Exam I NMR IR MS Diels-Alder Chem 241 Name___________________ Exam #1 February 28, 2001 CLOSED BOOK EXAM - No books or notes allowed. All work must be shown for full credit. You may use a calculator. Question Credit 1(20) 2(20) 3(15) 4(10) 5(15) 6(20) TOTAL 1) Please draw the product of a 6 + 2 reaction. Draw the MO diagram indicating the orbital symmetry, the HOMO and LUMO, and whether the reaction occurs thermally or photochemically. 2) The cyclopropenyl cation is a completely conjugated ring system. Please draw the cyclopropenyl cation and its MO diagram below 3a) Please draw the product of each of the following Diels-Alder reactions. O O + + C C Cl O O O + 3b) One of the two dienes below can be used in a Diels-Alder reaction and the other one cannot. Which one CANNOT be used and why? A. B. 4) Please draw the MO diagram for each of the following compounds. Circle the aromatic compounds (if any). H N 5) Please explain the endo rule and give an example Chem 241 Name___________________ Exam #1 February 28, 2001 CLOSED BOOK EXAM - No books or notes allowed. All work must be shown for full credit. You may use a calculator. Question Credit 1(20) 2(20) 3(15) 4(10) 5(15) 6(20) TOTAL 1) Please draw the product of a 6 + 2 reaction. Draw the MO diagram indicating the orbital symmetry, the HOMO and LUMO, and whether the reaction occurs thermally or photochemically. + - + - + - The HOMO of the 2 matches the LUMO of the 6 only if an electron is photochemically + - ++ - + HOMO moved. - + + - LUMO - + + - - + + - Thefore the reaction Zero of Energy occurs photochemically + - + - + + - - + + + + + + + - - - + + + + + + 2) The cyclopropenyl cation is a completely conjugated ring system. Please draw the cyclopropenyl cation and its MO diagram below - H H H 3a) Please draw the product of each of the following Diels-Alder reactions. O O O O + Cl + C C Cl O O O O O + O 3b) One of the two dienes below can be used in a Diels-Alder reaction and the other one cannot. Which one CANNOT be used and why? Rotate These groups hinder one another A. so the molecule does not want to take this shape. Rotate These groups do not hinder one another so the molecule can take B. this shape and do a Diels Alder. 4) Please draw the MO diagram for each of the following compounds. Circle the aromatic compounds (if any). H N 5) Please explain the endo rule and give an example Cl The endo rule says that the electron withdrawing group on the dienophile + C C Cl must overlap with the double bond from the diene (toward the interior of the molecule) Chem 241 Name___________________ Practice Exam #1 – NMR/IR/MS/MO Theory February 28, 2001 CLOSED BOOK EXAM - No books or notes allowed. All work must be shown for full credit. You may use a calculator. Question Credit 1(20) 2(20) 3(15) 4(10) 5(15) 6(20) TOTAL 1a) Using drawings, please show how a triplet is formed in NMR spectroscopy. 1b) What are the relative peak heights in a heptet? Show them as a ratio, ie. 1:2:1 etc. 1c) Please draw the complex NMR splitting diagram for the following molecule. J = AB 11, J = 9. Along with your diagram indicate where the signal would be found in the BC spectrum. H H H A B C Cl C C C H H H H 1d) Look at the complex splitting pattern shown below 10 2 8 2 2 6 2 2 8 2 10 What is the value of J and J ? AB BC J = J = AB BC J is a singlet, doublet, triplet, quartet (circle one) AB J is a singlet, doublet, triplet, quartet (circle one) BC 2a) Please explain why alkenes are found at 5-6 in an NMR but alkynes are found around 2.5. 2b) In NMR an alcohol and an acid OH differ in position by 8ppm. Please give two reasons why the acid OH is so much farther downfield. 3) Please draw the product of a 4 + 4 reaction. Draw the MO diagram indicating the orbital symmetry, the HOMO and LUMO, and if the reaction occurs thermally or photochemically. 4a) In Mass Spectrometry what are the approximate relative peak heights (in percent) for the following halogens, 35Cl = 37Cl = 79Br = 81Br = 4b) In IR the C-Cl bond is found at 754 cm-1 and the C-Br stretch is found at 548 cm-1. Which of these has the stronger force constant and by how much? C = 12g/mol, Cl = 35.45g/mol, Br = 79.9 g/mole 5) Please explain the endo rule and give an example. 6) Please draw the product of the following Diels-Alder reactions. O C O + C C C C CH 3 Cl + C C Chem 241 Name___________________ Practice Exam #1 – NMR/IR/MS/MO Theory February 28, 2001 CLOSED BOOK EXAM - No books or notes allowed. All work must be shown for full credit. You may use a calculator. Question Credit 1(20) 2(20) 3(15) 4(10) 5(15) 6(20) TOTAL 1a) Using drawings, please show how a triplet is formed in NMR spectroscopy. 1:2:1 1b) What are the relative peak heights in a heptet? Show them as a ratio, ie. 1:2:1 etc. Singlet 1 Doublet 1 1 Triplet 1 2 1 Quartet 1 3 3 1 Pentet 1 4 6 4 1 Hextet 1 5 10 10 5 1 Heptet 1 6 15 20 15 6 1 1c) Please draw the complex NMR splitting diagram for the following molecule. J = AB 11, J = 9. Along with your diagram indicate where the signal would be found in the BC spectrum. ~ 2.0 H H H A B C Cl C C C H 11 11 H H H 9 4 5 4 4 1 4 4 5 4 9 1d) Look at the complex splitting pattern shown below 10 2 8 2 2 6 2 2 8 2 10 What is the value of J and J ? AB BC J = 12 J = 10 AB BC J is a singlet, doublet, triplet, quartet (circle one) AB J is a singlet, doublet, triplet, quartet (circle one) BC 2a) Please explain why alkenes are found at 5-6 in an NMR but alkynes are found around 2.5. H H C C H C C H H H Since the ring current in an alkene pulls electrons away from the hydrogens they are pulled downfield as compared to an alkyne whose circulating electrons help shield its hydrogens. 2b) In NMR an alcohol and an acid OH differ in position by 8ppm. Please give two reasons why the acid OH is so much farther downfield. a) The extra oxygen on an acid pulls more electron density out of the OH bond forcing it further downfield. b) An acid group has a C=O which sets up ring currents that pull electrons out of the atoms to which they are attached and this pulls the OH group farther downfield.