include stereochemistry): and 0: D A F Z E F 0 (i) - pts/error, numbering is one error (ii) --chloro--methylcyclobut--ene --bromohept--yne can be drawn many ways, check stereochem

3 III. (0 points) ame Page A. The following rearrangment reaction yields an isocyanate product that is useful in organic syntheses. It begins with a proton transfer, then a rearrangement step completes the transformation. Provide the missing information in each box. (ii)the product of this first step is best shown as a set of two resonance contributors, each containing only one charged atom: draw them. (i) Provide the curved arrow mechanism second blue arrow may be replaced with two red arrows proton transfer (iii) Using the EST resonance contributor, show the curvedarrow mechanism for the formation of product set shown below. (iv) Draw the other major resonance contributors for the isocyanate product pts each for the resonance contributor points for the mechanism - pts if the wrong resonance contributor is used the right resonance contributor is better + 0 isocyanate product (v) Assuming the hybridization model for all atoms (considering all resonance contributors) provide an accurate and complete three-dimensional orbital picture for the best overall resonance contributor for the isocyanate product, using lines, dashes, wedges, and p orbitals (lone or overlapping) to show the direction of all electrons (or empty orbitals) in your drawing. All bond angles should reflect the appropriate geometry and hybridization chosen for your drawing. pts each atom (- both as ) geom must be correct/linear. The following energy diagram reveals the energy changes that occur during a specific reaction when formation of one carbocation leads to two possible rearrangements, eventually leading to structurally isomeric products. Answer the questions about the diagram. e sure to show the sign of all energy changes. Energy A (i)what step is the ratedetermining step in the to A Step or I to (reverse) transformation? D E Reaction Progress I J F G kcal/mol (ii) Which product would be favored if the reaction were run reversibly, under thermodynamic conditions? (iii) List the points that represent transition states in this diagram. (iv) Estimate the ΔG for the step with the smallest k r in the A to (forward) transformation. (v) What is the ΔG for the ratedetermining step for the complete A to G (forward) transformation?, D,, J, F +6 kcal/mol + kcal/mol

4 IV. ( points) A. Provide the missing information. (i) note the rings are different ame Page (iii) Using a ewman projection, draw the most stable conformation for the - bond; should be in front. / only this stereochemistry (ii) alone forms: with its enantiomer circle one with its diastereomer - if wrong molecule - if wrong conformer When Molecule is treated with a bulky base, a bimolecular elimination process yields alkene product(s). Draw all products expected to form. (iv) DU E. The following addition reaction yields a variety of structurally isomeric products sharing the formula 8 6. Draw the other products (,, and ), given the information provided. onnectivity alone (no stereochemistry) should be considered in your drawings. after a single rearrangement (i) without rearrangement (ii) -MR: 8 signals (iii) -MR: 6 signals stereoisomeric mix stereoisomeric mix single achiral molecule S (cat.) only this stereochem 6 (iv) Draw the most straightforward curved arrow mechanism for the formation of 6 from, using and + as needed. This transformation requires two rearrangement steps. Ignore stereochemistry. pts per step (all arrows must be correct) pts per intermediate (charges, too) Grading stops with first illogical step 6 8

5 V. ( points) ame Page A. Molecule undergoes bimolecular elimination to yield a single alkene product. Provide a drawing for the conformation of that undergoes this elimination. As always, be sure to show both axial and equatorial positions for all substituted ring atoms. Draw bond angles carefully, and show connectivity and stereochemistry clearly. (i) hair conformation that undergoes E (ii) alkene product - pts per error (bond angles, missing, etc.) points if correct chair (connectivity + stereochem) then points for the right conformation 6 The results of the above reaction might change if Molecule is used as the starting material instead of Molecule. Answer the questions to show if (and how) anything might change. (iii) Molecule and Molecule are: circle one enantiomers diastereomers structural isomers unrelated compounds (iv) Molecule will yield circle one a larger a smaller the same (v) Molecule will react circle one more slowly than faster than at the same rate as number of E products as Molecule Molecule. Each of the following reactions yields two major products that share the same molecular formula. Draw these products, showing all stereochemistry (if any) clearly, and define their relationship. no credit if drawings are incorrect (i) ) 9- ) /a s may be drawn in and are: (circle one) enantiomers diastereomers structural isomers (ii) 6 no credit if drawings are incorrect and 6 are: (circle one) (excess) Pd/ enantiomers diastereomers structural isomers 6 6

6 VI. (0 points) A. Draw a circle around the compounds which are aromatic or contain at least one aromatic ring. ame Page 6 no partial. The Pictet-Spengler Reaction involves an interesting twist on EAS reactions. When the starting material is placed in an acidic environment, a proton transfer generates the strong electrophile required for EAS. Provide the most straightforward three-step curved arrow mechanism that leads to the product shown; the acid used to generate the electrophile is regenerated. You may use - and - for any proton transfer step. R mechanistic arrows should reflect the contributor drawn R must pick the right for complexation intermediate pts pts per step (all curved arrows) pts per intermediate +. omplete the following by providing the missing information. If any product forms as a stereoisomeric mixture, please draw one structure showing stereochemistry clearly and write "+ enantiomer" or "+ diastereomer" in the box. When providing reagents, be sure to number steps and draw all appropriately. (i) equivalents ) a/ or Pd/aS Pb ) ) Zn no partial for reagents - if missing numbers R Mn ) Pd/aS Pb ) ) ) /a/ - for adding + enantiomer or + diastereomer when not needed or both dashed - for + enantiomer + enantiomer no partial for reagents - if missing numbers - for + enantiomer S or Al or Fe, etc ) / S (cat.) ) Fe