First Three Letters of Last Name: TA Name: Hour Exam #1 K E Y 5.12 Spring 2005 Organic Chemistry 1 I Printed name Signature ID# Pre-requisite (circle one): 5.112 5.111 3.091 1. Make sure your exam has 9 numbered pages plus a periodic table. 2. Write your initials on each page. 3. Look over the entire exam before you begin to familiarize yourself with its length. Do what you know first, then attempt the harder problems. 4. Read the instructions carefully and budget your time. 5. Show all of your work. Partial credit receives points! Page 1 2 3 Possible Points 6 Total 16 10 4 5 6 7 8 10 16 12 12 18 Total 9 100 XC 4 104 1. (1 pt) What is the pka of a sp hybrdized carbon atom? (a) 25 b) 35 c) 45 d) 50 2. (2 pts) a) Circle the letter of the molecule with the lowest barrier to rotation (or ring- flip). b) Box the letter of the molelcule with the highest barrier to rotation (or ring-flip). (a) ethane b) propane c) butane cyclohexane 3. (2 pts) Rank the following substituents in order of priority (1 = highest priority). 4-CH=CH2 2 -CN 3 -CH2NH2 -CH2Br 4. (1 pt) If a chiral molecule has an absolute configuration of R, which direction does it rotate the plane of polarized light? a) clockwise (dextroratory) b) counterclockwise (levarotatory) c) it doesn't rotate the plane of polarized light can't be determined from the information given 5. (6 pts) a) Enter the pk, value for each acid in the boxes below. b) Indicate whether the reactants or products will be favored at equilibrium by circling the appropriate set of equilibrium arrows (a longer arrow is drawn toward the species favored at equilibrium). OH Θ + H-O or + H H 8-11 15.7 H3C +H3C-N-H 1 H or H3C OH + H3C-N-H HC-N-H 16-11 H 1+ 4-5 6. (10 pts) a) Provide structures in the boxes to complete the following acid-base (proton- transfer) reactions. b) For each set of reactants, draw in all lone pairs of electrons and show the electron movement by using curved arrows. c) Indicate whether the reactants or products will be favored at equilibrium by circling the appropriate set of equilibrium arrows. 10. (16 pts) a) Draw the 4 major resonance contributors for the molecule shown in the first box. Partially completed structures are provided as a time-saver. Do not generate any additional charges. b) Draw in all lone pairs of electrons and use arrows to show the movement of electrons within the structure. c) Place a checkmark in the small boxes of the three structures that contribute the most to the resonance hybrid. d) Circle all the nucleophilic atoms in the structure at the bottom of the page.