ame I. ( points) Page 1 A. The compound shown below is a commonly prescribed antifungal drug. It belongs to a category of compounds known as triazoles. Analyze the geometry and other properties for various atoms in this drug. (i) Total p electrons in ring atom 1 atom (ii) Total p electrons in ring or each of the atoms indicated with an arrow, provide the atom's most reasonable hybridization as well as its electronic geometry (VEPR) and observable geometry (write none if it is not observable). all three answers must be right for the row = no partial hybridization (iii) Total p electrons in ring 1 (a) ind all tetrahedral chiral centers in this compound and give them appropriate stereolabels two of these both (b) or all the rings indicated, count the number of electrons held in p orbitals for all ring atoms. (c) ow many aromatic rings are in this molecule? (d) Put a box around the shortest - bond in this molecule. electronic geometry observable geometry. a triazole ring atom 1 atom atom 1 atom sp sp sp sp trigonal planar tetrahedral (Td) tetrahedral (Td) trigonal planar Provide an accurate and complete three-dimensional orbital picture for this triazole ring (considering all valid resonance contributors when you assess hybridization for each atom). You should use lines, dashes, wedges, and p orbitals (lone or overlapping) to show the direction of all electrons (or empty orbitals) in your drawing. how all bonds and all bond angles should reflect the appropriate geometry and hybridization chosen for your drawing. points per atom - geometry must be correct bent bent trigonal pyramid The triazole ring is shown below. Draw a complete set of all closed shell resonance contributors for this molecule; atomic formal charges should be +1, 0, or -1. Then circle the best of the ones you have drawn. bent pts each, -1 for missing circle - either or both contributors with only s charged is good 8 bond angles must be accurate must show pi bonds connected hybrid system must be consistent with p orbital here all p orbitals are in depth 1
II. ( points) ame Page A. A sulfur-chlorine bond reacts in addition reactions like mixed halogens; the sulfur atom is the electrophilic site and it forms a halonium-like cyclic intermediate. how the curved arrow mechanism for the formation of this intermediate. Though stereoisomers form, you should draw only one intermediate and the final product formed from this intermediate, showing stereochemistry clearly. (a) (b) R (c) curved arrow mechanism for the formation of the intermediate one high energy intermediate, showing stereochemistry clearly (b) account for all carbons ) 1pt ) Zn 1pt 1pt 1pt. This transformation combines complexation, electrophilic aromatic substitution and rearrangement! It starts with a complexation reaction, which generates a leaving group and an electrophilic. The pi bond in the smaller ring nucleophilically attacks the electrophilic carbon, forming a new -atom ring and a carbocation resonance-stabilized by the adjacent nitrogen. A ring expansion generates a new carbocation and in step, a final proton transfer returns the ring's aromaticity (you may use a generic : the final product that results from the intermediate you drew in (a). Predict the main organic products (not byproducts) of these multi-step transformations; if stereoisomers form, draw one and write "+ enantiomer" or "+ diastereomer" in the box. no new stereo - just triple to double (a) (c) balance your reaction 1) 1) a a Pd-a ) E 1pt only Pb ) if a/ organic pts is correct points per intermediate (either resonance) points per mechanistic step grading stops with irrational step 17
III. ( points) ame Page A. Each of the following transformations demonstrates some form of selectivity. Provide the other information requested. (a) (i) Draw the starting (ii) Draw a ewman projection for the most stable material conformation of the bond highlighted in the product. Use the view indicated and consider sterics only. view (b) only this stereo first must be correct connectivity and stereo then for conformation electivity in proton transfers occurs by choosing your reagent wisely. The most acidic proton in compound A has a pka ~., while the second has a pka ~10.. If treated with an excess of the following bases, which will result in a zwitterionic form of compound A (removing most of the first proton, while leaving the second relatively untouched). compound A K 10. K 17 Li a Li 9 a K 1 (c) (i) Draw the product 1) 1) Li ) (ii) Draw the product ) a only this stereochem only this stereochem or each of the following connectivity drawings check all the descriptions that apply. (a) (b) (c) This connectivity represents 1 unique molecule a diastereomeric pair an enantiomeric pair or more stereoisomeric molecules only chiral molecules only achiral molecules This connectivity represents 1 unique molecule a diastereomeric pair an enantiomeric pair or more stereoisomeric molecules only chiral molecules This connectivity represents 1 unique molecule a diastereomeric pair an enantiomeric pair only chiral molecules only achiral molecules only achiral molecules or more stereoisomeric molecules
IV. ( points) ame Page In each of the following reactions more than one product is formed. Draw each product; be sure to show all structural and stereochemical properties unambiguously. When regioselection is predicted, draw only major regioisomers. ote that sometimes you are given extra guidance about where to put your product(s). Also, provide the MR information requested and analyze your products, depending on the problem. A. The MR spectra for would show : (write in the number) (cat.) 1 MR signals pts each These products are (check all that apply): Which of these products is/are optically active? (check one) enantiomers diastereomers structural isomers ne oth either These are the same (meso) either one may be drawn but not both 1 MR signals Pd/ pts each. 1) ) pts each These products are (check all that apply): Which of these products is/are optically active? (check one) enantiomers diastereomers structural isomers ne oth either D. The MR spectra for D would show : (write in the number) 1 MR signals 1 MR signals D (cat.) Draw major product(s) cis note this becomes cis/trans with the addition both must be drawn - they are different pts each - must draw top D now too E. pts each These products are (check all that apply): Which of these products is/are optically active? (check one) enantiomers diastereomers structural isomers ne oth either
Energy, G V. ( points) A. ame Page The chemical transformation shown below consists of some very familiar hemistry 10 reactions. Provide the missing details for this multi-step process. e sure to read the specific prompts carefully - sometimes curved arrow mechanisms are requested, and sometimes transition state drawings or intermediates are requested. (a) Provide the curved arrow mechanism - step 1 tarting material (b) Provide the curved arrow mechanism - step (c) Provide a drawing of the transition state ts (d) Provide the curved arrow mechanism - step Product pts each -1 for any other (g) Assign stereolabels to all circles chiral centers in the product, P 10 onsider the energy diagram below, which might be used to illustrate the reaction above. (a) Using positional labels, state how you would calculate the following (give your answer as a mathematical equation, like " minus Y") (f) Draw the intermediate and the curved arrow mechanism for the last step (e) Provide a drawing of the transition state ts b d f h (i) the E a (ΔG ts ) of the rate determining step for the reverse transformation? h minus P (ii) the ΔG for the second step in the reverse transformation? e minus g c e g (iii) the E a (ΔG ts ) of the second step for the formation of P from M? d minus c M P (b) In this diagram, what positional label(s) represent(s) the drawing you provided in box c of part A above? d reaction coordinate (c) In this diagram, using positional labels, what represents the drawing you provided in box f of part A above? g
VI. (9 points) ame Page A. or each of the following molecules, choose all the descriptions that apply; write the letters corresponding to those descriptions in the box with the drawing you are analyzing. (a) (b) (c) (d) a: a A,, D A) has an enantiomer ) has an achiral diastereomer ) has a chiral diastereomer D) is optically active E) is meso ) contains an R stereocenter (a)if you remember your second midterm, you might recall that you were asked to evaluate chair conformations for molecules like (and including) this one. Draw all the biomolecular elimination products that would result from this starting material. Then consider the effects of the changes suggested. M b: b a c: c A,, D, d: d (E) pts each (b) Draw the chair conformation that is preferred for the E reaction shown above. As 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. Must be correct molecule and axial If M is changed to (i) a b a and b are:, the rate of the E reaction is expected to (check one) (ii) increase decrease c d c and d are: A, D, (iii) the number of products is expected to (check one) increase decrease be unaffected be unaffected (c) or each of the following pairs, choose all the descriptions that apply; write the letters corresponding to those descriptions in the box with the drawings you are analyzing. meso not meso e f If M is changed to (E) c and d are: A,E, (E) A) different molecules ) structural isomers ) conformers D) diastereomers E) enantiomers ) represent at least one optically active molecule