(a) Draw a circle around the longest C-C bond(s) in serotonin. sp 2. sp 3

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Cecil Sherman
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1 I. ( points) ame Page A. Serotonin is an important neurotransmitter that is thought to play an essential role in the regulation of moods, despite being concentrated in the enterochromaffin cells in the intestines. atom atom serotonin atom (a) Draw a circle around the longest - bond(s) in serotonin. (b) Draw a rectangle around the best hydrogen bond donor group in serotonin. (c) 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). Be careful to consider appropriate bond angles in small rings. atom atom atom all three answers must be right for the row = hybridization electronic geometry observable geometry sp sp sp bent no partial trigonal pyramid Molecule is a metabolite of serotonin. There are two acidic protons in this compound, with pkas of ~ and ~9.5. (a) Is this the form of Molecule that you would expect to exist in the acidic (p ~) environment of the gut? Please explain (be specific) in your answer., the carboxylic acid group would be mostly deprotonated (b) At a p of 9., two species of exist in an aqueous solution, but one is observed at a higher concentration than the other. Draw the forms in the appropriate boxes. pts if correct structures but switched. 0 points if the structures are wrong > greater than (c)the following structures are related to Molecule shown above. For each structure, circle the best description of the relationship (i) (ii) (iii) (iv) a resonance form of a resonance form of a resonance form of a resonance form of a conjugate acid of a conjugate acid of a conjugate acid of a conjugate acid of a conjugate base of a conjugate base of a conjugate base of a conjugate base of a structural isomer of a structural isomer of a structural isomer of a structural isomer of

2 II. (9 points) A. ame Page (a) Diazomethanone is a neutral molecule that is best represented by a set of resonance contributors, each containing formally charged atoms. The connectivity of diazomethane is shown; draw all the closed shell resonance contributors that can be used to represent this compound. ote: formal charges on atoms must be +, 0, or -. closed shell resonance contributors for diazomethanone diazomethanone connectivity only points each structure 6 (b) ircle the resonance contributor that you think best contributes to the overall structure of this compound. (c) A structural isomer of diazomethanone,, can be drawn that: - contains only closed shell, uncharged atoms - contains a ring - contains no sp hybridized atoms Draw a complete Lewis structure for this isomer (d) A structural isomer of diazomethanone,, can also be drawn that: - contains only closed shell, uncharged atoms - contains no ring Draw a complete Lewis structure for this isomer Despite its bad reputation, arsenic can be found in a wide variety of organic compounds. ne of these is shown. Arsenic behaves just like its column mates, and P, in organic compounds. As Arsine is toxic gas that has also found use in the production of semiconductors Provide the missing information for the following proton transfer reaction. ways draw the most significant resonance contributor when more than one is possible. Be sure to balance your reactions. not the best resonance - 0pts (a) K eq = 0 - As As + + a a (b) what is the pka for arsine? pts blue structure (best resonance) pt spectator ~6 (5-6 = -)

3 A. III. (0 points) ame Page (a) Bufotenin is a toxin that is excreted through the skin of some poisonous toads. Draw the single best resonance contributor for citrinin (all atoms closed shell, all atomic formal charges of +, 0, or -. is also fine Bufotenin - one resonance form (b) Bufotenin is a Bronsted acid whose most acidic proton has a pka of ~8.5. ircle the bases in the box that can deprotonate bufotenin with a K eq > 0. Li l l l K K a 6 Bufothionine is another poison isolated from the skin of some toads. bond bond 5 S bond bond bond (a) Place Bonds -5 in order from shortest to longest, as predicted by considering resonance, hybridization, etc. If any bonds are predicted to be the same length, circle them. shortest 5.5 bond order and hybrid for - rd longest (b) The most acidic site on bufothionine has a pka of ~ -. Predict the Keq for the reaction between bufotionine and af. bufothionine Keq = 0 6. atom (c) 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). Be careful to consider appropriate bond angles in small rings. all three answers must be right for the row = no partial hybridization electronic geometry observable geometry S atom atom atom atom atom sp sp sp bent bufothionine

4 IV. ( points) ame Page (a) Methyl--cyanoacrylate, better known as "Super Glue," has found many useful applications, especially in forensic science. Super Glue has such strong adhesive properties because it polymerizes in the presence of any attacking ions, for instance hydroxide, as shown below. Provide the missing information for each step in this synthesis. Remember to use the curved arrow notation accurately and efficiently. Draw the curved arrow mechanism for the formation of the final product methyl--cyanoacrylate polymerization continues, leading to strong adhesion properties bservation: adhesion is significantly reduced if water is present. Explain this briefly by considering how water might react with the product shown. protons would react with the anion preventing further polymerization, no more basic sites can form. (b) i) Assess bond angles and geometries for the atoms indicated in methyl--cyanoacrylate. VSEPR geom. for hybridization for sp bs. geom. for one bs. geom. for methyl--cyanoacrylate most significant contributor ii)draw the best other (different from the one shown) significant resonance contributor for this compound; make sure all atoms are closed shell, and atomic formal charges are +, 0, or -. all electrons and charges must be shown, no partial credit (c) Provide an accurate and complete three-dimensional orbital picture for the most significant resonance contributor for this fragment of methyl--cyanoacrylate. 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. l bond angles should reflect the appropriate geometry and hybridization chosen for your drawing. points per atom - geometry must be correct bond angle must be accurate p orbital must be consistent with hybrid plane best contributor 8

5 V. (6 points) ame Page 5 (a) Both l and l can act as strong Lewis acids, but the following reaction gives some indication of their relative strengths. Provide the curved arrow mechanism for the complexation reaction l l l l l l l Draw the complex that forms, and provide the curved arrow mechanism for the decomplexation that occurs to give the products shown l l l l l l l pts complex (with charges) pts for curved arrow l l l l l l l (b) izarin, also known as Turkey Red, is a p sensitive dye isolated from the roots of madder (Rubiciaceae) plants. It has been used as a dye for over,000 years. izarin reacts with l to form the complex shown below. Another all-closed shell resonance contributor can be drawn for this particular complex, with the positive charge delocalized to another (different) oxygen atom. Draw this contributor. l l l (c) The resonance contributor you drew above should offer some valuable information about the relative acidity of each of the - groups. Provide the missing product(s) and balance your reaction. Li pt per product, correct must be chosen Li equivalent (d) The "enol" functional group plays an important role in the resonance for alizarin and other compounds. Draw a simple D orbital picture of this enol (the major resonance form shown). You should use lines, dashes, wedges, p orbitals (lone or overlapping) to show the direction of all electrons (or empty orbitals) in your drawing. l bond angles should reflect the appropriate geometry and hybridization chosen for your drawing. enol point per atom - geometry must be correct bond angle must be accurate p orbital must be consistent with hybrid plane point for pi bond point for p orbital with lone pair on 5

1.5 h; 100 points please print clearly Dr. Kathleen Nolta Signature UM ID # Problem Points Score GSI I 24 II 19 III 20 IV 21 V 16 Total 100

1.5 h; 100 points please print clearly Dr. Kathleen Nolta Signature UM ID # Problem Points Score GSI I 24 II 19 III 20 IV 21 V 16 Total 100 hemistry 0 First ame First Examination Last ame.5 h; 00 points please print clearly Dr. Kathleen olta ignature UM ID # PRIT TE FIRT LETTER F YUR LAT AME ERE: Problem Points core GI I 4 II 9 III 0 IV V