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U of M CHEM 210 - Key 1

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I. (42 points)hybridization electronic geometry observable geometryatom O1atom N122Name _______________________Page 1sp2trigonal planarbentbentall three answers must be right for the row = 2 no partialatom N22sp2trigonal planaratom O22sp3tetrahedral (Td)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.For each of the atoms indicated with an arrow, provide the atom's most reasonable hybridization as well as its electronic geometry (VSEPR) and observable geometry (write none if it is not observable).N2N1B.C.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. Show all bonds and all bond angles should reflect the appropriate geometry and hybridization chosen for your drawing.2 points per atom - geometry must be correct bond angles must be accuratemust show pi bonds connectedhybrid system must be consistent with p orbitalhere all p orbitals are in depth12O(S)(S)O(S)(S)NNN(Z)(Z)O N Ntrigonal pyramidatom O2atom O1sp3tetrahedral (Td)bentA.(a) Find all tetrahedral chiral centers in this compound and give them appropriate stereolabels(b) For all the rings indicated, count the number of electrons held in p orbitals for all ring atoms.(i) Total p electrons in ring662(c) How many aromatic rings are in this molecule?3462(d) Put a box around the shortest C-O bond in this molecule.2two of these both SNCNCNH3Ca triazole ringNCNCNCHHHHHHH(ii) Total p electrons in ring(iii) Total p electrons in ringNCNCNH3CHHThe 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.NCNCNH3CHHNCNCNH3CHHNCNCNH3CHH82 pts each, -1 for missing circle - either or both contributors with only Ns charged is goodName _______________________Page 2II. (35 points)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. Show 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.C.This transformation combines complexation, electrophilic aromatic substitution and rearrangement! It starts with a complexation reaction, which generates a leaving group and an electrophilic C. The pi bond in the smaller ring nucleophilically attacks the electrophilic carbon, forming a new 5-atom ring and a carbocation resonance-stabilized by the adjacent nitrogen. A ring expansion generates a new carbocation and in step 4, a final proton transfer returns the ring's aromaticity (you may use a generic :B.BF3NHOHNHBNHNHHBNHOHFFFNHOHBFFFNHBF3OHHBNHBF3OHHB3 points per intermediate (either resonance)2 points per mechanistic stepgrading stops with irrational step17SClSClClSone high energy intermediate, showing stereochemistry clearlythe final product that results from the intermediate you drew in (a).(a)(b)SORClSNaH1)2)CH3BrNa/NH33)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.H2Pd-CaCO3PbOB.(b) account for all carbons(c) balance your reaction333curved arrow mechanism for the formation of the intermediate32(c)1)2) O33) ZnO2OOOOONaBrH2E1pt only if organic is correct2 pts1pt1pt(a)1pt4no new stereo - just triple to double1ptOOOName _______________________Page 3III. (36 points)Each of the following transformations demonstrates some form of selectivity. Provide the other information requested.BrHBrB.(R)(R)OHHH3C BrBrHA.(ii) Draw a Newman projection for the most stable conformation of the bond highlighted in the product. Use the view indicated and consider sterics only.CNH3NCl SOOCH3(i) Draw the starting materialfirst 3 must be correct connectivity and stereothen 3 for conformation6(a)(b)(ii) Draw the product4(c)a diastereomeric pairan enantiomeric paironly chiral molecules1 unique moleculeXX3 or more stereoisomeric moleculesThis connectivity representsonly achiral moleculesa diastereomeric pairan enantiomeric paironly chiral molecules1 unique moleculeXX3 or more stereoisomeric moleculesThis connectivity representsonly achiral moleculesa diastereomeric pairan enantiomeric paironly chiral molecules1 unique moleculeX3 or more stereoisomeric moleculesThis connectivity representsonly achiral moleculesFor each of the following connectivity drawings check all the descriptions that apply.(a) (b)(c)444Br2only this stereo4viewO OHHOSelectivity in proton transfers occurs by choosing your reagent wisely. The most acidic proton in compound A has a pKa ~3.5, 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).ClClOOOKKO ONHNaLiHcompound ANaOLiOH3CNHK915355361710.56N1)2)NaN3(S)(S)N3LiH1)2)(R)(R)OCl(i) Draw the product4BrOBrBrno partial creditonly this stereochemonly this stereochemno partial creditno partial creditName _______________________Page 4IV. (46 points)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. Note that sometimes you are given extra guidance about where to put your product(s). Also, provide the NMR information requested and analyze your products, depending on the problem.C.B.H2O13C NMR signals1H NMR signalsThe NMR spectra for B would show :(write in the number)254BD.13C NMR signals1H NMR signalsThe NMR spectra for D would show :(write in the number)245DCH3OOHNO3One Both NeitherWhich of these products is/are optically active? (check one)Xenantiomersdiastereomersstructural isomersThese products are (check all that apply):X622A.6One Both NeitherWhich of these products is/are optically active? (check one)Xenantiomersdiastereomersstructural


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