Coursehero >> Texas >> U. Houston >> CHEM 6353

Course Hero has millions of student submitted documents similar to the one below including study guides, homework solutions, papers, exam answer keys and textbook solutions.

CHEM 1 6353 MIDTERM II: CATIONS, ANIONS, RADICALS, PERICYCLIC REACTIONS Given in class period on 10/29/2008 Name:_________________________________________ UH Student ID#:_______________________________ Question 1:____/50 Question 2:____/60 Question 3:____/20 Question 4:____/30 Question 5:____/40 Total:_________/200 This exam should have eight (8) pages. If it does not, ask Ognjen for a replacement immediately. CHEM 6353: PHYSICAL ORGANIC CHEMISTRY Fall 2008 (August 25th December 6th 2008) 2 Question 1 50 points Compound 1, labeled with 13C as shown (*), has been proposed to rearrange to its isomer 1 through transient intermediate diradical 2. The activation enthalpy ( H ) for this reaction is 29 kcal mol 1. The heat of formation of 1 is +129 kcal mol 1. The bond dissociation energy of H2 is 104 kcal mol 1, and the C H bond dissociation energy in benzene is 112 kcal mol 1. The heat of formation of benzene is +20 kcal mol 1. Calculate H for the ring opening step k 1. State any assumptions you need to make in order to do this calculation. CHEM 6353: PHYSICAL ORGANIC CHEMISTRY Fall 2008 (August 25th December 6th 2008) 3 Question 2 60 points (20 + 20 + 20) Provide reasonable mechanisms for the following reactions and account for the stereochemistry of the product, where applicable. Clearly label each step in as much detail as possible (e.g. thermally allowed [ 4s + 4a] cycloaddition). Me D D Me D D CHEM 6353: PHYSICAL ORGANIC CHEMISTRY Fall 2008 (August 25th December 6th 2008) 4 CHEM 6353: PHYSICAL ORGANIC CHEMISTRY Fall 2008 (August 25th December 2008) 6th 5 Question 3 20 points While Ognjen was in graduate school, an interesting paper appeared (J. Am. Chem. Soc. 2001, 123, 8428). The authors reported a study of the reaction of benzocyclobutanone with base. The pKa of benzocyclobutanone was estimated at ~25, which is significantly higher than the pKa of cyclobutanone (~20). Where does this difference come from? Would you expect the pKa of cyclobutenone to be higher or lower than that of benzocyclobutanone? Explain your reasoning. CHEM 6353: PHYSICAL ORGANIC CHEMISTRY Fall 2008 (August 25th December 6th 2008) 6 Question 4 30 points Provide a full orbital correlation diagram for the thermally allowed [6+4] cycloaddition of 1,3,5hexatriene and 1,3-butadiene. Be very careful about the relative energies and symmetries of orbitals in both cycloaddition partners. CHEM 6353: PHYSICAL ORGANIC CHEMISTRY Fall 2008 (August 25th December 6th 2008) 7 Question 5 40 points Bromination of the lactone shown below has often been referred to as the molecular somersault . Propose a reasonable mechanism for this transformation, and suggest two separate experiments that could prove your proposed mechanism. Be very specific in the description of these experiments; vague answers like "isotope labeling" will not count for much. CHEM 6353: PHYSICAL ORGANIC CHEMISTRY Fall 2008 (August 25th December 6th 2008) 8 If you need extra space, use this page. Clearly specify what problem you will be solving here. No external pieces of paper will be graded. CHEM 6353: PHYSICAL ORGANIC CHEMISTRY Fall 2008 (August 25th December 6th 2008)

Find millions of documents here - Study Guides, Homework Solutions, Papers, Exam Answer Keys and more. Course Hero has millions of course related materials that will enable you to learn better, faster and get an A in all your courses.
Below is a small sample set of documents: