b.(12) Where is pyrrole protonated under strong acidic conditions? Why this site of protonation?

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1 1. Rank the following compounds in the trend requested. (15 points each) a. Rank the following dienes by rate of Diels-Alder reaction. The diene which reacts the fastest with an alkene is 1, while the diene which reacts the slowest is b. Rank by UV-Vis absorbance. The compound with the highest wavelength absorbance maximum is 1, while the compound with the lowest wavelength absorbance maximum is c. Rank by rate of electrophilic aromatic reaction. The compound which will react the fastest with an electrophile is 1, while the compound which reacts the slowest is 5. a

2 2. Unlike imidazole, which is a modest ønsted base, pyrrole needs very strong acidic conditions to become protonated. Under these conditions pyrrole is also preferentially protonated on a different type of atom than what occurs with imidazole. imidazole pyrrole a.(8) Why the difference in basicity for imidazole and pyrrole? Imidazole can protonate a lone pair of electrons on one of the nitrogen atoms and still maintain an aromatic system. If pyrrole protonates the lone pair of electrons on nitrogen it will lose the aromatic stabilization. b.(12) Where is pyrrole protonated under strong acidic conditions? Why this site of protonation? Pyrrole is protonated on the C2 carbon position. Protonation at this position yields the most stable arenium ion. 3.(10) 2,4-dinitrofluorobenzene is called Sanger reagent and is used to determine protein structures. Show the structure of the product obtained when Sanger reagent is reacted with the methyl ester of phenylalanine. 2 C 3 methyl ester of phenylalanine 2 F 2 C C 3 2 a nucleophilic aromatic substitution

3 4. When naphthalene is reacted in an electrophilic aromatic substitution the electrophile preferentially adds to the 1-position E+ major product a.(12) Draw the resonance structures of the arenium ion intermediate for this naphthalene reaction. Indicate which resonance structures maintain some aromatic character. The arenium ion formed by reaction of the electrophile at the 1-position generates five resonance structures. The first two shown maintain an aromatic ring. Reaction at the 2-position only has one resonance structure which maintains an aromatic ring. E E E E E E E b.(8) aphthalene, like benzene, is aromatic and can be represented by three resonance structures as shown. Unlike benzene, all the bonds in naphthalene are not the same length. Which bond, A or B in the structure shown below, is longer? Why? A B Bond B is longer than bond A. As seen in the resonance structures in two of the three resonance forms (which are equal in energy) there is a single bond for bond B, therefore more single bond character in this bond. c.(14) Knowing the information given in part a, what are the preferred products for the following reactions? C 3 2, Fe 3 C 3 2, Fe 3 goes to 1-position of more activated ring in both cases

4 5. Indicate the preferred product in the following reactions. nly write one product in each case with proper regio- and stereoprefence where relevant. (7 points each) a. +, C 3 C 3 b. 1) 2, 2 2) triethylamine c. C C 1 equiv. d. C C e. C C f. C 3 C 3 1 equiv.

5 g. 3, 2 S 4 2 h. 2, Fe 3 i. C 3 Cl, AlCl 3 j. Cl AlCl 3 k. C 3 a, 3 (l), C 3 C 3 l. C Cl C 3 a C C 3 m. 2 S 4

6 6. Starting with toluene, show how to synthesize the following compounds. In reactions that display ortho/para preference, assume the para product is the major product. You may use any reagents you desire but you must use toluene as the starting material. (15 points each) a. C 2 toluene 2 B C 2 r2, Fe 3 KMn 4 3, 2 S 4 C 2 2 b. Cl B r2, Fe K AlCl 3 7.(20) Compound A with molecular formula C was reacted with isobutylene and sulfuric acid to create product B. The 1 MR of both A and B are shown below with the relative integrals of the peaks indicated. Both A and B show a broad peak around 3300 cm -1 in the IR. What are the structures of A and B? A 2 S 4 B 3 C 3 C 1 MR of A indicates an aromatic compound with para substitution. IR indicates an alcohol - only way C fits data is compound indicated. Reaction is a Friedel-Crafts alkylation which places two t-butyl groups ortho to hydroxy group to form product.