NO 2 O NH 2. Br Br. Br CF 3

Transcription

1 1. Rank the following compounds in the trend requested. (15 points each) a. Rank by energy of the lowest unoccupied molecular orbital (LUM). The molecule with the LUM that is lowest in energy is 1, while the compound with the LUM that is highest in energy is b. Rank by rate of S 1 reaction. The compound that will react the fastest in a S 1 reaction is 1, while the compound that reacts the slowest in a S 1 reaction is 5. CF c. Rank by rate of electrophilic aromatic substitution reaction. The compound that reacts the fastest in an electrophilic aromatic substitution reaction is 1, while the compound that reacts the slowest is

2 2. Consider the molecule cytosine shown below which is one of the four main bases found in RA and DA structures. Using the numbering shown, answer the following questions a.(6) What is the hybridization of each nitrogen atom? sp 2 sp 2 sp b.(6) Each nitrogen atom has a lone pair of electrons. Which orbital is each lone pair of electrons held? p sp 2 p c.(4) ow many electrons are conjugated in the cyclic ring? 6 The ring has a large resonance contributor to allow aromatic stability. 2 d.(6) Rank by ability to protonate the lone pair of electrons in acidic conditions. The nitrogen that is easiest to protonate is 1, while the nitrogen that is hardest to protonate is is hardest to protonate as this would make ring nonaromatic and lose aromatic stability. Protonation of 1 would lose resonance stability with lone pair with ring. 2 does not lose any extra stability by protonation and thus is easiest to protonate.

3 3. Consider the molecule 1,3,5-hexatriene. a.(6) Below are shown the six molecular orbitals for the π system of hexatriene. Write a number corresponding to the energy level for each molecular orbital. Write a 1 under the M that is lowest in energy and a 6 under the M that is highest in energy M M M M M M LUM LUM LUM LUM LUM LUM As the number of nodes increases, the energy increases. b.(6) In the space above, circle M under the orbital that corresponds to the highest occupied molecular orbital and LUM under the orbital that corresponds to the lowest unoccupied molecule orbital. There are 6 π electrons, thus M3 is the M and M4 is the LUM. c.(5) Would hexatriene react preferentially in a pericyclic reaction with ethylene or butadiene under thermal conditions? The M and LUM molecular orbitals for ethylene and butadiene are shown. Circle the reaction that would occur thermally.!! LUM LUM M M The M of hexatriene is symmetric, thus the LUM of the reacting pair must also be symmetric for a symmetry allowed reaction. d.(5) What conditions would be required for hexatriene to react in a pericyclic reaction with the other reagent (either ethylene or butadiene which did not react in part c)? eed to change symmetry of M of hexatriene, thus if compound is photolyzed an electron is promoted to change the symmetry of the M.

4 4. Consider the reaction of 3-nitrotoluene with 2 /Fe 3. 2, Fe 3 5-position 4-position a.(6) Draw the arenium ion (sigma complex) that result when the reaction occurs at the 4- position. Include all relevant resonance structures IGEST b.(6) Draw the arenium ion (sigma complex) that result when the reaction occurs at the 5- position. Include all relevant resonance structures c.(5) Circle the resonance form indicated in either part a or part b which is lowest in energy. Resonance form is the only one that places positive charge adjacent to electron donating methyl d.(5) Write the word IGEST under the resonance form in either part a or part b which is highest in energy. Resonance form is the only one that places positive charge adjacent to electron withdrawing nitro e.(4) Should the reaction shown be faster or slower if 4-nitrotoluene was reacted instead of 3- nitrotoluene? Circle the starting material (3-nitrotoluene or 4-nitrotolune) that reacts faster. 3-nitrotoluene 4-nitrotoluene Arenium ion intermediate for 4-nitrotoluene would not place positive charge adjacent to nitro

5 5. Indicate the preferred product for the following reactions. Assume proper work-up for each step. (7 points each) a. KMn 4 a 2 C b. BS, h! c. 1) PhC 3 2) 2 d. 2 2 e. C C f. S B() 2 Pd(PPh 3 ) 4 K 2 C 3 S

6 g. 3, 2 S 4 2 h. 2, Fe 3 i. Cl 2, AlCl 3 Cl j. F a 2 2 k. 1) 2, Fe 3 2) Cl AlCl 3 l. I! I

7 6. Indicate a method to synthesize the products requested in the following examples. You may use any organic or inorganic reagents you desire, but you must begin with the starting material given and synthesize the product requested. More than one step will be required. (15 points each) a. Synthesize paracetamol (also called acetaminophen) starting with phenol? 3 2 S 4 2 Fe, Cl 2 Cl b. Starting with benzene, synthesize the compound shown? Cl 2, Fe AlCl 3 K

8 7. Benzene was reacted as shown in the scheme below. The 1 MR of intermediate A is shown with overlapping peaks between ppm, which in total integrate to 5. The 13 C MR for intermediate B displays 6 peaks at ppm values of 150, 131, 127, 119, 34 and 31. Indicate the structures for compounds A, B and C. Assume proper work-up for each step. (7 points each) AlCl 3 Cl 2 KMn 4 A B C Fe 3 a C 2 A B C