CH251Midterm1AU2009BLANK

CH251Midterm1AU2009BLANK - Callam Chemistry 251 Autumn...

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Unformatted text preview: Callam Chemistry 251 Autumn 2009 Midterm 1 200 points IH 100 – Tuesday, October 16, 2009 Name (PRINT)_____________________________________________________________ I have neither given or received aid on this exam(SIGN)___________________________________________________________ Place an X in the column next to your recitation section. Failure to mark your correct recitation section will result in –5 points from your exam total. Day Time Room Teaching Assistant Tuesday Tuesday Thursday Thursday Tuesday Tuesday Thursday Thursday Tuesday Tuesday Thursday Thursday 1:30 pm – 2:18 pm 1:30 pm – 2:18 pm 1:30 pm – 2:18 pm 1:30 pm – 2:18 pm 2:30 pm – 3:18 pm 2:30 pm – 3:18 pm 2:30 pm – 3:18 pm 2:30 pm – 3:18 pm 3:30 pm – 4:18 pm 3:30 pm – 4:18 pm 3:30 pm – 4:18 pm 3:30 pm – 4:18 pm AV214 MP1008 SM2186 MP1008 SM2186 MP1008 SM2186 MP1008 KL330 AV214 KL330 AV214 Christopher McDaniel Chad Eichman Christopher McDaniel Chad Eichman Christopher McDaniel Chad Eichman Christopher McDaniel Chad Eichman Chad Eichman Christopher McDaniel Chad Eichman Christopher McDaniel Section 1 2 3 4 5 6 7 Extra Credit Total Points 25 15 30 50 20 25 35 10 200 Score Please read all of the directions for each section of the exam carefully. There are 10 pages including this cover page for Midterm #1, please check to make sure you have all of the pages. Make sure your answers are clear. Any structures or answers that are unclear or ambiguous are considered wrong. 1/10 Points/Page = Callam Chemistry 251 Autumn 2009 Part 1. Functional Groups. For each of the molecules below write the name of the major functional group present on the line below each structure. (1 point each for a total of 25 points) O N O OH O N O N O N O O O OH S O OH N OH O O OO S Cl N O N O O N H N H O H O N O O O O SH O OM g N C O 2/10 Points/Page = Callam Chemistry 251 Autumn 2009 Part 2. Nomenclature. (3 points each for a total of 15 points) (a) For each of the following structures provide the IUPAC name. (CH3)2C(CH2CH3)2 (b) For each of the following IUPAC names draw the skeletal structure in the space provided below. 1 ­cyclobutyl 2 ­methylcyclohexane 2 ­ethyl ­1,1,3,3 ­tetramethylcyclopentane 3/10 Points/Page = Callam Chemistry 251 Autumn 2009 Part 3. Resonance. For each of the following structures draw the indicated number of resonance forms and label the best resonance form. (15 points each for a total of 30 points) (a) 5 additional resonance structures O OH N (b) 4 additional resonance structures HO N 4/10 Points/Page = Callam Chemistry 251 Autumn 2009 Part 4. Acids and Bases. (50 points) (a) For each of the following reactions (10 points each for at total of 40 points): Draw the products of the reaction (4 points); Use curved arrows to represent the electron movement between the acid and base. (2 points); Predict which direction the equilibrium lies towards. (2 points); Justify your answer with one of the four factors that determine acidity (using a minimum of words). (2 points) F3C (i) OH + ONa HO (ii) N H + H H O H O (iii) LiO N H Li + H H O H Cl (iv) Cl N H H N H H + Na O H (b) Write a stepwise reaction sequence using your knowledge of acid base chemistry to show how the following reaction occurs. Your answer should include curved arrows to show which bonds are breaking and which bonds are formed. Two separate steps involving acid/base reactions will be necessary to arrive at the product. (10 points) N H 3C N + NaOH + H2O + NaOH + H2O N H 3C N H H Step 1: Step 2: 5/10 Points/Page = Callam Chemistry 251 Autumn 2009 Part 5. Hybridization. (20 points) (a) Answer the following questions based on the structure shown below. (2 points each for a total of 10 points) O O N HN O A (i) What is the molecular formula of the above molecule? (ii) How many carbons are sp3 hybridized? (iii) How many lone pairs are implied? (iv) What orbitals are overlapping to make the bond labeled A? (v) Label the three most acidic hydrogens in the molecule. (b) Draw a clear molecular orbital pictures for both of the resonance forms shown below. You should draw all of the p orbitals in pen and all of the hybridized orbitals in pencil. Make sure that your drawing is clear. Your drawing should take into account bond angle and dimensions of the orbitals (use descriptions such as parallel or perpendicular to the paper if needed). (10 points) O H O H 6/10 Points/Page = Callam Chemistry 251 Autumn 2009 Part 6. Newman Projections. (a) Using Newman projections, draw all of the staggered and eclipsed conformers of 2,3 ­dimethylpentane with respect to rotation about the C2 ­C3 bond. Assign the relative energies of the conformers. (20 points) 1 2 3 4 5 60° 60° S1 Energy = Energy = Energy = 60° 60° 60° Energy = Energy = Energy Values: CH3, CH2CH3 (gauche) = 1.0 kcal/mol CH3, CH3 (gauche) = 0.9 kcal/mol H, H (eclipse) = 1.0 kcal/mol H, CH3 (eclipse) = 1.4 kcal/mol H, CH2CH3 (eclipse) = 1.5 kcal/mol CH3, CH3 (eclipse) = 4.0 kcal/mol CH3, CH2CH3 (eclipse) = 4.5 kcal/mol CH2CH3, CH2CH3 (eclipse) = 5.7 kcal/mol Energy = (b) What is the barrier to rotation around the C2 ­C3 bond of 2,3 dimethylpentane? (5 points) 7/10 Points/Page = Callam Chemistry 251 Autumn 2009 Part 7. Cycloalkanes. (a) In lecture we learned cyclopentanes can adopt low energy envelope conformations. In methylcyclopentane, the envelope that places the CH3 group at the “flap” of the envelope (A) is lower in energy than the conformation that places the CH3 group at the “base” of the envelope (B). Draw Newman projections along the C1 ­C2 indicated bonds in A and B. Use these Newman projection to help you explain the energy difference between A and B. (10 points) HH H H H 2 H HH A 1 CH3 H H 1 H 2H H H H H H H3C H (b) At 298 K, the equilibrium percentages are 73% (A) and 27% (B). Using the equation below calculate the ∆G° between the two conformations. (5 points) B ∆G° =  ­2.303 RT log Keq R = 0.001987 kcal/(K mol) T = Temperature Kelvin (K) 8/10 Points/Page = Callam Chemistry 251 Autumn 2009 (c) For each of the following, draw both possible chair conformations and circle the one that is preferred. Calculate the relative energy difference between the two conformations using the following information. A values : (CH3 = 1.7 kcal/mol), (COCH3 = 1.35 kcal/mol) (20 points) (i) CH3 CH3 H3C (ii) CH3 O 9/10 Points/Page = Callam Chemistry 251 Autumn 2009 Extra Credit. (10 points) The following overall reaction takes place via two aequenial acid/base reactions. The first is a Bronsted ­Lowry acid base reaction and the second is a Lewis Acid base reaction. Write each of the individual reactions with arrows representing electron movement and the appropriate labels (acid/base/electrophile/nucleophile) that show how the products are produced. Na N H + H HBH H H2 + Na Cl + N BH3 Cl Reaction 1: Reaction 2: 1 2 3 I H Li Na II Be Mg Partial Periodic Table III IV B C Al Si V N P VI O S VII F Cl VIII He Ne Ar 10/10 Points/Page = ...
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